Specifications

Then the second write begins, but before writing to the second block, the block is erased. At this point,
t(3), the flash contains 4 KB of 0xAA and 4 KB of 0xFF. After the second write finishes, at time t(4), the 2
KB of 0xFF at address 0x1000 is corrupted.
Fine-Grained Flash Access
Three additional functions provide complete control for writing flash contents at the highest granularity:
• alt_get_flash_info()
• alt_erase_flash_block()
• alt_write_flash_block()
By the nature of flash memory, you cannot erase a single address in a block. You must erase (that is, set to
all ones) an entire block at a time. Writing to flash memory can only change bits from 1 to 0; to change
any bit from 0 to 1, you must erase the entire block along with it.
Therefore, to alter a specific location in a block while leaving the surrounding contents unchanged, you
must read out the entire contents of the block to a buffer, alter the value(s) in the buffer, erase the flash
block, and finally write the whole block-sized buffer back to flash memory. The fine-grained flash access
functions automate this process at the flash block level.
#include <stdio.h>
#include <string.h>
#include "sys/alt_flash.h"
#define BUF_SIZE 1024
int main ()
{
alt_flash_fd* fd;
int ret_code;
char source[BUF_SIZE];
char dest[BUF_SIZE];
/* Initialize the source buffer to all 0xAA */
memset(source, 0xAA, BUF_SIZE);
fd = alt_flash_open_dev("/dev/ext_flash");
if (fd!=NULL)
{
ret_code = alt_write_flash(fd, 0, source, BUF_SIZE);
if (ret_code==0)
{
ret_code = alt_read_flash(fd, 0, dest, BUF_SIZE);
if (ret_code==0)
{
/*
* Success.
* At this point, the flash is all 0xAA and we
* have read that all back to dest
*/
}
}
alt_flash_close_dev(fd);
}
else
{
printf("Cannot open flash device\n");
}
NII5V2
2015.05.14
Fine-Grained Flash Access
6-19
Developing Programs Using the Hardware Abstraction Layer
Altera Corporation
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