Why don¹t you use SPI with DMA? DMA is automatically used when the size of transfer exceeds 160 bytes. You would have to create a kernel driver because SPIDEV has too much overhead. The SPI interface can transfer up to 48MHz clock, which is the max clock of the device you want to use.
Regards, John From: touste <baptiste.pier...@gmail.com> Reply-To: "beagleboard@googlegroups.com" <beagleboard@googlegroups.com> Date: Friday, January 23, 2015 at 10:45 AM To: "beagleboard@googlegroups.com" <beagleboard@googlegroups.com> Subject: [beagleboard] Fast ADC using PRU to bitbang SPI > Hi guys, > > I would like to know if someone here has already tried bitbanging SPI with the > PRU units? > > I have a 12bit ADC (TI ADS7883) which takes a clock signal and outputs 12 bits > of data, and I would like to use the PRU to achieve high sampling rate. > > See http://www.ti.com/lit/ds/symlink/ads7883.pdf for the ADC documentation > with the interface timing diagram. > > Basically, the PRU program would do the following (assuming a cycle time of > 5ns and one cycle for each line of the loop): > > - Initiate 3 GPIO channels (2 outputs: SCLK and CS, 1 input: SDO) > - Allocate memory (a lot! I'd like to capture millions of samples) > Loop for N samples: > - Pull CS high > - Wait 3 cycles > - Pull SCLK high > - Wait 2 cycles > - Pull CS low (initiate output) > - Wait 2 cycles > - Pull SCLK low > - Wait 5 cycles > - Pull SCLK high > - Wait 5 cycles > - Pull SCLK low > - Wait 5 cycles > - Pull SCLK high > - Wait 5 cycles > - Pull SCLK low > - Read SDO (first bit) > - Store it somewhere > - Wait 3 cycles > - Pull SCLK high > - Wait 5 cycles > - Pull SCLK low > - Read SDO (2nd bit) > - Store it somewhere > - Wait 3 cycles > - Pull SCLK high > - Wait 5 cycles > - Pull SCLK low > - Read SDO (3rd bit) > - Store it somewhere ... and so on until 12th bit > - Wait 60ns (acquisition time) while always pulling CLK high and low every 6 > cycles > End of loop > > > The problem is that I have never programmed in assembly code. I have tried > looking at examples but have a really hard time understanding the simplest > commands (ex: what is a simple MOV r3, 1<<7 doing?). > > I'd like to have a thoroughly commented, simple example to start if possible. > > Memory issues are also a big problem. How can I store all the captured data so > that it is fast and doesn't overflow the PRU memory? > > Many thanks for your help! > > Touste > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to beagleboard+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
