Linux/AM4376: PRU access of some McSPI fails

Hello Annette, 

This is the test code I used. I was able to replicate your error if I tried reading from the registers prior to enabling the clocks.

#include <stdint.h>
#include <pru_cfg.h>
#include "resource_table_empty.h"

#define PCRM_CM_PER_SPI0_CLKCTRL    (*((volatile unsigned int *)0x44DF8D00))
#define PCRM_CM_PER_SPI1_CLKCTRL    (*((volatile unsigned int *)0x44DF8D08))
#define PCRM_CM_PER_SPI2_CLKCTRL    (*((volatile unsigned int *)0x44DF8D10))
#define PCRM_CM_PER_SPI3_CLKCTRL    (*((volatile unsigned int *)0x44DF8D18))
#define PCRM_CM_PER_SPI4_CLKCTRL    (*((volatile unsigned int *)0x44DF8D20))

#define McSPI0_HL_HWINFO    (*((volatile unsigned int *)0x48030004))
#define McSPI1_HL_HWINFO    (*((volatile unsigned int *)0x481A0004))
#define McSPI2_HL_HWINFO    (*((volatile unsigned int *)0x481A2004))
#define McSPI3_HL_HWINFO    (*((volatile unsigned int *)0x481A4004))
#define McSPI4_HL_HWINFO    (*((volatile unsigned int *)0x48345004))

/* functions */
void init_spi();
void test_spi();

int main(void)
{
    /* allow OCP master port access by the PRU so the PRU can read external memories */
    CT_CFG.SYSCFG_bit.STANDBY_INIT = 0;
    
    /* initialize the 5 McSPIs */
    init_spi();

    /* try to read offset 0x4 (HW info) from each SPI */
    test_spi();

} 

/* 
 * Init McSPIs
 */
void init_spi(){

    /* Enable clock for SPI0: PRCM_CM_PER_SPI0_CLKCTRL */
    while(!(PCRM_CM_PER_SPI0_CLKCTRL == 0x02)){
        PCRM_CM_PER_SPI0_CLKCTRL = 0x02;
    }

    /* Enable clock for SPI1: PRCM_CM_PER_SPI1_CLKCTRL */
    while(!(PCRM_CM_PER_SPI1_CLKCTRL == 0x02)){
        PCRM_CM_PER_SPI1_CLKCTRL = 0x02;
    }

    /* Enable clock for SPI2: PRCM_CM_PER_SPI2_CLKCTRL */
    while(!(PCRM_CM_PER_SPI2_CLKCTRL == 0x02)){
        PCRM_CM_PER_SPI2_CLKCTRL = 0x02;
    }

    /* Enable clock for SPI3: PRCM_CM_PER_SPI3_CLKCTRL */
    while(!(PCRM_CM_PER_SPI3_CLKCTRL == 0x02)){
        PCRM_CM_PER_SPI3_CLKCTRL = 0x02;
    }

    /* Enable clock for SPI4: PRCM_CM_PER_SPI4_CLKCTRL */
    while(!(PCRM_CM_PER_SPI4_CLKCTRL == 0x02)){
        PCRM_CM_PER_SPI4_CLKCTRL = 0x02;
    }
}

/* 
 * Test if McSPIs can be read
 */
void test_spi(){
    unsigned int test;
    test = McSPI0_HL_HWINFO;
    test = McSPI1_HL_HWINFO;
    test = McSPI2_HL_HWINFO;
    test = McSPI3_HL_HWINFO;
    test = McSPI4_HL_HWINFO;
}

Let me know if there's anything further that is needed, 

Nick