code:

void BLIT_16x16_font_glyph(uint8_t *destination, uint8_t x, uint8_t y, uint8_t *source, uint8_t c)
{
  //Blit a glyph from an 16x16 font sheet.
  //A sheet is 256x256px = 16x16 glyphs.

  uint16_t source_x = (c * 16) % 256;
  uint16_t source_y = (c & 0xF0) + 128;
  
  MMIO32(A1_BASE)   = (long)destination;	//pixel buffer to write to
  MMIO32(A1_PIXEL)  = BLIT_XY(x, y);		//pixel offset to write to
  MMIO32(A1_FPIXEL) = 0;
  MMIO32(A1_FLAGS)  = PITCH1 | PIXEL1 | WID320 | XADDPIX | YADD0;	//contiguous pixels, 1bpp, 320px wide pixel buffer, increment by 1 pixel per inner loop
  MMIO32(A1_STEP)   = BLIT_XY(320-16, 0);	//after drawing 16 pixels, advance the pointer to the next scanline of the pixel buffer
  
  MMIO32(A2_BASE)   = (long)source;		//bitmap we're reading from
  MMIO32(A2_PIXEL)  = BLIT_XY(source_x, source_y);	//pixel location of (0,0) in the character
  MMIO32(A2_STEP)   = BLIT_XY(256-16, 0);	//after drawing 16 pixels, advance the pointer to the next scanline of the character
  MMIO32(A2_FLAGS)  = PITCH1 | PIXEL1 | WID256 | XADDPIX | YADD0;	//contiguous pixels, 1bpp, 256px wide bitmap, increment by 1 pixel per inner loop
  
  MMIO32(B_COUNT)   = BLIT_XY(16, 16);	//blit 16x16 pixels

  //SRCEN and DSTEN must be enabled for blits below 8bpp
  MMIO32(B_CMD)     = SRCEN | DSTEN | UPDA1 | UPDA2 | LFU_REPLACE; //read from the source and destination, enable A1_STEP and A2_STEP, destination = source
}