Pada Selasa, 28 Oktober 2014 01.39.00 UTC+8, Nic Cyn menulis:
> 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);
> }
World Bank
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