What is the PWM Groups driver in OpenBeken?
It is a firmware module that lets two hardware PWM units toggle in perfect phase opposition while enforcing a user-defined dead time between transitions [Elektroda, p.kaczmarek2, post #20888311]
PWM Groups (synchronized PWMs) driver for OpenBeken - BK7231N - with dead time
TL;DR
- OpenBeken 1.17.388 adds a BK7231N PWM Groups driver that synchronizes two PWMs, supports independent duty cycles, and inserts a configurable dead time.
- The timings are calculated from the main oscillator frequency, with duty values treated as percentages and frequency treated as Hz.
- A typical command is PWMG_Set 10 10 10 1000, and PinA/PinB use P-index values such as 6 and 7.
- The revised implementation fixes the SDK bugs and works correctly in tests, including when a 0 duty cycle is used.
- Range checking is still missing, and behavior for PWMs outside the same pair has not been tested.
In the 1.17.388 version, OpenBeken introduced a PWM Groups driver. This driver enables the synchronization of two PWMs and facilitates setting a specified dead time between them. Of course, the duty cycles of each PWM groups are independently controlled and the frequency is also adjustable.
Tuya's (Beken?) implementation
The PWM groups driver is present in the used BK7231N SDK, but after few quick tests it's clear that's it not working correctly:
Code: C / C++
There are multiple issues with this code:
- the second duty cycle is not used at all and both PWMs are using duty_cycle1
- the frequency variable is not in fact a frequency, but rather a period
- the following implementation breaks when a 0 duty_cycle is given
My improvements
I've performed some tests with the original version of the code, also by manually setting values for each PWM:
Code: C / C++
Result:
Test code:
Code: C / C++
results:
Test code:
Code: C / C++
Result:
Test code:
Code: C / C++
Result:
It seems that duty_cycle1, duty_cycle2 and duty_cycle3 describes when a PWM toggles self state. Based on that, I proposed the following implementation:
Code: C / C++
The code above still uses the incorrect name for period variable (it's called frequency), but I also resolved it.
The tests have shown that the period and duty cycles should be calculated on the main oscillator frequency basis:
Code: C / C++
The duty values are assumed to be in percent and frequency is in Hz. The period values are calculates from them.
Usage
To use it in OBK, you need a BK7231N device. First, enable driver:
startDriver PWMGThen, start the group:
PWMG_Set 10 10 10 1000
Full command syntax is the following:
PWMG_Set Duty1Percent Duty2Percent DeadTimePercent Frequency PinA PinB
Please note that the following will only work correctly for PWM pairs, like PWM0+PWM1, PWM2+PWM3, etc.
Futhermore, for PinA/PinB you need to give a P-index, so PWM0 is not 0, it's 6.
Please see screenshot below for explanation:
Of course, when typing command, type just "6", not "P6", like:
PWMG_Set 10 10 10 1000 6 7
Examples
Command (1000Hz, 10% first, second 10%, dead 10%):
PWMG_Set 10 10 10 1000
Result:
Command (1000Hz, 50% first, second 10%, dead 10%):
PWMG_Set 50 10 10 1000
Result:
Command (5000Hz, 10% first, second 10%, dead 10%):
PWMG_Set 10 10 10 5000
Result:
Summary
PWM groups driver is now working, altough it still could be improved a bit. For example, the code is not currently checking for out of range values, and using them may yield unexpected results. Futhermore I have not tested how PWM behaves when user specified two PWMs that are not from the same group.
The PWM groups driver was added per user request here, but I hope it can be useful for more people as well. Do you have any ideas how could you use such a driver? Let us know.
p.kaczmarek2 wrote 14232 posts with
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Comments
Thank you very much for creating the driver. I will test it in my project and report here. [Read more]
You're welcome, I think I will still take some time tomorrow to improve it futher, because with the current state of things, it's possible to "break" dead time by setting too high duty cycles for both... [Read more]
Hello, Unfortunately, I've only recently gotten around to testing the new function again. I flashed a PEARL light chain ZX-5140-675 with Open Beken. See also my query here: https://www.elektroda.com/rtvforum/viewtopic.php?p=20840633#20840633 The... [Read more]
That's a good news! What do you mean by "centrally"? You can script the device behaviour in autoexec.bat, see samples: https://github.com/openshwprojects/OpenBK7231T_App/blob/main/docs/autoexecExamples.md You... [Read more]
By central I meant like an LED light bulb, an on/off switch and sliders for flashing frequency and light/dark. I prefer the control directly via OpenBeken. [Read more]