access registers

[Aurele]

hi all

I am new on this forum and new on linux (and french for 23 years).
I will try to write correctly but be indulgent...
so as describe in the title I have a CPU ARM and I want to access a register.
i tried with mmap but it doesn't work.
i attach my program if someone see the problem...
so when I run the program there isn't any error, all works (open, mmap ...) but I know that my program do nothing because i have ask to read something that i know and there is nothing...

so please help me
thanks

[Rubberman]

There are several problems with this code.

1. The data type for your base address which you are going to map is off_t not the unsigned int you use for the variable registre. Second, the value passed to mmap for the hardware address MUST be a multiple of the page size. You think you are doing with by the expression (registre & 0xFFFFF000, but there is no guarantee of that. What I usually do is pass in a base address and an offset from the address to the register in question. Than after mapping the base address to a virtual (mapped) address, I simply add the offset of the register to the virtual address (map_base).

In reality, your registre & 0xFFFFF000 should work ok. I do wonder why you are executing msync(). This is not a memory-mapped physical file, so it is possible that this is causing a problem with reading the register. Another possibility is that you haven't enabled the device that the register is associated with. I know that on ARM boards I use, there is the need to do an 8-bit I/O out operation on a specific address to enable a PC-104 daughter board, for instance.