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Stand alone FOC fork?

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lizardmech
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Stand alone FOC fork?

Have you ever considered making a lightweight portable version of the FOC code to speed up development and aid in adapting it to different projects? The VESC works great for a user friendly adaptable motor controller but the enormous scope of the firmware and features make heavy customization extremely difficult. Porting the entire firmware to any other MCU is also extreme in its current form, chibiOS rarely gets ported to much and even with full chibiOS ports the VESC firmware itself contains considerable STM32F4 specific code.

At the moment anyone researching motor control or trying to build an open FOC controller has very little to choose from. Reference software from hardware manufacturers is either closed source or if open purposely not updated to try and push people into using proprietary control software. Feature and performance wise the VESC FOC software is great but out of necessity to work with the existing code much of the FOC specific code is intertwined with BLDC parts and other sections not specific to motor control.

Interested to know if Benjamin thinks its worth while and feasible even if he doesn't work on it directly and if any other people would be interested in such a thing. 

arvidb
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I intend to try to do exactly this. The current firmware is an amazing achievement, but from a maintenance point of view, it's a nightmare. Everything is intertwined, volatile is used indesciminately instead of thought-through use of synchronization primitives (this is particularly nasty), etc.

What's needed is a separation of functionality: a framework for different sensor types (with self-contained code for each specific sensor), a generic implementation of controllers (PID and/or others), separate access functions for the PWM and sample timers... I've done some preliminary attempts at this, mostly to familiarise myself with the code, and I'm leaning towards your suggested method of re-implementing a subset of the functionality to get going. It's incredibly hard work to figure out what some of the code does. Try to figure out correct_hall() in mcpwm_foc.c for example... The problem there is that it mixes specialized initialization behaviour and decisions on what sensor to use (hall or observer?) with hall interpolation. It's almost impossible to maintain in the long run - my hat's off to Benjamin for managing it so far!

At the moment I'm trying to put together a dynamometer so that I can script a test suite and do regression testing. I think that's a requisite for any serious work on the firmware.

It's slow going though since I have ME/CFS and thus very little energy for this.

arvidb
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BTW, when you say "lightweight", what does that mean to you, functionality-wise? Which features should be included, what doesn't need to be included?

lizardmech
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I was thinking perhaps a series of portable modules that are hardware agnostic. Something similar to what you see with model based development on things like matlab, there's a bunch of other ones for MCUs and FPGA. They all pretty much do the same thing, they have the core FOC modules written in C and users just connect the MCU peripherals via a gui, but the same approach can be done manually if you have properly designed modules.

In terms of modules my rough idea would be:

Highest priority-

Sensorless observer code, needs to be abstracted so it just has data input and output no MCU settings, documenting this section should be a priority, information on how to build an observer as advanced as the one in the VESC is extremely rare. I think pwm_foc.c requires digitalfilter.c. Digitalfilter.c is very nice and pretty much the perfect example of how to split things into macros or modules.

Motor and  hall parameter detection, also critical to document. At the moment it's intertwined with the observer and other FOC code.

Moderate priority -

SVM code, common and well documented code probably should still be abstracted as other examples seem to vary somewhat and using others could cause complications with the observer.

PID loops for current, speed etc. very useful to have but fairly common code with plenty of examples and tutorials around.

Low priority-

Some sort of module to enable very basic functions with VESC tool, firmware flashing and advanced features won't work but it would be good to still be able to use basic controls, data and various charts.

I found this code for a Ti MCU a while ago. it's inferior to the VESC but the way in which the motor control components are broken down is very nice and might be a good example of how everything could be turned into modules that are abstracted from MCU specific code. smopos.h is the sensorless observer and probably the best example to look at. 

https://github.com/lizardmech/ti_delfino/tree/master/include/motorcontrol

arvidb
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Unless I'm missing something, the observer code (observer_update() in mcpwm_foc.c) is actually very well documented through the PDF linked in the code, and also has no MCU dependencies. It does use global variables and it passes internal state variables as parameters, which are both not good practise. It should be one of the easier parts to modularize though (which would also take care of the global vars and state variable problems).

SVM and PID control are both used by the FOC code (and also in practice by the trapezoidal/BLDC code by the way, at least if you want motor current limiting), so in case you want motor control at all, SVM and PID modules need to be implemented/extracted first. Along with a FOC module? The algorithms for sensorless startup, motor parameter detection, and hall sensor detection should be extracted to their own modules.

