C/C++ • Re: Allocate memory for DMA on Raspberry Pi 5

Code:

#define PAGE_SIZE (4*1024)void *mapmem(unsigned base, unsigned size){   int mem_fd;   unsigned offset = base % PAGE_SIZE;   base = base - offset;   /* open /dev/mem */   if ((mem_fd = open("/dev/mem", O_RDWR|O_SYNC) ) < 0) {      printf("can't open /dev/mem\nThis program should be run as root\n");      exit (-1);   }   void *mem = mmap(      0,      size,      PROT_READ|PROT_WRITE,      MAP_SHARED,      mem_fd,      base);   printf("base=0x%x, mem=%p\n", base, mem);   if (mem == MAP_FAILED) {      printf("mmap error %d\n", (int)mem);      exit (-1);   }   close(mem_fd);   return (char *)mem + offset;}