BAR (Base Address Register)

/sys/bus/pci/devices/0000:0d:00.0/resource

• Format: start_address end_address flags

sudo dd if=/dev/mem bs=1 count=4 skip=<start_address> 2>/dev/null | hexdump -C

void __iomem *bar_addr;
bar_addr = ioremap(BAR_PHYS_ADDR, BAR_SIZE);
u32 value = readl(bar_addr + 0);

/sys/bus/pci/devices/0000:0d:00.0/resourceN

int fd = open("/sys/bus/pci/devices/0000:0d:00.0/resource2", O_RDWR | O_SYNC);
void *map_base = mmap(0, map_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);