I'm thinking things that could be left out would be the different control modes: duty cycle, speed, pos, braking. These are all intertwined with the pwm code today, and really shouldn't be. (Well, duty cycle in BLDC mode has to be of course.)

lizardmech
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Sounds reasonable, the observer theory is reasonably well documented but it's been thoroughly enhanced by Benjamin over the years as well. It looks like there's various signal conditioning  being done it's a bit of a mystery as to why and how it works. I didn't see such filtering on other controllers I looked at. One interesting thing I noticed, virtually all the commercial solutions I looked at used IQ math instead of floats, didn't appear to have digital filtering and are convoluted in their attempts to scale the IQ math, I suspect this is why I have found the VESC much more robust when it comes to motor detection and running on different inverters.

arvidb
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I wrote before that indiscriminate use of volatile instead of proper synchronization primitives is nasty. I'm trying to figure out what "proper synchronization primitives" means in ChibiOS/STM32F4 (which is an ARM Cortex-M4 processor and uses the Armv7-M instruction set, BTW).

For my own sake I feel I need to sum up here why volatile is bad and what is needed instead. Maybe others will find it interesting, too. :)

In C, 'volatile' is a type qualifier which forces the compiler to output instructions to actually read or write memory every time the variable is accessed (instead of e.g. placing the value in a register). It also makes the compiler respect order between volatile accesses. But volatile accesses are not atomic (i.e. they can be interrupted/preempted), nor do they ensure that the hardware executes memory accesses in order. They also (obviously) doesn't make related assignments to different variables atomic (e.g. updates to i_alpha and i_beta in the VESC firmware).

Since most things happen in the ADC interrupt service routine in the VESC firmware anyway, most of the problems associated with using volatile for synchronization (but also most of the cause for using it) should be void. But I want to "untangle" the firmware so that, for example, only the things that really have to be done in the ISR is done there. I want to enable sensor input using interrupts, running position and speed loops at lower frequency than the PWM frequency, etc. This will require proper synchronization.

As I understand it, proper synchronization on an ARM v7 CPU requires three things:

  • A compiler barrier that prevents the compiler from reordering instructions over the barrier, and makes it flush data held in registers.
  • A memory barrier that prevents the hardware from rearranging memory accesses over the barrier. (Also instruction barrier?)
  • Code to prevent preemption while the critical section is executed.

But ChibiOS doesn't seem to have this proper implementation. There are mutexes, which are not usable from ISRs. There are also semaphores, but they are primarily meant for signalling between producers and consumers. Strangely it seems they don't make use of barriers (i.e. they only implement the last point above). There is the chSysLock() function, but looking at the implementation it just disables interrupts on ARMCMx (while on AVR it actually inserts a compiler barrier, as it should). It seems ChibiOS is severely lacking here?

The Linux kernel implements a barrier for STM32. It looks like this (from arch/arm/include/asm/barrier.h):

asm volatile ("DSB" : : : "memory");

This is a combination of a compiler barrier and the DSB ("Data Synchronization Barrier") instruction.

Here's a little background about the DSB instruction on ARM v7: http://infocenter.arm.com/help/topic/com.arm.doc.faqs/ka14041.html

Any ideas? I'm leaning towards writing my own code for critical sections. But it can be tricky getting it right!

TheFallen
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I personal would love to see the back of ChibiOS. I get the advantages that it brings, but I don't feel that they're really all that helpful for an ESC.

benjamin
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A simple FOC implementation can of course be made, and there is a lot of information out there on how to do that. I could probably make a motor spin using FOC on any STM32 in a day or two with 5% of the VESC code. The difficult part in order to make it work for the first time without experience is to get all the details right. A wrong sign, a bad scaling, a missing SQRT(3) or many other tiny mistake will just prevent it from working at all, which is a big threshold in the beginning. Then when the motor can spin and works well enough for a simple pump application, all other applications make things more and more difficult to be handled by the same implementation.

The difficulty in the VESC code is really to get all the details right under all operating conditions with all motors in all applications. For example, when the motor is already moving when starting but undriven, the observer has to use different sources of information to track the motor, and the PWM modulation has to be set up exactly right to make a smooth transition. The temperature backoffs and detection functions for motor parameters and encoders are also tricky. There is not any special algorithm in the VESC that makes it work well, it is hundreds of small details.

I agree that the code can be cleaned up, the main problem is that I don't have much time and too much work to do. A proper test bench where testing of all corner cases can be done would also help a lot, which is something that I currently don't have set up.

Regarding the use of volatile, it is not about being atomic, it is about not optimizing certain things away where threads and interrupts share variables and need to be synchronized, which is something that chibios does not support too well. For example, things like this

for (float i = 0.0;i < 2.0 * M_PI;i += (2.0 * M_PI) / 500.0) {
		m_phase_now_override = i;
		chThdSleepMilliseconds(1);
}

would sometimes not work properly as the optimization would omit writing i to m_phase_now_override every iteration and instead do it at the end. In general I have made state variables that are shared between interrupts and the rest of the file volatile to avoid this. By analyzing everything most of the voltatiles can probably be removed, or completely different ways to synchronize things can be used, but I haven't given it that much priority.

