GPT Jitter

Discussions and support about ChibiOS/HAL, the MCU Hardware Abstraction Layer.
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Re: GPT Jitter

Postby jscott » Mon Feb 29, 2016 9:56 pm

AH.... Yes, not a great solution. You end up with a really long time that your processor is tied up doing nothing but looking at its watch and waiting for something to happen...

So with PWM you will select your time and just change the frequency on each output bit. you might try 0hz for off, then what ever you want for your 0-bit and 1-bit.

Then the hardware timer handles generating your 1/0 square wave signal and you only have to pay attention every 0.8ms.

WAY easier! Plus, if you really need to save every possible mwH, you might be able to research low power mode during idle.
That is a lot of work getting it sorted out however.

Another thought is that you might be able to run the '429 at a lower clock rate. Depending on what else this processor is doing, you might be able run run it under 100Mhz.


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Re: GPT Jitter

Postby A319 » Mon Feb 29, 2016 10:12 pm

Well... it's not that easy, because I take care about the Phase. Just switching the PWM frequency would bring it out of phase. The modulation could still work, but it would be way worse. The AFSK frequencies are at 1200Hz and 2200Hz. But it should be still possible.
I just checked, if one of the two GPIO pins (connected to the transmitter) can be used for PWM. But I'm lucky. :D ... ch_mpu.png
I connected radio 1 to PA9 and PA10.
Radio 2 is connected to PE13 and PE14.
So I can use either GPIO0 or GPIO1 of the radios.


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