#include <stdint.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <unistd.h>

#define GPMC_BASE 0x50000000

#define GPMC_CHIPSELECTCONFIGDISPLACEMENT (0x30 / 4)

#define GPMC_CONFIG1 (0x60 / 4)
#define GPMC_CONFIG2 (0x64 / 4)
#define GPMC_CONFIG3 (0x68 / 4)
#define GPMC_CONFIG4 (0x6c / 4)
#define GPMC_CONFIG5 (0x70 / 4)
#define GPMC_CONFIG6 (0x74 / 4)
#define GPMC_CONFIG7 (0x78 / 4)

static int devmemfd = -1;

//map memory of length "len" at offset "offset"
static void* util_mapmemoryblock(off_t offset, size_t len)
{
	devmemfd = open("/dev/mem", O_RDWR | O_SYNC);
	void* registers = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, devmemfd, offset);
	if (registers == MAP_FAILED) {
		printf("Map failed\n");
	}
	return registers;
}

static void util_unmapmemoryblock(void* block, size_t len)
{
	munmap((void*) block, len);
	if (devmemfd != -1) {
		close(devmemfd);
	}
}

#define REGLEN 0x10000000

static volatile uint32_t* registers = NULL;

static void gpmc_mapregisters()
{
	registers = (uint32_t*) util_mapmemoryblock(GPMC_BASE, REGLEN);
}

static void gpmc_unmapregisters()
{
	util_unmapmemoryblock((void*) registers, REGLEN);
}

static void gpmc_setup(void)
{
	gpmc_mapregisters();

	if (registers != MAP_FAILED) {
		int chipselect = 0;
		int displacement = GPMC_CHIPSELECTCONFIGDISPLACEMENT * chipselect;

		// disable before playing with the registers..
		*(registers + displacement + GPMC_CONFIG7) = 0x00000000;

		*(registers + displacement + GPMC_CONFIG1) = 0x00000000; //No burst, async, 8-bit, non multiplexed
		*(registers + displacement + GPMC_CONFIG2) = 0x00000300; //Assert CS on fclk 0, deassert CS on fclk 3
		*(registers + displacement + GPMC_CONFIG3) = 0x00000000; //Unused ADV/ALE
		*(registers + displacement + GPMC_CONFIG4) = 0x00000301; //Assert OE on fclk 1, deassert OE on fclk 3
		*(registers + displacement + GPMC_CONFIG5) = 0x00020003; //Data valid on fclk 2, cycle time 3 fclks
		*(registers + displacement + GPMC_CONFIG6) = 0x00000000; //No back to back cycle restrictions
		*(registers + displacement + GPMC_CONFIG7) = 0x00000f41; //CS0: Set base address 0x01000000, 16MB region, and enable CS

		gpmc_unmapregisters();
	}
}

static volatile uint8_t* extbus;

void bus_init()
{
	gpmc_setup();

	extbus = (uint8_t*) util_mapmemoryblock(0x01000000, 0x100);
}

void bus_writebyte(uint8_t address, uint8_t data)
{
	*(extbus + address) = data;
}

uint8_t bus_readbyte(uint8_t address)
{
	return *(extbus + address);
}

void bus_shutdown()
{
	util_unmapmemoryblock((void*) extbus, 0x100);
}

int main() {
	bus_init();
	for (int i = 0; i < 10; i++) {
		printf("byte at address %x: %X\n", i, bus_readbyte(i));
	}
	bus_shutdown();
}