Some functions have functionality that can be moved outside, such as the interpolation in correct_hall, but that interpolation is so far only used there and I did not find it worth the effort to move it out and make it general before using it in a similar way in other places. Functions and macros that are used in several places are in the utils files. I also made an effort to put common motor control functionality that can be abstracted into mc_interface, such as the backoff functions, ah counters, rt data filtering etc.

The PID controllers are used in several places, but the implementation are quite specific with many corner cases. The most simple PID controller can be implemented in a few lines of code, such as this

previous_error = 0
integral = 0
loop:
  error = setpoint - measured_value
  integral = integral + error * dt
  derivative = (error - previous_error) / dt
  output = Kp * error + Ki * integral + Kd * derivative
  previous_error = error
  wait(dt)
  goto loop

This could be put in a function, where the inputs are the setpoint, the current value, the control parameters and the time since the last execution. Then the function would keep track of the state, or the state could be allocated beforehand and passed to the function on every execution which is cleaner because it avoids side effects. In some cases it is not enough to just pass the state, the state also has to be altered based on conditions in the system. For example, the duty-based speed controller in the BLDC implementation has to set the integrator to the duty cycle with some scaling when it is activated at speed to get a smooth start, and not a jump. The state of the PI controllers and the order of operations in the control_current function also is very sensitive to initial conditions when starting the controller while the motor already is at speed. Taking all of this into account, the generalized controller can become quite complicated to work with, with all special cases, and every time the most demanding case is updated (such as control_current which I have updated a lot of times to make things smooth) it will affect the usage everywhere else. Therefore my preference has been to make every PID controller in place, as the most basic implementation is simpler to understand and see than the generalization for all cases used in the code.

Going back to the correct_hall function, it does not only take care of interpolation, it also handles transitioning between sensored and sensorless operation, moving to sensorless when hall sensors give invalid values, hysteresis between transitions, behaving correctly when the motor is run in open loop and other things. Making all of this general would make that function explode into different files and me putting effort into making nice interfaces for many things that are only used once in a specific way.

The problem there is that it mixes specialized initialization behaviour and decisions on what sensor to use (hall or observer?) with hall interpolation. It's almost impossible to maintain in the long run - my hat's off to Benjamin for managing it so far!

Reading things like this is not very encouraging. I have put in a lot of effort into making the best implementation decisions given the time I have available, and tried to generalize everything that makes sense generalizing. Many things have very specific details, and making them general while making room for the details would make things explode. As far as I know there is nothing major in the code that would pay off generalizing any time soon in future work with even close to the amount of work that goes into making it general.

lizardmech
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The difficulty in the VESC code is really to get all the details right under all operating conditions with all motors in all applications. For example, when the motor is already moving when starting but undriven, the observer has to use different sources of information to track the motor, and the PWM modulation has to be set up exactly right to make a smooth transition. The temperature backoffs and detection functions for motor parameters and encoders are also tricky. There is not any special algorithm in the VESC that makes it work well, it is hundreds of small details.

I agree that the code can be cleaned up, the main problem is that I don't have much time and too much work to do. A proper test bench where testing of all corner cases can be done would also help a lot, which is something that I currently don't have set up.

That's a good point about keeping things such as hall and observer together. I think users here can probably manage to do it without taking up your time if pointed in the right direction the hard part is getting the initial plan and realistic goals.

The main question as to feasibility and if it's worth while would be:

- How critical is chibiOS when it comes to the FOC motor control portions? Is taking the FOC code and setting it up to run without a RTOS a realistic goal?

- Relocating MCU specific code outside of mcpwm_foc.c and other motor control sections, seems like perhaps the most time consuming and challenging aspect but it would make using different MCUs and motor control specific code could be shared between anything that ventures far from mainline VESC builds. Possible or unrealistic?

- I rough idea of which files the foc code is spread over, or a just a very basic diagram how information is routed. I think I have a basic idea of how it works, PWM timer triggers ADC, ADC outputs scaled based on the hardware config, I'm a little lost after here, some go straight to the observer others are filtered by the code in digitalfilter.h? The rest is fairly easy to read, observer calculates error and feeds SVM module the required data to correct which then in turn sets the correct duty cycle. 

arvidb
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Hi Benjamin, and thanks for the answer! I wrote above that I think the VESC firmware is an amazing achievement, and I mean that! It's probably at the limit of what can reasonably be expected from one very dedicated person! So please don't feel discouraged. But since you open sourced it, we have the possibility to make it even better!

