Hi John, thanks for your suggestion. What frequency can I expect using this method? I need at least a 1MSPS sampling rate. Also, do you have any code example of this? I tried googling it but I didn't find what I was looking for.
Many thanks On Saturday, January 24, 2015 at 12:52:29 AM UTC, john3909 wrote: > > Why don’t 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...@gmail.com <javascript:>> > Reply-To: "beagl...@googlegroups.com <javascript:>" < > beagl...@googlegroups.com <javascript:>> > Date: Friday, January 23, 2015 at 10:45 AM > To: "beagl...@googlegroups.com <javascript:>" <beagl...@googlegroups.com > <javascript:>> > 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...@googlegroups.com <javascript:>. > 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.
