Getting Beaglebone PRUs to work using PASM - beagleboneblack

Question

I have been trying to get the PRU to work in a way that makes sense to me and at this point I am completely clueless. I can get the examples to work, but anytime I make a change or try to write things from scratch I just beat my head against the wall. I just want to as a start access any of the USRLEDS and turn them off or on at some speed, or as first pass turn on a LED and leave it on. Here is a PASM code I got off the internet (Will post link when I find it):
.origin 0
.entrypoint START
#define PRU0_ARM_INTERRUPT 19
#define AM33XX
#define GPIO1 0x4804c000 //Trying to access the GPIO1
#define GPIO_CLEARDATAOUT 0x190 //writing 1 to the bit you want cleared in GPIO_DATAOUT register (what does that mean?)
#define GPIO_SETDATAOUT 0x194 (set a value for GPIO output pins, which pins am I even writing to? GPIO1?
#define GPIO_OE 0x134 //enable the pins output capabilities
START:
//clear that bit
lbco r0, c4, 4, 4 //This creates a constant offset and stores in c4, but why do you need that?
CLR r0, r0, 4 //if you copied the data why do you need to clear it?
SBCO r0, C4, 4, 4 //What is this for?
//MOV r1, 10
MOV r2, 0x00000000 //store address 0x00 into r2, why?
MOV r3, GPIO1 //Store GPIO1 address in r3
MOV r4, GPIO_OE //place address of GPIO_OE into r4
MOV r5, GPIO_SETDATAOUT //store address of GPIO_SETDATAOUT in r5
MOV r6, GPIO_CLEARDATAOUT //store addres of GPIOCLEARDATAOUT in r6
SBBO r2, r3, r4,4 //What is this even doing? Copying 4 bytes from r2 into r3+r4, but why do you want to copy that way and if not why not?
MOV r1, 10
MOV r2, 0xFFFFFFFF //Suppossedly this turn the GPIO1 ON and OFF?
SBBO r2, r3, r6, 4 and again the storage stuff?
HALT
I am also attaching the C code that I am using:
#include <stdio.h>
#include <pruss/prussdrv.h>
#include <pruss/pruss_intc_mapping.h>
#define PRU_NUM 0 //defining which PRU to use
int main() {
int ret;
tpruss_intc_initdata intc = PRUSS_INTC_INITDATA;
//initialize the PRU by using init command from prussdrv.h
ret = prussdrv_init();
if(ret != 0) {
printf("Error returned: %d\n",ret);
printf("PRU unable to be initialized");
return -1;
}
ret = prussdrv_open(PRU_EVTOUT_0);
if(ret != 0) {
printf("Error returned for prussdrv_open(): %d\n",ret);
printf("PRU can't open PRU_EVTOUT_0");
return -1;
}
//Map PRUS's INTC
ret = prussdrv_pruintc_init(&intc);
if (ret != 0) {
printf("Error returned for prussdrv_pruintc_int\n");
printf("PRU doesn't work");
return -1;
}
//load and execute binary on PRU
prussdrv_exec_program(PRU_NUM, "./ashwini_test.bin");
prussdrv_pru_wait_event(PRU_EVTOUT_0);
prussdrv_pru_clear_event(PRU_EVTOUT_0,PRU0_ARM_INTERRUPT);
/*Disable PRU and close memory mappings*/
prussdrv_pru_disable(PRU_NUM);
prussdrv_exit();
//prussdrv_pru_wait_event(PRU_EVTOUT_0);
return 0;
}
I have gone through THE TRM and https://groups.google.com/forum/#!topic/beaglebone/98eF1wQE_QA, and elinux and derekmolloy, I just feel like I am missing something very basic about how address scheme work or how to think about these things. Thanks again for your help!

Answer 1

When you say that's your PASM code... do you mean it's some code you got from somewhere else that you're trying to use? Because the comments on most lines asking what they do makes it seem unlikely that it's actually your code...
Anyways, can't really answer unless you have a specific question, but there's plenty of info out there about how to use the GPIO subsystem on the BeagleBone's AM335x processor. I talked about it some in a post a while back here: https://graycat.io/tutorials/beaglebone-io-using-python-mmap/
I've also got a few documented PRU assembly examples here: https://github.com/alexanderhiam/PRU-stuffs