I realise its functionality is very complex - but that is a reason for data encapsulation and modularization, not against it! (Data encapsulation allows generalization, but encapsulation is useful even if generalization is not desirable, since it improves code clarity.)

Note that I'm also not saying that I think restructuring of the code should be your top priority. (Hey, that 18 FET, 75 V, 300 A VESC seems like a worthwhile project! yes). I'm saying this is something I'd like to work at. I'm also not trying to compete with you - the best possible outcome would be if I (or someone else) did the work, you took a look at it and said "Wow, this will make further development so much easier!" and ended up releasing it as a new major version of the VESC firmware.

Let's face it: it's really difficult to make changes to the current code, and understand how that will affect the whole. Say I wanted to add support for a new sensor, or make a change to how sensor data is combined. Since everything is in the same file, and makes plenty use of global variables, it's hard to know where to even begin - and even harder to ensure the changes doesn't have unintended side effects.

And I  think that's where lizardmech's request for a "version of the FOC code to speed up development and aid in adapting it to different projects" comes in. In the end it doesn't even have to have less features than the current firmware. Heck, look at the Linux kernel. That is an incredibly complex behemoth, but since it's well structured, it's relatively easy to work on! Even by lots of people simultaneously!

A quick example of what kind of restructuring I'm talking about. Take mcpwm_foc_hall_detect(). It uses a set of global variables (m_phase_override, m_phase_now_override, m_id_set, m_iq_set, m_control_mode, and m_state) to tell other code to listen to it instead of listening to the "normal" setpoints. This other code has to handle the special case of the override. mcpwm_foc_hall_detect() writes the detected data to hall_table[] which is returned to commands_process_packet() in commands.c which in turn writes it to a configuration(?) and returns it to VESC Tool(?).

What if instead it worked like this: hall_detect(hall, controller) in hall.c was called. "hall" is of type "struct hall" and (as you say above) contains the internal state of the hall sensor (i.e. its hall_table). "controller" is a "struct controller" containing, among other things, a method set_phase(angle, current) that tells the controller (be it SVM or BLDC) to set the stator currents to that angle and current. So hall_detect() could iterate over controller->set_phase(angle, current), recording the hall values as it went along into its internal state struct. Two things are won here: hall internal state is kept in one place, and the controller code doesn't have to bother with the special case of sensor detection. (commands_process_packet() could of course call hall_get_raw_table(hall, &table) or similar to make it possible to see the results of the detection in VESC Tool, but the ownership of the data would be clear.)

In the same way, speed and position controllers could be "extracted" to use a general interface to set the motor current. The code would be a lot simpler to understand and maintain, and would work at least as well.

This is my vision at least; one that makes me excited about working on this. smiley

arvidb
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That's a good point about keeping things such as hall and observer together. I think users here can probably manage to do it without taking up your time if pointed in the right direction the hard part is getting the initial plan and realistic goals.

No, that's actually a very good reason to encapsulate them as much as possible, so that the needed interactions becomes explicit and obvious! Just saying... ;)

benjamin
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Thanks for the feedback, it is actually nice that others than me are looking at the code and suggesting improvements.

- How critical is chibiOS when it comes to the FOC motor control portions? Is taking the FOC code and setting it up to run without a RTOS a realistic goal?

The code did actually not use chibios a long time ago, but there are many advantages to using it and chibios is actually really nice and convenient to work with. Writing custom applications becomes much easier, and handling all the applications, communication interfaces, hw drivers with DMA, interrupts etc. becomes easier. For example, this would not be possible in the same way without chibios:

http://vedder.se/2015/08/vesc-writing-custom-applications/

Say I wanted to add support for a new sensor, or make a change to how sensor data is combined. Since everything is in the same file, and makes plenty use of global variables, it's hard to know where to even begin - and even harder to ensure the changes doesn't have unintended side effects.

Adding a new type of encoder can be done without changing mcpwm_foc.c at all. encoder.c is responsible for giving an encoder reading in the range 0 - 360 degrees when asked for it, and it has some functionality to deal with index pulses and wether or not they are found. The tricky and specific parts with encoders is that one encoder revolution most of the time is not mapped to one electrical motor revolution, and the position controller works in terms of encoder revolutions to not throw away information. This requires some scaling and mapping that is quite specific to how the motor control works internally, which is why I put it there. This way new encoders can be implemented without dealing with those specifics, as long as their position can be read as a float in the range of 0 - 360 degrees. I don't think it is worth moving out the encoder detection of mcpwm.c now, as it is so deeply connected.

Hall sensors could maybe be seen as an encoder with the lowest possible resolution to work at all, but by handling them as a special case gives better performance, which I found important as they are quite common and an extreme case of an encoder. I don't think it would make sense to add some sensor with just slightly higher resolution than hall sensors, which is why all other sensors in the future most likely fit nicely into the encoder implementation.

