I would like to inform you about my work to make Alex famous MultiWii software a little bit better.
Alex, you did a great job.
Originally I want to optimize the servo outputs only, but by the time it becomes a little bit more.
Then came out:
* PROMINI: 16 bit very low-jitter software PWM for 8 motors + 3 servos.
* MEGA: 16-bit pure hardware PWM - 12 channels, 400Hz. background operation, without IRQ-/CPU load.
* For both: 0.5 us time resolution for normal RX / SUM_PPM Rx.
Spectrum Sat routine extended to 12 channels (both frames used).
Works to reduce Jitter:
Replacement of the API functions for time delays and time measurements (disables all timer0_IRQs)
Some optimations in ISR routines to reduce interrupt time.
Replacement of timer polling code (heavy interrupt blocking cli , sei) by interruptable delay routines.
Here some more in detail:
PWM Promini:Output with 16 bit timer1, 8 channels for motors / 3 channels for servos with software PWM.
Now it is possible to use OCTOs with ProMini plus Camstab and Camtrigger.
There is no distinction made between servos / motors in PWM output handling.
PWM channels are fairly distributed to both Compare Modules A / B.
PWM output is realized in the ISR (TIMER1_COMP? _vect) in a chained method.
In one IRQ call output PWMA_n-1 is set low and PWMA_n is set high. So we have only half of IRQ load as now realized.
We have a resolution of 0.5us in puls lenght.
The repetition rate is due to the process variable and depends on the number of channels in each compare unit and pulse duration.
For a QUADRO with Camstab we have 222Hz@1.5ms.
For the OCTOs with Camstab we have 133Hz@1.5ms.
The accuracy of the pulse length is the most significant parameter. Only these value will be evaluated by the ESC.
The repetition rate determines the dynamic behavior of the copter.
The ISR for compare module A is as follows:
ISR(TIMER1_COMPA_vect) {
static uint8_t state = 0;
if (state == 0) {
PWMA0_lo;
PWMA1_hi;
OCR1A+= PWM_A1;
state++ ;
} else if (state == 1) {
PWMA1_lo;
PWMA2_hi;
OCR1A+= PWM_A2;
state++ ;
if (state == NO_PWMA) state = 0;
} else if (state == 2) {
PWMA2_lo;
PWMA3_hi;
OCR1A+= PWM_A3;
state++ ;
if (state == NO_PWMA) state = 0;
} else if (state == 3) {
PWMA3_lo;
PWMA4_hi;
OCR1A+= PWM_A4;
state++ ;
if (state == NO_PWMA) state = 0;
} else if (state == 4) {
PWMA4_lo;
PWMA5_hi;
OCR1A+= PWM_A5;
state = 0;
}
}
PWM-MEGA:Output with four 16-bit timer1,3,4,5. PWM in pure hardware with PWMwaveform 14.
12 channels total, of which nine channels have 400Hz repetition rate, 3 channels have 32Hz repetition rate.
All PWMs are running in background. No Timer IRQs neccesary. Update is realized with double bufferd compare-registers.
We can write to this registers at any time.
Some smaller topo modification are neccesary for OCTO motors 6,7. Motors 6,7 are moved to the 16-bit ports D11/D12.
It's very easy to change the repetition rates of the PWM triple by tuneing the ICRn values.
API-timer/delay substitute:
API micros() ----> micros16() or micros32()
API millis() ----> millis32
API delay(uint16_t ms) ----> delay0(uint16_t ms)
API delayMicroseconds(uint32_t us) ----> delayMicroseconds0(uint32_t us)
@Alex:
in zip file you find the new mega OCTO configuration (motor 6,7 mod)
and you have the configurations for the OCTO ProMini.
In the excel sheet you see the configuration for Pauls ARDDUINO mega.
My software mod is based on version MultiWii_dev_20120121.
Please push the PWM4-files to the code reviews page.
zip file: http://www.modfly.de/MultiWii/MultiWii_dev_20120121_PWM4.zip
enjoy, dieter
