Linux on Xilinx v2pro: OCM access?

Peter,

here is some user code that let's you access the DOCM (8KB at address

--- // mmaptest.c // gcc -o mmaptest mmaptest.c // su -c "mmaptest"

#include #include #include #include #include

int main(void) { int fd; unsigned char *buf; int i;

fd=open("/dev/mem", O_RDWR); printf("fd: %d\n", fd);

buf = mmap (0x40000000, 8*1024, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0x40000000); printf("buf: %x\n", buf); assert(buf == 0x40000000); // virtual address must match physical address

for (i=0; i < 8; i++) printf("buf[%d] = %x\n", i, buf[i]);

return 0; }

---

Please note that the OCM is virtually addressed and virtually accessed, i.e. you must make sure that the virtual address returned by mmap() is exactly the same as the physical address. For that, ioremap() will not work as the virtual address and the physical address typically are different.

Further, you have to enable the work-around for the OCM errata, i.e. set some undocumented bit(s) in the CCR0 register. The PPC405 errata sheet available from xilinx.com contains information which bit(s) these are (see solution record 14052).

Next, the program must be run with enough rights to access /dev/mem, i.e. run it as root. For a final implementation you will typically have to write a device driver that accesses the OCM and abstracts these accesses from the user code.

- Peter

Peter M> I'm having trouble accessing OCM peripherals from Linux.

Thank you *very much*. It works perfectly now.

I imagine the MMU is on the PLB-facing side of the PPC, so that address translation is not active for cache-like entities like OCM. But I would not have guessed this without help.

Xilinx hotline support is pretty reasonable, but Usenet can sometimes outperform it :-).

Cheers, Peter Monta RGB Networks, Inc.