# Re: Problem trying to address custom hardware

- From: Matt Porter \<mporter@kernel.crashing.org\>
- Date: 2004-08-25 17:40:59 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2004/08/9394802
- Thread: https://ratatoskr.run/linuxppc-dev/2004/08/9394802/t.md

```text

[your mailer is really bad and should be fixed, this required heavy editing]

On Tue, Aug 24, 2004 at 04:10:15PM -0700, Oliver King-Smith wrote:
> memfd = open("/dev/mem", O_RDWR);
> if (memfd){
>  pCPLD = (CPLD_REGISTERS *) mmap(0,
>  CPLD_SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE,
>  memfd, CPLD_OFFSET);

Others addressed your core problem, but you should know that this
mmap request won't produce the desired result. You need MAP_SHARED
since MAP_PRIVATE will result in a COW when you attempt to modify
your register.

-Matt

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
```