mmap on Virtex-II Pro

Joshua Lamorie jpl at
Sun Jan 30 11:54:41 EST 2005

Gidday there,

I have Linux running on a Virtex-II Pro system (with a second FPGA 
connected by a custom OPB/PLB bridge).

I have a device on the OPB bus that I want to provide to applications 
through mmap.  However, with my current implementation there are some 
strange behaviours.

If I mmap in my application, I can read everything in the device memory 
(in blockram and other registers) with no problems.
However if I write only a few bytes, they don't seem to go through to 
the memory area, and instead some of the memory is cleared.  When I 
write a large number of values (e.g. the counter in a for loop).  The 
values show up, but the first 4 bytes are missing, and it only writes 
every other 4 bytes.  For example...

0000:0000 | 04 05 06 07 00 00 00 00 0c 0d 0e 0f 00 00 00 00
0000:0010 | 14 15 16 17 00 00 00 00 1c 1d 1e 1f 00 00 00 00

I'm using Rubini's Linux Device Drivers 2nd edition as a reference and 
inside the mmap function of my module I simply do

remap_page_range(vm_start,physical_address, vm_end-vm_start,vm_page_prot)

I did a quick search through the archives and I noticed that there was a 
call io_remap_page_range but that is just a macro pointing to 
remap_page_ranger.  I also noticed that pgprot_noncached was used in a 
64 bit instance, but that doesn't exist in my kernel.

I'm using 2.4.26, probably almost a year old now.

Are there any simple examples of mapping OPB memory to user space?

I'm also setting a couple of vm_flags such as VM_IO and VM_RESERVED.  
Could there be a magic one that I'm missing?  I know that there are some 
elements of the busses connected to the PPC405 in the Virtex-II Pro that 
are 64-bit... is it possible that I'm mapping a 64-bit area and nothing 
is correctly written?

Thanks in advance for any advice.



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