Dear all,
I had some problem when I use mmap() file operation in the device driver file
operation. My situation can be described as:
1. I reserve 2MB DDR memory as a look-up-table (LUT) for my customized device.
The physical start address in the memory is 0x03000000 and the size is 2MB.
2. In the device driver, I use mmap file operation to make this memory area
directly accessible by application programs. In the mmap file operation, it
looks like:
if(remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff, vma->vm_end -
vma->vm_start, vma->vm_page_prot)){ return -EAGAIN; }
3. In the application program, I read from a file and initialize the LUT area.
I use the following sentence to mmap the physical address into a virtual one
which could be accessed by the application:
// the physical address is from 0x03000000 with a size of LUT_SIZE_IN_BYTE
equal to 2MB
lut_mem_base = (unsigned int *) mmap(0, LUT_SIZE_IN_BYTE, PROT_READ |
PROT_WRITE, MAP_SHARED, fd, 0x03000000);
Then, I initialize the LUT area with the virtual address specified by
lut_mem_base.
for(i=0;;i++){
fread(&buf, sizeof(unsigned int), 1, fp);
*(lut_mem_base + i) = buf;
if(feop(fp)){
break;
}
}
4. After the initialization of the LUT memory area, in the device driver, DMA
transfer will be enabled using the physical address of 0x03000000 as the source
address. The destination is a register in my customized device. The data is fed
from the memory to my device register.
HOWEVER, I found that the data fed to the device register is not the same as
the one used to initialize the LUT memory. Maybe the DMA fetches wrong data
from different addresses and feeds to my device. Since this is my first time to
use mmap, I am not self-confident to my program, both in the device driver and
in the application. Is there anything wrong with my mmap part? I will
appreciate so much if some experts could give me some hints. Thanks in advance.
BR
Ming
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