Re: [microblaze-uclinux] Relocate sections in bflt file format

[John Williams <jwilliams@xxxxxxxxxxxxxx>]

Hi Tommy,

Tommy Kamps wrote:
> I am running uClinux 2.6.20 on A Xilinx Spartan3E500 Revision D board.
> The MicroBlaze design contains a coprocessor that I have designed myself.
> This coprocessor has an internal block ram and some custom logic and
> is connected to the FSL bus
> and to the PLB for memory access to the block ram.
>
> I have developed a user program that contains two global arrays that
> should be put in the
> block RAM of the coprocessor. When using the Xilinx kernel, this can
> be done by putting the arrays
> in a separate section:
>
> int array_1[16] __attribute__ ((section(".cpmem")));
> int array_2[16] __attribute__ ((section(".cpmem")));
>
> and using a linker script that assigns the PLB address of the
> coprocessor to this section.
>
> Now, I want to run this application in uClinux. The problem is that
> the elf file format is not used here, but the
> Binary Flat File Format (bflt). The linker script that worked for the
> Xilinx MicroBlaze linker does not work for the
> microblaze-uclinux-ld linker. I have found some information about the
> bflt format, but it was not sufficient for me
> to solve this problem. I know I have to do something with relocation,
> but I am not sure how, and I could not find sufficient
> information about this subject.
>
> Can someone please give some pointers to fix this?

There's no clean way to do this - under Linux you are not allowed to 
pin userspace data or code to fixed physical addresses.

That said, you can hack it up by just forcing userspace pointers to 
known, fixed addresses:

#define BRAM_ADDRESS 0x2000

struct my_struct {

   };

struct my_struct *bram_array = (struct my_struct *)BRAM_ADDRESS;

You can then dereference the mbra_array ptr and it will be resident in BRAM.

Of course, this will completely break if you run two instances of your 
program, and you are on your own when it comes to guaranteeing mutex on 
the data etc.

If you want to go further you could write your own userspace memory 
allocator routines, call them bram_malloc(), bram_free() etc, if you 
need that sort of flexibility.

Another, slightly cleaner way to do it, might be to use mmap(), like this:

int fd;
int *p;
fd = open("/dev/mem", O_RDWR);
p = (int *)mmap(0, 256, PROT_READ|PROT_WRITE,
        MAP_PRIVATE, fd, BRAM_ADDRESS);
if (p == MAP_FAILED) {
        printf("Err: cannot access adder!\n");
        return -1;
}

This achieves the same effect, but if you ever port your design to 
PowerPC or MicroBlaze with MMU, it will still work!

Regards,

John

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