/*
 * dma.c
 * this program demonstrates DMA on the GBA
 */

/* the number of times to transfer the eagle */
#define TIMES 100

/* the width and height of the screen */
#define WIDTH 240
#define HEIGHT 160

/* include the actual image file data */
#include "image.h"

/* the screen is simply a pointer into memory at a specific address this
 *  * pointer points to 16-bit colors of which there are 240x160 */
volatile unsigned short* screen = (volatile unsigned short*) 0x6000000;

/* the display control pointer points to the gba graphics register */
volatile unsigned long* display_control = (volatile unsigned long*) 0x4000000;

/* these identifiers define different bit positions of the display control */
#define MODE3 0x0003
#define BG2 0x0400


/* copy data with a loop */
void memcpy16(unsigned short* dest, unsigned short* source, int amount) {
    for (int i = 0; i < amount; i++) {
        dest[i] = source[i];
    }
}

/* pointer to the DMA source location */
volatile unsigned int* dma_source = (volatile unsigned int*) 0x40000D4;

/* pointer to the DMA destination location */
volatile unsigned int* dma_destination = (volatile unsigned int*) 0x40000D8;

/* pointer to the DMA count/control */
volatile unsigned int* dma_count = (volatile unsigned int*) 0x40000DC;

/* flag for turning on DMA */
#define DMA_ENABLE 0x80000000

/* flags for the sizes to transfer, 16 or 32 bits */
#define DMA_16 0x00000000
#define DMA_32 0x04000000

/* copy data using DMA */
void memcpy16_dma(unsigned short* dest, unsigned short* source, int amount) {
    *dma_source = (unsigned int) source;
    *dma_destination = (unsigned int) dest;
    *dma_count = amount | DMA_16 | DMA_ENABLE;
}

/* the main function */
int main() {
    /* we set the mode to mode 3 with bg2 on */
    *display_control = MODE3 | BG2;

    /* transfer with a loop */
    //for (int t = 0; t < TIMES; t++) {
        //memcpy16((unsigned short*) screen, (unsigned short*) image_data, WIDTH * HEIGHT);
    //}

    /* transfer with DMA */
    for (int t = 0; t < TIMES; t++) {
        memcpy16_dma((unsigned short*) screen, (unsigned short*) image_data, WIDTH * HEIGHT);
    }


    /* set the screen to black, so we know when it's done */
    for (int r = 0; r < HEIGHT; r++) {
        for (int c = 0; c < WIDTH; c++) {
            screen[r * WIDTH + c] = 0;
        }
    }

    /* we now loop forever displaying the image */
    while (1) {
        /* do nothing */
    }
}