Question

Due to some requirements on speed, we need to some computation in-place on internal memory and then DMA the results of the computation to a external memory. The application runs on a TI DM355 processor which is based on ARM926EJ-S core and a set of TI periferals (EDMA, video accelerators etc).

How cleanly can this be done from the application? Is it as simple as mmap’ing the afore said internal memory address into a virtual space and doing the calculation?

Thanks

Answer 1

You can mmap the /dev/mem device:

int mem_fd = open("/dev/mem", O_RDWR);
void *buffer = mmap(NULL, mem_segment_length, PROT_READ | PROT_WRITE, MAP_SHARED,
                    mem_fd, mem_segment_addr);
close(mem_fd);
/* buffer now points to your device's memory */
/* remember to call msync after writing to this to force changes to write back to
 * /dev/mem */

However, depending on your needs, this may not be sufficient. Another question on here has answers that go more in-depth, but you’re probably better off doing this in a kernel module.