first I want to thank You for Your fast answer. I work on MIPS 4Kec with linux
kernel in version 2.6.15 from linux-mips (gcc 4.0.3 and gcc 3.4.3).
>> There is no byte access to uncached mmaped memory. Is this correct statement?
>Definately wrong. For example alot of mmapped I/O devices use uncached
Ok, in that case I have problem with byte access on mmaped uncached memory.
Reason for previous post is next:
If I write bytes to mmaped uncached memory like:
ptr = (unsigned char*)mmap(0,lineSize,PROT_READ|PROT_WRITE,MAP_SHARED,fd0,0);
for (i = 0; i < 12; i++)
*ptr++ = 0xaa;
this loop will not write all bytes correctly (every 4 bytes will have 0xaa as
value), here is dump from Lauterbach debugger:
D:83660000|>FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF ................
D:83660010| 000000AA 000000AA 000000AA 0000AA02 ................
and if I use bigger loop
for (i = 0; i < 20; i++)
*ptr++ = 0xaa;
My linux will be crashed on 13 write. So, this is reason why I thought that
byte access is not allowed on mmaped uncached memory.
Is it possible that problem with byte access is related with device mmap
>This stament if of course limited to the CPU's part of the system. Devices
>may have their specific restrictions on access size and its not uncommon to
>have such restrictions though that would seem unlikely for framebuffer
Ok, I understood this.
>If your particular CPU support it you may want to use cache mode "uncached
>accellerated" for a framebuffer. It should deliver significtn performance
>gains yet avoid the need for cache flushes.
Thanks in advance