I am trying to access, via mmap on /dev/mem, the GPIOs at addresses
0x44e07000, 0x4804c000, 0x481ac000 and 0x481ae000. These are GPIO banks
0,1,2 and 3 respectively.
Access is successful on GPIO bank 0 and 1 (0x44e07000 and 0x4804c000) but
fails consistently with a "Bus Error" on GPIO bank 2 and 3 (0x481ac000 and
0x481ae000).
Does anybody have any idea why this might be happening? Sample C code which
reproduces the error below - basically it is trying to read the
GPIO_REVISION at offset 0 at the start of each GPIO bank. The expected
value returned should be 0x50600801 - but a "Bus Error" is returned for
GPIO banks 2 and 3.
This seems to happen on standard 3.8.13-bone47 on a BBB rev C right out of
the CircuitCo box and also on an 3.14 ubuntu kernel.
I would really appreciate any insights you may have
// c code to test access to the /dev/mem file
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>
#define GPIO_BANK_0 0x44E07000
#define GPIO_BANK_1 0x4804C000
#define GPIO_BANK_2 0x481AC000
#define GPIO_BANK_3 0x481AE000
int gpio_mmap_test(int gpioBank, int sizeToFetch);
int main()
{
gpio_mmap_test(GPIO_BANK_0, 0xfff);
gpio_mmap_test(GPIO_BANK_1, 0xfff);
gpio_mmap_test(GPIO_BANK_2, 0xfff);
gpio_mmap_test(GPIO_BANK_3, 0xfff);
return 0;
}
int gpio_mmap_test(int gpioBank, int sizeToFetch)
{
int gpio_fd2 = open("/dev/mem", O_RDWR | O_SYNC);
if (gpio_fd2 < 0)
{
printf("Could not open GPIO memory fd\n");
return 0;
}
volatile ulong *gpio;
gpio = (ulong*) mmap(NULL, sizeToFetch, PROT_READ | PROT_WRITE,
MAP_SHARED, gpio_fd2, gpioBank);
if (gpio == MAP_FAILED)
{
printf ("GPIO Mapping failed\n");
close(gpio_fd2);
return 0;
}
// offset 0 is the GPIO_REVISION field
// expected value is 0x50600801
int gpioRevision = gpio[0];
printf("bank %04x, gpioRevision = %04x\n", gpioBank, gpioRevision);
close(gpio_fd2);
}
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