NRF51822 generate pulse with GPIO

RE: NRF51822 generate pulse with GPIO

zn — Fri, 14 Jul 2017 07:04:33 GMT

I am also thinking about this. And probably this is the easiest way to do it.

RE: NRF51822 generate pulse with GPIO

RK — Thu, 13 Jul 2017 20:21:20 GMT

If you just want one pulse of <.3us I'd just write my own 4 lines (or so) of assembly to do it.

RE: NRF51822 generate pulse with GPIO

zn — Thu, 13 Jul 2017 13:34:11 GMT

This makes sense. So the assembly looks like this:

117       	*addrPinClr = PIN_MASK;
000213be:   ldr     r3, [r7, #8]
000213c0:   movs    r2, #128        ; 0x80
000213c2:   lsls    r2, r2, #9
000213c4:   str     r2, [r3, #0]
118       	*addrPinSet = PIN_MASK;
000213c6:   ldr     r3, [r7, #12]
000213c8:   movs    r2, #128        ; 0x80
000213ca:   lsls    r2, r2, #9
000213cc:   str     r2, [r3, #0]

Haven't got any good idea that how to generate a single pulse with PPI. Any suggestions?

RE: NRF51822 generate pulse with GPIO

zn — Thu, 13 Jul 2017 12:41:06 GMT

Actually I don't want to generate a PWM, but instead a single pulse with width less than 0.3us. And the example code is only for test what's the fastest toggling speed.

RE: NRF51822 generate pulse with GPIO

Sigurd — Thu, 13 Jul 2017 07:52:30 GMT

Hi,

You need to use GPIOTE and PPI to achieve a 50% duty PWM with 8MHz.

You can find code example for that in this post.

RE: NRF51822 generate pulse with GPIO

RK — Thu, 13 Jul 2017 03:53:32 GMT

If you go look at the assembly code that generates I suspect you'll find that the loop is about 6 instructions long. 6/16,000,000 = 3.75us. Toggling the pin like that isn't going to work, you need PPI.

One line of C != one assembly instruction

oh and try optimisation, but put

uint32_t volatile * addrPinSet ..

to stop the loop getting optimized out (or use the proper CMSIS macros)