A quick example of what kind of restructuring I'm talking about. Take mcpwm_foc_hall_detect(). It uses a set of global variables (m_phase_override, m_phase_now_override, m_id_set, m_iq_set, m_control_mode, and m_state) to tell other code to listen to it instead of listening to the "normal" setpoints. This other code has to handle the special case of the override. mcpwm_foc_hall_detect() writes the detected data to hall_table[] which is returned to commands_process_packet() in commands.c which in turn writes it to a configuration(?) and returns it to VESC Tool(?).

What if instead it worked like this: hall_detect(hall, controller) in hall.c was called. "hall" is of type "struct hall" and (as you say above) contains the internal state of the hall sensor (i.e. its hall_table). "controller" is a "struct controller" containing, among other things, a method set_phase(angle, current) that tells the controller (be it SVM or BLDC) to set the stator currents to that angle and current. So hall_detect() could iterate over controller->set_phase(angle, current), recording the hall values as it went along into its internal state struct. Two things are won here: hall internal state is kept in one place, and the controller code doesn't have to bother with the special case of sensor detection. (commands_process_packet() could of course call hall_get_raw_table(hall, &table) or similar to make it possible to see the results of the detection in VESC Tool, but the ownership of the data would be clear.)

The hall table is owned by mc_interface.c (as all other settings in the motor configuration) and conf_general.c handles storing and reading them from flash (to retain them through power cycles) as well as providing default values for everything, which also can be overridden as a specific file generated from VESC Tool if desired. mcpwm_foc and mcpwm are not allowed to change the configuration (although they do it temporally in a few places and change it back while locking the interface, could be done nicer). The hall_detect function returns a hall table that is passed to VESC Tool. Vesc Tool is then responsible for putting it into the configuration and writing it back, as with all the other detected settings.

The state variables (which are not global, they are only visible in that file) that are changed to do sensor detection are not part of any control mode, and quite specific to that task. Making them part of the interface allowing to make sensor detection from the outside would as it looks now only be useful for that specific task, which is why I haven't put effort into doing that yet.

The hall detect function is a lot simpler than the encoder detection, but I still think it makes sense to keep it in mcpwm.c. That is because the hall table is specific to the foc implementation, and bldc has a different type of hall table in the configuration. (and yes, the BLDC implementation is a mess that needs to be cleaned up, but my focus has been on FOC for a while).

lizardmech
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The code did actually not use chibios a long time ago, but there are many advantages to using it and chibios is actually really nice and convenient to work with. Writing custom applications becomes much easier, and handling all the applications, communication interfaces, hw drivers with DMA, interrupts etc. becomes easier. For example, this would not be possible in the same way without chibios:

http://vedder.se/2015/08/vesc-writing-custom-applications/

I think the VESC works great for it's intended purpose with chibiOS as it is now. Where it becomes a headache is if you deviate much from its original purpose. For example I have been trying to get someone to write a custom VESC app to use an IMU to control balancing vehicles and robots for maybe 2.5 years, so far I have gone through maybe 4 or 5 different freelance embedded devs and a few thousand dollars. The problem is I couldn't find anyone familiar with chibiOS and information is scarce due to it's relative obscurity. With one of them his day job was even writing low level assembly code for a MCU manufacturer, if I had just been able to give him code running directly on the MCU he would have been able to sort out all the low level stuff and get it done in a few days, instead he got stuck because he couldn't find out how to to integrate the driver into chibiOS and then access it in a VESC app.

The other issue with chibiOS is it confines it to the STM32F4, which again isn't an issue for the VESC in it's usual configuration. But for example if you take a project like that guy building a high power VESC  for an EV the STM32F4 starts to become a limitation, it doesn't have Sigma delta filters on the MCU for easy access to isolated sensors. I think he was looking into adding an entire FPGA just to try and get the signals to the MCU. There's other options such as modulators that convert the signal back to differential analogue on the isolated side which can then be converted to single ended 3.3v signals with op amps but going through multiple analogue to digital conversion + opamps lowers performance and increases needed components dramatically.

Another example is higher switching freq, with the newest GaN transistors it can be desirable to have 100khz+ PWM to produce compact inverters that only need ceramic capacitors, it also potentially opens up controlling motors that feature extreme ERPM requirements or high efficiency coreless motors that have very low inductance. But again when confined to the STM32F4 it's not really possible. These days you can get very high powered M7 cores with high res PWM or others with dedicated trigonometry hardware that do FOC loops in around 1 us. 

