Accessing flash directly from User Space
Jonathan.Haws at sdl.usu.edu
Wed Oct 28 09:24:53 EST 2009
> >>> How can I get that pointer? Unfortunately I cannot simply use
> >> address of the flash. Is there some magical function call that
> >> gives me access to that portion of the memory space?
> >> $ man 2 mmap
> >> You want MAP_SHARED and O_SYNC.
> > To use that I need to have a file descriptor to a device, do I
> not? However, I do not have a base flash driver to give me that
> file descriptor. Am I missing something with that call?
Okay, I now have access to the flash memory, however when I write to it the writes do not take. I have tried calling msync() on the mapping to no avail. I have opened the fd with O_SYNC, but cannot get things to work right.
Here are the calls:
int fd = open("/dev/mem", O_SYNC | O_RDWR);
uint16_t * flash = (uint16_t *)mmap(NULL, NOR_FLASH_SIZE,
(PROT_READ | PROT_WRITE), MAP_PRIVATE, fd,
When I do flash = 0x1234, and then check the value, they do not match.
flash = 0x1234;
msync(flash, NOR_FLASH_SIZE, MS_SYNC | MS_INVALIDATE);
printf("flash = %#04x\n", flash);
That prints flash = 0x7f45. I have verified that I am reading the correct values. I can display the flash contents in U-Boot and 7f45 is what is in the first 16 bits of flash.
Why can I not write to flash? What am I doing wrong?
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