README: mention the existence of the -l command

Signed-off-by: Sean Cross <sean@xobs.io>
This commit is contained in:
Sean Cross 2019-02-25 13:56:22 +08:00
parent bcbc7319c1
commit 7fb6e4bb7b

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@ -55,4 +55,67 @@ You can verify the SPI flash was programmed with the `-v` command:
## Checking SPI Flash was Written
You can "peek" at 256 bytes of SPI with `-p [offset]`. This can be used to quickly verify that something was written.
You can "peek" at 256 bytes of SPI with `-p [offset]`. This can be used to quickly verify that something was written.
## Patching ROM
`fomu-flash` supports patching ROM. To do this, you must synthesize your bitstream with a fixed random ROM contents. This is so `fomu-flash` has something to look for.
The Python code for this would look like:
```python
def xorshift32(x):
x = x ^ (x << 13) & 0xffffffff
x = x ^ (x >> 17) & 0xffffffff
x = x ^ (x << 5) & 0xffffffff
return x & 0xffffffff
def get_rand(x):
out = 0
for i in range(32):
x = xorshift32(x)
if (x & 1) == 1:
out = out | (1 << i)
return out & 0xffffffff
def get_bit(x):
return (256 * (x & 7)) + (x >> 3)
```
And the corresponding C code looks like:
```c
uint32_t xorshift32(uint32_t x)
{
/* Algorithm "xor" from p. 4 of Marsaglia, "Xorshift RNGs" */
x = x ^ (x << 13);
x = x ^ (x >> 17);
x = x ^ (x << 5);
return x;
}
uint32_t get_rand(uint32_t x) {
uint32_t out = 0;
int i;
for (i = 0; i < 32; i++) {
x = xorshift32(x);
if ((x & 1) == 1)
out = out | (1 << i);
}
return out;
}
static uint32_t fill_rand(uint32_t *bfr, int count) {
int i;
uint32_t last = 1;
for (i = 0; i < count / 4; i++) {
last = get_rand(last);
bfr[i] = last;
}
return i;
}
```
Currently, `fomu-flash` only supports 8192-byte ROMs, though there is no reason why it can't be extended to other sizes.
Specify a ROM to load on the command line with `-l`.