I'm not sure what the best solution is, asking for specific features to be added to the mainline VESC for a certain project seems unreasonable in many cases and then certain features would break required features to keep it nice and easy for the people running official hardware. Which got me thinking about the possibility of a minimalistic fork or branch people can port or build on top of. While manually doing all the low level MCU interrupt, DMA and PWM settings is time consuming it's something people can do themselves by studying MCU datasheets and readily available information. In contrast trying to build on top of the mainline VESC and using chibiOS is easy for you because you're familiar with the code while when anyone else tries it it quickly turns into them having to ask how and why you did something with the chibiOS abstraction. Because of that it ends up wasting your time with questions on the forum or others are unable to get anywhere because you don't have time to explain how various things are abstracted via the RTOS.

The way I see it at the moment the primary limitation on VESC development is how much time you have to work on it. On the mainline VESC having chibiOS and abstraction enables you to spend less time on mundane programing aspects, removing it would decrease productivity. But it's the opposite when it comes to anyone trying to customize it as they take up time with questions on the forum and your youtube account. This means changing the VESC heavily to suit the second group would be counter productive. To me the most efficient option seems to have a second branch aimed at people building heavily customized projects is the easiest way, odds are they have no interest in non-FOC sections or something like maintaining compatibility with 4.10 VESCs. You could also use it to test new features potentially dangerous to hardware, it would help protect against random trampa VESC 6 users mistakenly uploading beta or customized firmware and killing hardware. I'm not certain if it's a good idea, just trying to come up with ideas in general to see what people think or if anyone else has some better ideas. 

arvidb
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lizardmech: I don't see how removing ChibiOS and writing the corresponding code manually would make porting to another MCU easier? You would have to rewrite that code anyway for the new MCU... Also note that most of the hardware setup seems to be done through the STM32F4 Standard Peripherals Library, which is not really part of ChibiOS. But again, even if you wrote all that code by hand to get rid of the dependency, you'd have to rewrite it all for a new MCU family anyway.

Also, I have the feeling that you (or rather your programmers) blame ChibiOS for things that aren't ChibiOS's fault. It's not that difficult to understand ChibiOS - all the code is there, and it's a pretty thin layer. It's probably that they are unfamiliar with the VESC firmware in general that's the problem. Which IMU unit are you using?

arvidb
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Benjamin:

I don't think it is worth moving out the encoder detection of mcpwm.c now, as it is so deeply connected.

It's exactly because it's so deeply connected that it would be worthwile extracting it. It would be a PITA to do, but it would make the code much clearer and easier to maintain.

But I digress; I can see you're not convinced. :)

The state variables that are changed to do sensor detection are not part of any control mode

I know it isn't implemented as an externally accessible control mode, but isn't this pretty much the "handbrake" mode? I.e. run the motor openloop with a specified current (and phase). Or put othwerwise: both handbrake and sensor detection could be run through the same set_phase() method.

The hall table is owned by mc_interface.c (as all other settings in the motor configuration) and conf_general.c handles storing and reading them from flash

Yes, I can see now the rationale behind keeping all the configuration data in one place. Thanks for making that clear to me. It is unfortunate however, since it lands us in the exact opposite corner of the data encapsulation paradigm (object orientation) which is considered good practice (and for good reasons!). It would probably have been better to encapsulate data and have each object supply its own defaults as well as serialise it for flash storage. But it's always easy to be wise after the event...

The state variables (which are not global, they are only visible in that file)

In my experience, C variables that are declared to be visible within an entire compilation unit (.c file) and have the same lifetime as the program, are considered global (i.e. they don't have to have external linkage). But regardless of terminology, IMO the fact that these variables are "globally accessible within that file" is an important part of what makes it so hard to see what's going on.

lizardmech
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I was trying to use the same family of IMU Benjamin uses here https://github.com/vedderb/rise_sdvp/blob/master/Embedded/RC_Controller/... Where I got stuck was where to place the IMU code in the VESC build and which files outside of the app would need to be updated to access the IMU in a control app. If I could have gotten past that stage I probably could have finished it, I know I had to run a kalman filter on the raw data, configure PID loops and use it to command motor current, I wasn't 100% sure what to do with the threads and memory settings .

RTOS in general are way above my programming abilities in general so you could be right that seeing chibiOS as a limitation is incorrect. The main questions I ran into were, when I looked at various motor control MCUs from Ti, Infineon, analogue devices and NXP (stm seems to just be letting the F3 series rot with no replacement or update) none of them appeared to have openOCD support, it seemed like that was required for chibiOS I think. Then there was the question of non-standard peripherals most of them had specialized PWM, ADC and hardware based sigma-delta I couldn't find any examples of chibiOS ports using any of these features so I was unsure if it would get in the way. Using them sounds terribly hard but for the most part since they were intended for motor control to begin with I found they all generally came with low level code examples ready to go for FOC motor control so typically you have 3 synchronized PWM in centre aligned mode with interrupts set up to trigger the ADC. I'm unsure due to lack of programming experience but it seemed as though having to deal with chibiOS would mean I had to scrap the majority of provided code. Though they are pretty generous with low level code, releasing it under BSD or apache when it comes to the actual FOC algo, sensorless obervers, motor detection and speed / current control PID you're either on your own or they're trying to sell you some proprietary code which is closed, impossible for users to change and somehow typically vastly inferior to the VESC despite a team of paid engineers working on it constantly.

