beaglebone black freezes.

kernel-freeze.c

// Tested kernel freeze on Linux beaglebone 4.4.91-ti-r137 

#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>
#include <stdio.h>


// Memory space mapped to the Clock Module registers
#define CM_BASE                 0x44e00000
#define CM_SIZE                 0x4000

// Clock Module Peripheral registers
#define CM_PER_TIMER4_CLKCTRL   (0x000 + 0x88)

#define IDLEST_MASK             (0x03 << 16)
#define MODULEMODE_ENABLE       (0x02 << 0)

#define CLKSEL(x)               (((x) & 0x3) << 0)
#define CLKSEL_CLK_M_OSC        CLKSEL(1)


static void pwm_timers_ena_clk(volatile uint32_t *cm, uint32_t reg, int timer) {
  uint32_t val;

  val = cm[reg/4];
  if (val & IDLEST_MASK) {
    val |= MODULEMODE_ENABLE;
    cm[reg/4] = val;
    do {
      val = cm[reg/4];
    } while (val & IDLEST_MASK);
  }
}

static int pwm_timers_enable_clocks(int fd) {
  volatile uint32_t *cm = (volatile uint32_t*) mmap(0, CM_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, CM_BASE);
  if (cm == MAP_FAILED) { perror("mmap() CM"); return 0; }

  // Enable the timer clocks
  pwm_timers_ena_clk(cm, CM_PER_TIMER4_CLKCTRL, 4);
  return 1;
}

int main(int argc, char *argv[]) {
  int fd = open("/dev/mem", O_RDWR);
  if (fd == -1) { perror("open()"); return 1; }
  pwm_timers_enable_clocks(fd);
  return 0;
}