Lab2: Splash

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在啟動時，透過mailbox設定GPU framebuffer顯示splash image。

Setup

參考官方文件及範例。

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void fb_init() {
  mbox[0] = 35 * 4;
  mbox[1] = MBOX_REQUEST;

  /* Set physical width/height */
  mbox[2] = MBOX_TAG_SET_PHY_WH;
  mbox[3] = 8;
  mbox[4] = MBOX_TAG_REQ;
  mbox[5] = 1024; // width
  mbox[6] = 768;  // height

  /* Set virtual width/height */
  mbox[7] = MBOX_TAG_SET_VIR_WH;
  mbox[8] = 8;
  mbox[9] = MBOX_TAG_REQ;
  mbox[10] = 1024; // virtual width
  mbox[11] = 768;  // virtual height

  /* Set virtual offset */
  mbox[12] = MBOX_TAG_SET_VIR_OFFSET;
  mbox[13] = 8;
  mbox[14] = MBOX_TAG_REQ;
  mbox[15] = 0; // X offset
  mbox[16] = 0; // Y offset

  /* Set depth */
  mbox[17] = MBOX_TAG_SET_DEPTH;
  mbox[18] = 4;
  mbox[19] = MBOX_TAG_REQ;
  mbox[20] = 32; // bits per pixel

  /* Set pixel order */
  mbox[21] = MBOX_TAG_SET_PIXEL_ORDER;
  mbox[22] = 4;
  mbox[23] = MBOX_TAG_REQ;
  mbox[24] = 1; // 0x0: BGR, 0x1: RGB

  /* Allocate framebuffer */
  mbox[25] = MBOX_TAG_ALLOCATE_BUFFER;
  mbox[26] = 8;
  mbox[27] = MBOX_TAG_REQ;
  mbox[28] = 4096; // 1. alignment (req) 2. frame buffer base address (res)
  mbox[29] = 0;    // frame buffer size (res)

  /* Get pitch */
  mbox[30] = MBOX_TAG_GET_PITCH;
  mbox[31] = 4;
  mbox[32] = MBOX_TAG_REQ;
  mbox[33] = 0; // res: bytes per line

  mbox[34] = MBOX_TAG_LAST;

  // this might not return exactly what we asked for, could be
  // the closest supported resolution instead
  if (mbox_call(MBOX_CH_PROP) && mbox[20] == 32 && mbox[28] != 0) {
    mbox[28] &= 0x3FFFFFFF; // convert GPU address to ARM address
    width = mbox[5];        // get actual physical width
    height = mbox[6];       // get actual physical height
    pitch = mbox[33];       // get number of bytes per line
    isrgb = mbox[24];       // get the actual channel order
    fb = (void *)((unsigned long)mbox[28]);
  } else {
    uart_printf("Unable to set screen resolution to 1024x768x32\n");
  }
}

Show splash image

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void fb_showpicture() {
  /* Safety check */
  if (!fb)
    return;

#define WHITE 0xFFFFFFFF
#define BLACK 0x0
#define BLOCK_SIZE 1 << 6 // 64x64 pixel
  unsigned int x_count = 0, y_count = 0, acc = 0;
  for (void *y = fb; y < fb + height * pitch; y += pitch, ++y_count) {
    if (y_count & BLOCK_SIZE) {
      y_count = 0;
      acc++;
    }
    for (unsigned int *xy = (unsigned int *)y;
         xy < (unsigned int *)y + (pitch >> 2); xy += 1, ++x_count) {
      if (x_count & BLOCK_SIZE) {
        x_count = 0;
        acc++;
      }
      *xy = acc & 1 ? WHITE : BLACK;
    }
  }

#undef BLOCK_SIZE
#undef WHITE
#undef BLACK
}

由於會用到UART顯示錯誤訊息，因此UART初始化必須優先於fb_init()。

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void main() {
  uart_init(115200);
  uart_flush();
  fb_init();
  fb_showpicture();