arvidb
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Initialisation of the STM32F4 pins that your IMU is connected to, as well as any initialisation required by the IMU itself, would be placed in app_<name>_start() in applications/app_<name>.c, where <name> is a name of your choosing. If the IMU was very complicated to setup/use you could place device-specific code in a separate file and call it from app_<name>_start().

In app_<name>_start() you would also create and start a thread that would run your control algorithm (read IMU data, run your PID controller, tell the VESC what current to use by calling mc_interface_set_current(), and then sleep for a little while). Look at e.g. applications/app_ppm.c for an example. This whole process it greatly simplified by ChibiOS.

You could either replace <name> with "custom" and set custom app in VESC Tool, or modify app.c to start an app with a name of your choosing.

Regarding openocd, that's the program used to upload the binary image to the chip (when you run 'make upload'). I don't think it's required to build/use ChibiOS (or the VESC firmware altogether)?

benjamin
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It's exactly because it's so deeply connected that it would be worthwile extracting it. It would be a PITA to do, but it would make the code much clearer and easier to maintain.

But I digress; I can see you're not convinced. :)

Yes, I'm not convinced :-)

The foc hall sensor table is only relevant to my particular foc implementation, and not very useful in general. It is not even useful for my particular bldc implementation. Moving my foc hall sensor implementation into a seperate file would only reduce mcpwm_foc with a few lines, and add more code in total to glue everything together.

I know it isn't implemented as an externally accessible control mode, but isn't this pretty much the "handbrake" mode? I.e. run the motor openloop with a specified current (and phase). Or put othwerwise: both handbrake and sensor detection could be run through the same set_phase() method.

Yes, the hall sensor detection would work with an extended version of the hand brake (not only the phase, it also sets the current in the D axis instead of the Q axis), but the encoder detection for example requires much more. If I find a reason to make a handbrake function with control over the phase and both the D and Q axis currents, I might make an interface for that and make the hall sensor detection use it. Though I think that adding the axis to the handbrake function would only make it unneccessarily confusing to be used from apps.

Yes, I can see now the rationale behind keeping all the configuration data in one place. Thanks for making that clear to me. It is unfortunate however, since it lands us in the exact opposite corner of the data encapsulation paradigm (object orientation) which is considered good practice (and for good reasons!). It would probably have been better to encapsulate data and have each object supply its own defaults as well as serialise it for flash storage. But it's always easy to be wise after the event...

I don't agree here at all...

Yes, mcpwm could handle its own settings, mcpwm_foc could handle its own settings, mcinterface, encoder etc. as well. There is also a lot of overlap, which would lead to duplicate settings between the modules. Then serialization and deserialization could be handled with them separately, and the communication protocol would handle them separately with a bunch of new commands, and VESC Tool would handle them seperately or semi-seperately. Implementing that is a huge amount of work, and I think it would make dealing with vesc tool, the communication protocol and storing/sharing of settings more complicated with no real benefits.

Right now the settings are connected to a particular motor, which might be a DC motor or a PMSM motor driven by BLDC or FOC with or without different types of sensors. The different modules responsible for driving the motor have to look at the relevant settings for them. Not all settings are relevant for all modules, but there is a lot of overlap (current limits, temperature limits, voltage limits etc.). The settings don't store any state from mcpwm or mcpwm_foc either, they only tell them how to update their own state, which is stored in them internally. For example, the observer uses the settings to determine how and with which gains to update its state in every iteration.

To me this is a perfectly reasonable and sensible implementation. All settings that are related to the motor are stored in one place, and can be shared with all hardware that can be used to drive that motor. When I export settings from VESC Tool, I don't want to export combinations of 10 or so different structures, all related to which motor and sensors I'm using. The current structure is by far not where I would start refactoring things.

In my experience, C variables that are declared to be visible within an entire compilation unit (.c file) and have the same lifetime as the program, are considered global (i.e. they don't have to have external linkage). But regardless of terminology, IMO the fact that these variables are "globally accessible within that file" is an important part of what makes it so hard to see what's going on.

