I'm kinda new to the beaglebone black world running on a AM335X Cortex A8 processor and I would like to use the PRU for fast analog read with the maximum sampling rate possible.
I would like to read all 7 inputs in a loop form like:
while( n*7 < sampling_rate){ //initial value for n = 0
read(AIN0); //and store it in shared memory(7*n + 0)
read(AIN1); //and store it in shared memory(7*n + 1)
read(AIN2); //and store it in shared memory(7*n + 2)
read(AIN3); //and store it in shared memory(7*n + 3)
read(AIN4); //and store it in shared memory(7*n + 4)
read(AIN5); //and store it in shared memory(7*n + 5)
read(AIN6); //and store it in shared memory(7*n + 6)
n++;
}
so that I can read them from a host program running on the main processor. Any idea how to do so? I tried using a ready code called ADCCollector.c from a package named AM335x_pru_package but I can't figure out how to get all the addresses and values of the registers used.
This is the code I was trying to modify (ADCCollector.p):
.origin 0 // offset of the start of the code in PRU memory
.entrypoint START // program entry point, used by debugger only
#include "ADCCollector.hp"
#define BUFF_SIZE 0x00000fa0 //Total buff size: 4kbyte(Each buffer has 2kbyte: 500 piece of data
#define HALF_SIZE BUFF_SIZE / 2
#define SAMPLING_RATE 1 //Sampling rate(16khz) //***//16000
#define DELAY_MICRO_SECONDS (1000000 / SAMPLING_RATE) //Delay by sampling rate
#define CLOCK 200000000 // PRU is always clocked at 200MHz
#define CLOCKS_PER_LOOP 2 // loop contains two instructions, one clock each
#define DELAYCOUNT DELAY_MICRO_SECONDS * CLOCK / CLOCKS_PER_LOOP / 1000 / 1000 * 3 //if sampling rate = 98000 --> = 3061.224
.macro DELAY
MOV r10, DELAYCOUNT
DELAY:
SUB r10, r10, 1
QBNE DELAY, r10, 0
.endm
.macro READADC
//Initialize buffer status (0: empty, 1: first buffer is ready, 2: second buffer is ready)
MOV r2, 0
SBCO r2, CONST_PRUSHAREDRAM, 0, 4
INITV:
MOV r5, 0 //Shared RAM address of ADC Saving position
MOV r6, BUFF_SIZE //Counting variable
READ:
//Read ADC from FIFO0DATA
MOV r2, 0x44E0D100
LBBO r3, r2, 0, 4
//Add address counting
ADD r5, r5, 4
//Write ADC to PRU Shared RAM
SBCO r3, CONST_PRUSHAREDRAM, r5, 4
DELAY
SUB r6, r6, 4
MOV r2, HALF_SIZE
QBEQ CHBUFFSTATUS1, r6, r2 //If first buffer is ready
QBEQ CHBUFFSTATUS2, r6, 0 //If second buffer is ready
QBA READ
//Change buffer status to 1
CHBUFFSTATUS1:
MOV r2, 1
SBCO r2, CONST_PRUSHAREDRAM, 0, 4
QBA READ
//Change buffer status to 2
CHBUFFSTATUS2:
MOV r2, 2
SBCO r2, CONST_PRUSHAREDRAM, 0, 4
QBA INITV
//Send event to host program
MOV r31.b0, PRU0_ARM_INTERRUPT+16
HALT
.endm
// Starting point
START:
// Enable OCP master port
LBCO r0, CONST_PRUCFG, 4, 4 //#define CONST_PRUCFG C4 taken from ADCCollector.hp
CLR r0, r0, 4
SBCO r0, CONST_PRUCFG, 4, 4
//C28 will point to 0x00012000 (PRU shared RAM)
MOV r0, 0x00000120
MOV r1, CTPPR_0
ST32 r0, r1
//Init ADC CTRL register
MOV r2, 0x44E0D040
MOV r3, 0x00000005
SBBO r3, r2, 0, 4
//Enable ADC STEPCONFIG 1
MOV r2, 0x44E0D054
MOV r3, 0x00000002
SBBO r3, r2, 0, 4
//Init ADC STEPCONFIG 1
MOV r2, 0x44E0D064
MOV r3, 0x00000001 //continuous mode
SBBO r3, r2, 0, 4
//Read ADC and FIFOCOUNT
READADC
Another question is: if I simply changed the #define Sampling_rate from 16000 to any other number below or equal to 200000 in the (.p) file, I will get that sampling rate? or should I change other things?
Thanks in advance.
I used the c wrappers from libpruio: http://www.freebasic.net/forum/viewtopic.php?f=14&t=22501
and then use this code to get all my ADC values:
#include "stdio.h"
#include "c_wrapper/pruio.h" // include header
#include "sys/time.h"
//! The main function.
int main(int argc, char **argv) {
struct timeval start, now;
long mtime, seconds, useconds;
gettimeofday(&start, NULL);
int i,x;
pruIo *io = pruio_new(PRUIO_DEF_ACTIVE, 0x98, 0, 1); //! create new driver structure
if (pruio_config(io, 1, 0x1FE, 0, 4)){ // upload (default) settings, start IO mode
printf("config failed (%s)\n", io->Errr);}
else {
do {
gettimeofday(&now, NULL);
seconds = now.tv_sec - start.tv_sec;
useconds = now.tv_usec - start.tv_usec;
mtime = ((seconds) * 1000 + useconds/1000.0) + 0.5;
printf("%lu",mtime);
for(i = 1; i < 9; i++) {
printf(",%d", io->Adc->Value[i]); //0-66504 for 0-1.8v
}
printf("\n");
x++;
}while (mtime < 100);
printf("count: %d \n", x);
pruio_destroy(io); /* destroy driver structure */
}
return 0;
}
In your example you use libpruio in IO mode (synchronous) and therefore you have no control over the sampling rate, since the host CPU doesn't work in real-time.
To get the maximum sampling rate (as mentioned in the OP) you have to use either RB or MM mode. In those modes libpruio buffers the samples in memory and the host can access them asynchronously. See example rb_file.c (or triggers.bas) in the libpruio package.
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