Memory map?

Hello,

After booting kernel, I want to access the physical address in rom , for example:
my rom begins at 0xFE00 0000, and I want to read 1 byte at this address.

currently, the MMU has been turned on, the RAM begin at 0x0C00 0000, and I don't know what the address of the ROM is.

what do I have to do?
is there anybody know how to take the address of the ROM?

Help me, pls.
Thank you,
Jari

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When exactly do you want to do this, is it in the kernel or by an application, and what kind of system are you using? There are many ways to do this....

	-- Dan

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Jari,
I take it you're trying to do this from an application (i.e. not within the kernel). Here is a (hack) piece of code which performs a similar task. I use it to access a dual-port RAM connecting me to another processor. First, it needs access to the (860T)'s internal memory map, to set up the chip selects so that CS5 decodes at 0x50000000. Then it gets a pointer I can use to access the memory. You probably only need to do the last mmap (and the fopen of /dev/mem!), since (presumably) there are already chip selects decoding your ROM. (additional comments after the code)

#include <stdio.h>
#include <asm/io.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#include <unistd.h>
#include <sys/mman.h>
#include <errno.h>

char *MapDpRam(void)
{
int *paddr1;
char *paddr2;
int fd;
// figure out the page size (since we can only mmap in pagesize
increments)
size_t size = getpagesize();
// get an FD to /dev/mem
fd = open("/dev/mem",O_RDWR);
// these 3 lines change the internal chip-selects in the 860T paddr1 = mmap(0,size,PROT_READ|PROT_WRITE,MAP_SHARED,fd,0xfa200000); *(paddr1+0x4b) = 0xffff8d84;
*(paddr1+0x4a) = 0x50007401;
// done messing with chip-selects, unmap them munmap(paddr1,size);
// this one does the real work, gives me a pointer which, when accessed,
points to the memory at physical address 50000000
paddr2 = mmap(0,size,PROT_READ|PROT_WRITE,MAP_SHARED,fd,0x50000000); return(paddr2);
}

Notes: It's a bit sloppy, I assume that getpagesize() returns at least 1K (which is all I need). If you need more space, you will have to set "size" to some multiple of pagesize that's big enough. It also assumes it knows where the MCR points to (0xfa200000) rather than reading it directly (I'm too lazy to figure out how to do that! :)
Hope it helps...

Mark Phillips

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