I've forgotten to mention. I am sending the clocks from the PRU 1 to PRU 0
at this time. So I know exactly how many clocks there is and the frequency.
The objective is to plug the sensor which I want to read the data after
having this working .
-- Fred Gomes
<fred.p.gome...@gmail.com> escreveu no dia terça, 4/12/2018 à(s) 09:25:
> Hi, I need your help,
>
> I need to read data of an SPI Master device on the BeagleBone. Since the
> SPI kernel driver doesn't support an SPI slave mode I have to implement it
> in the PRU (Because the maximum frequency one BeagleBone's GPIO can be
> toggle is only 15 KHz).
> From what I have read, the PRU cycle time is 200 MHz, even so, I can't
> read data up to 10 MHz. I am doing the following:
>
>
>
> k=0;
> shift = 0;
>
> while((__R31&cs) != cs){ // CS = 0
> while((__R31&sclk) == sclk);
> while((__R31&sclk) == sclk){ //sclk = 1
>
> if((__R31&cs) == cs)
> goto END;
> }
> while((__R31&sclk) != sclk); //SCLK = 0
> buffer[cnt] = ((__R31&miso) == miso)? buffer[cnt] | 0x01 << shift:
> buffer[cnt]; // Here is where my cycle is being stranded!!!
> k++;
> shift = (shift==32)? 0 : shift + 1;
> cnt = ((k%32)==0)? cnt+1 : cnt;
>
> If I comment on the reading line, I can't catch clocks at 20 MHz. However,
> if a uncomment it I only can get all of them at 9 MHz (I need 10 MHz). My
> question is if it is possible to get it a bit faster. I can't understand
> why it is so slow (given that the PRU is a real-time processor and has
> a high speed between instructions).
>
> Regards,
> -- Fred Gomes
>
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