fb.c

#include "mailbox.h"
#include "fb.h"
#include "printf.h"

// This prevents the GPU and CPU from caching mailbox messages
#define GPU_NOCACHE 0x40000000

typedef struct {
  unsigned int width;       // width of the display
  unsigned int height;      // height of the display
  unsigned int virtual_width;  // width of the virtual framebuffer
  unsigned int virtual_height; // height of the virtual framebuffer
  unsigned int pitch;       // number of bytes per row
  unsigned int depth;       // number of bits per pixel
  unsigned int x_offset;    // x of the upper left corner of the virtual fb
  unsigned int y_offset;    // y of the upper left corner of the virtual fb
  unsigned int framebuffer; // pointer to the start of the framebuffer
  unsigned int size;        // number of bytes in the framebuffer
} fb_config_t;

// Why is fb volatile?
// Why is it aligned to a multiple of 16?
volatile fb_config_t fb __attribute__ ((aligned(16)));

void fb_init(unsigned width, unsigned height, unsigned depth)
{
  fb.width = width;
  fb.virtual_width = width;
  fb.height = height;
  fb.virtual_height = height;
  fb.depth = depth * 8; // convert number of bytes to number of bits
  fb.x_offset = 0;
  fb.y_offset = 0;

  // the manual requires we to set these value to 0
  // the GPU will return new values
  fb.pitch = 0;
  fb.framebuffer = 0;
  fb.size = 0;

  // Send the fb struct to the GPU
  // Why do we add in GPU_NOCACHE?
  mailbox_write(MAILBOX_FRAMEBUFFER, (unsigned)&fb + GPU_NOCACHE);
  (void) mailbox_read(MAILBOX_FRAMEBUFFER);

  printf("width = %d\n", fb.width );
  printf("height = %d\n", fb.height );
  printf("virtual width = %d\n", fb.virtual_width );
  printf("virtual height = %d\n", fb.virtual_height );
  printf("depth = %d\n", fb.depth );
  printf("size = %d\n", fb.size );
  printf("pitch = %d\n", fb.pitch );
  printf("buffer = %08x\n", fb.framebuffer );
}