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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