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; } -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