The static variables in mcpwm_foc module represent the state the motor in the view of that module, and the state of operation of the module itself. Internally the module keeps track of and updates its own state, and from the outside it provides interfaces for affecting its operation and reading relevant parts of the state in a general way. I see mcpwm_foc as one single module. Changing how it behaves internally requires deep knowledge of how it works, but that is the nature of the problem itself. Some of the state can probably be put into structures to make it a bit more clear, but I don't see anything major that I would change right away. When I'm working with the file I feel comfortable with it, and few times things get broken when I make updates. Also keep in mind that mcpwm_foc has A LOT more details and corner cases than literature about FOC and code examples usually provide, which naturally makes it more complicated to follow. For example, changing how duty cycle is controlled affects the PID speed controller when the speed reference is 0 which relies on a certain behavior, regardless if it is in the same file or abstracted away somewhere else. This kind of knowledge about nature of the problem itself is required by anyone dealing with the deepest parts of the algorithms.

By the way, one thing that could be split out is access to the hardware, but that is quite a bit of work and some things, such as the very hardware-specific inductance measurement, is not clear where to put. This does not have high priority now, but I could probably do it in a day or two.

benjamin
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@lizardmech

Regarding the IMU, the firmware will get support for it soon with a software I2C implementation to support an MPU6050, MPU9150 or MPU9250 on any two pins. A quaternion filter will also be implemented in the firmware, so that all relevant angles can be read out easily from apps.

lizardmech
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Using the same example and app_nunchuk.c as its the closest example.

https://github.com/vedderb/rise_sdvp/blob/master/Embedded/RC_Controller/...

https://github.com/vedderb/rise_sdvp/blob/master/Embedded/RC_Controller/...

https://github.com/vedderb/bldc/blob/master/applications/app_nunchuk.c

Take mpu9050.c for example and the header include mpu9150.h, would you just relocate mpu9150.h to the applications folder along with the app? Ignoring the other includes say I replaced most of app_nunchuk.c with the code from mpu9050.c and then want to go on to writing kalman filters + the inverted pendulum PIDs, do I have to give each of those their own threads and memory allocation?

The openOCD thing is just one of many chibiOS unknowns, I'm only going off developer posts from their forum where they said they couldn't start a port until openocd was working, another time it looked like it took the main devs 12+ months to get it running on STM32F7s which made me skeptical of portability. Perhaps aside from firmware flashing these things aren't a big deal on the VESC and it's only using a small section of chibiOS but this creates the problem I mentioned earlier, there's realistically no easy way to find out besides asking Benjamin which takes up his limited time, not to mention explaining stuff constantly is annoying and makes the project more of a chore. There's only one Benjamin while there's millions of people who can write C code for MCUs. If you had a task which would take 1 hour coding but required asking Benjamin questions vs 10 hours but is completely self sufficient, the latter is actually the better option. You can always get more people to help with programming but the amount of time Benjamin can spend on the VESC and help is fixed and can't be increased. 

lizardmech
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Regarding the IMU, the firmware will get support for it soon with a software I2C implementation to support an MPU6050, MPU9150 or MPU9250 on any two pins. A quaternion filter will also be implemented in the firmware, so that all relevant angles can be read out easily from apps.

Very nice, thanks for adding that to it.

arvidb
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Benjamin:

Yes, splitting up the config data while preserving the current code layout would be quite senseless. :)

Also I'm not saying there should be a "generic" hall sensor implementation - I'm arguing that encapsulating its data and implementation would be useful for the sake of code clarity. (I do think encapsulation of other things, like PID controllers, might bring further benefits of generalisation, even if they are used a bit differently in different places.)

I think, what I'm really trying to say is, that mcpwm_foc could be split up into several separate modules ("pid_speed", "sensor_hall", "sensor_observer", "pwm", etc.). The interactions could be extracted and implemented in other modules ("sensor_combined", "foc" - this latter would get the phase from sensor_combined->get_phase() and call something like pwm->set_phase()). (And I realise my example is simplified.) This would make the interactions explicit, and separate them from the implementation of the previous modules. And "pwm" here would be "general" in the sense of being useful for all different control modes as well as when detecting sensors and motor resistance; an app writer could use it if necessary, or use the higher level interface foc->set_current(), or the even higher pid_speed->set_speed().*

That is, split up the "nature of the problem" into smaller parts that are easier to grasp. Like the Unix philosophy of composability instead of monolithic design.

I'm not saying this is easy to do, and if you're comfortable working with the code as it is today then I can very well understand that it's not a high priority. Still, I think it could be very worthwhile if you want the project to "take on a life of its own" also on the software side.

I think I will stop trying to argue my point for now as to not waste both our times. If I ever manage to find the time & energy to show in practice that this works and have benefits, I'll bring it up again. :)

*I'm using "module->method" here to mean "a method belonging to that module"; the actual function name would be something like module_method() of course, since it's C we're talking about. :)