Ah. I probably should have read the PWM docs a little closer. I guess I
can start writing code since I’m in “waiting for shipping-land”.
Is there much penalty for 32 bit math?
When I enable “Edge aligned PWM” with the interrupt flag on, is the first
interrupt actually the very first sync (of the initial values loaded into
OCxR prior to enable)? Or am I off-by-one here?
Pseudocode:
#define NR_CHANNELS 8
#define FRAME_PERIOD (frame_period_ns/clk_period_ns)
#define PULSE_WIDTH (pulse_width_ns/clk_period_ns)
unsigned long clk_period_ns = 500; // 2MHz; max period is ~32mS
unsigned long frame_period_ns = 22000000; // or NR_CHANNELS * 2ms + 4ms?
unsigned long pulse_width_ns = 500000; // 0.5ms
unsigned int idx;
unsigned int acc; // accumulator
unsigned int pulse_period[NR_CHANNELS];
setup() {
setup stuff;
idx = 0;
acc = 0;
OC1R = PULSE_WIDTH;
OC1RS = pulse_period[idx];
enable PWM;
}
OC1_int() {
// width/period registers are buffered and will be loaded on next sync
if (idx >= NR_CHANNELS) {
idx = 0;
acc = 0;
}
else {
acc += pulse_period[idx++]; // Am I accumulating an error too?
}
if (idx < NR_CHANNELS) {
OC1RS = pulse_period[idx];
}
else if (idx == NR_CHANNELS) {
OC1RS = FRAME_PERIOD - acc;
} // You're watching the "Pad Channel"
}
On Thursday, January 23, 2014 11:27:58 AM UTC-6, Ytai wrote:
>
> This has not yet been implemented. You don't need a timer I believe as the
> OC modules have dedicated timers and in PWM mode will have shadow registers
> for updating the duration with no jitter. 500us is plenty of time at 16MHz
> if you use a high interrupt priority.
> On Jan 23, 2014 12:02 AM, "GoatZilla" <[email protected] <javascript:>>
> wrote:
>
>> I noticed there was an earlier thread about PPM output being a
>> possibility, but I don't see it being implemented yet. Am I reading that
>> right?
>>
>> It does look like it's possible to do with the hardware compare (is
>> Timer2 still free?), as long as the interrupts get serviced within the
>> shortest pulse timing... Which is a ~500uS pulse with 500uS until next
>> pulse.
>>
>> That sounds kind of tight with the way the double comparator only
>> interrupts on the falling edge, so maybe two single comparators -- one for
>> all the rising toggles, and one for all the falling toggles? Or perhaps
>> more?
>>
>>
>>
>>
>>
>>
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