Filling the screen with colors in c and assembler (Pasmo, z88dk and sdcc)

The Amstrad CPC has three video modes : "Mode 0" 160×200 pixels with 16 colors, "Mode 1" 320×200 pixels with 4 colors and "Mode 2" 640×200 pixels with 2 colors. The video memory is located between the addresses C000 to FFFF, ie has a size of 3FFF (16,383) bytes. Depending on the mode, each byte represents 2, 4 or 8 pixels of the screen. In this example, we'll just fill the entire screen with the same value 256 times (with values from 0 to 255), so you will see the screen changing color quickly, the program will work in mode 0, to have 16 colors. At the end of this tutorial you can download a zip with all files.

Source code for z88dk:

#include <strings.h>

main()
{
  unsigned char nColor = 0;

  //set mode 0
  #asm
    ld  a,0
    call  $BC0E
  #endasm

  for(nColor = 0; nColor < 255; nColor++)
  {
    memset(0xC000, nColor, 0x3FFF);
  }

  //wait char
  #asm
    call  $BB06
  #endasm
}

Source code for sdcc:

#include <string.h>

void main()
{
  unsigned char nColor = 0;

  //set mode 0
  __asm
    ld  a, #0
    call  #0xBC0E
  __endasm;

  for(nColor = 0; nColor < 255; nColor++)
  {
    memset(0xC000, nColor, 0x3FFF);
  }

  __asm
    call #0xBB06
  __endasm;
}

Source code in assembler:

org #6000
KM_WAIT_CHAR      EQU #BB06

;set mode 0
ld  a, 0
call  #BC0E

;from 0 to 255
ld  d,#00

startloop:
  ld  a, d
  sub #FF
  jr  NC,endloop
  ld  e,d
  push  de

;memset
  ld  hl,#C000
  ld  (hl), e
  ld  e, l
  ld  d, h
  inc de
  ld  bc, #3FFF
  ldir

  pop de
  inc d
  jr  startloop
endloop:

CALL KM_WAIT_CHAR

RET

You should see something like this:

fill

The three binaries have the same speed (as they use to fill ldir), but curiously the binary generated by z88dk occupies 193 bytes, the generated by sdcc occupies 93 bytes and the generated by Pasmo occupies 34 bytes.

You can download a zip with all files here : Filling_the_screen_with_colors_in_c_and_assembler_Pasmo_z88dk_sdcc.zip