Hi
I too am working on the timer4 and trying to access the registers using
dev/mem. However I get bus error when trying to read the address. Can you
let me know how you did this using dev/mem.
My code is posted below:
#include <unistd.h>#include <fcntl.h>#include <sys/mman.h>#include
<stdio.h>#include<stdlib.h>#include<string.h>#include <signal.h>
#define TIMER4_START_addr 0x48044000#define TIDR 0x00#define TIOCP_CFG 0x10
int main(){
unsigned int reg;
char *timer_addr = NULL;
printf("\n Start Pgm");
int mem, integer;
if ((mem = open ("/dev/mem", O_RDWR | O_SYNC)) < 0)
{
printf("Cannot open /dev/mem\n");
return 1;
}
printf("Opened /dev/mem\n");
timer_addr = mmap(0, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, mem,
TIMER4_START_addr);
printf("GPIO mapped to %p\n", timer_addr);
reg = *((int*) timer_addr);
printf("GPIO1 configuration: %x\n", reg);
return 0;}
Regards
Anand
On Wednesday, 14 May 2014 00:26:47 UTC+5:30, [email protected] wrote:
>
> Hi,
>
> I am using TI AM335x BeagleBone. My aim is to get fast and reliable time
> values from user-space using dmtimer.
>
> When I I read (and print) tick values of DMTimer2 though /dev/mem, I have
> the following:
>
> 2703519715
> 2703525474
> 2703527633
> 2703529333
> 2703530952
> 2703532576
> 2703538448
> 2703541914
> 2703543656
> 2703545281
> 2703546900
>
> However, when I invoke device driver with mmap operation and then in user
> space interact with this device, I have a strange behaviour.
> Ticks are repeated periodically:
>
> 1287902680
> 1287911282
> 1287911282
> 1287911282
> 1287911282
> 1287911282
> 1287925948
> 1287925948
> 1287925948
> 1287935869
> 1287935869
> 1287935869
> 1287944825
> 1287944825
> 1287950109
> 1287950109
> 1287959332
>
> I am not sure, but it looks like L1/L2 caches are overflowed. My question is
> what can cause this behaviour. And if it is CPU caches, how they can be
> cleared.
> I found this answer
> http://stackoverflow.com/questions/3446138/how-to-clear-cpu-l1-and-l2-cache,
> but I doubt how I can apply this method.
> Do you have any suggestions? I will appreciate any help.
>
>
> If it is necessary, I post here briefly the way how I obtaine these ticks vs
> driver.
>
> 1. remapping of a specific region in kernel space (0x48040000 - DMTIMER2
> register start address):
>
> static int simple_remap_mmap(struct file *filp, struct vm_area_struct *vma)
> {
> unsigned long off = vma->vm_pgoff << PAGE_SHIFT;
> // generate the correct page frame number
> unsigned long pfn = (0x48040000 + off) >> PAGE_SHIFT;
> // vsize is the requested size of virtual memory
> unsigned long vsize = vma->vm_end - vma->vm_start;
> // psize is the physical I/O size that is left after the offset has been
> specified
> unsigned long psize = 0x48040000 + 32 - off;
> // refuses to map addresses that extend beyond the allowed memory range
> if (vsize > psize)
> {
> return -EINVAL;
> }
> if (remap_pfn_range(vma, vma->vm_start, pfn, vsize, vma->vm_page_prot))
> {
> return
> -EAGAIN;
> }
> vma->vm_ops = &simple_remap_vm_ops;
> simple_vma_open(vma);
> return 0;
> }
>
> 2. in user space I do it approximately in the following way:
>
> volatile unsigned char* dmt2_regs;
> dmt2_regs = (unsigned char*) mmap(NULL, 0x1000, PROT_READ|PROT_WRITE,
> MAP_SHARED, fd, 0);
> while (true)
> {
> uint32_t t0 = * (uint32_t*) ( dmt2_regs + 0x3c );
> std::cout << t0 << std::endl;
> }
>
>
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