Accessing flash directly from User Space
scottwood at freescale.com
Wed Oct 28 09:32:13 EST 2009
Jonathan Haws wrote:
> 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?
Flash does not work that way -- you must send it commands to erase a
block, and then further commands to program new data.
It sounds like what you really want is the /dev/mtd or /dev/mtdblock
interface, not raw access to the flash chip.
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