vdp: print hex to the screen

vdp.s

@@ -2,9 +2,27 @@
 VDP_VRAM = $4000
 VDP_REG  = $4001
 
+VDP_WRITE_VRAM_BIT = $40
 VDP_REGISTER_BITS = $80
 
+VDP_NAME_TABLE_BASE = $0000
+VDP_PATTERN_TABLE_BASE = $0800
+
+  .macro vdp_write_vram
+  lda #<(\1)
+  sta VDP_REG
+  lda #(VDP_WRITE_VRAM_BIT | >\1)
+  sta VDP_REG
+  .endm
+
 vdp_reset:
+  jsr vdp_reg_reset
+  jsr vdp_initialize_pattern_table
+  jsr vdp_initialize_name_table
+  jsr vdp_enable_display
+  rts
+
+vdp_reg_reset:
   pha
   phx
 
@@ -20,11 +38,51 @@ vdp_reg_reset_loop:
   inx
   cpx #(vdp_end_register_inits - vdp_register_inits)
   bne vdp_reg_reset_loop
+  plx
+  pla
+  rts
 
+vdp_initialize_pattern_table:
+  ; initialize the pattern table to the 16 hex digits
+  pha
+  phx
+  vdp_write_vram VDP_PATTERN_TABLE_BASE
+  ldx #0
+vdp_pattern_table_loop:
+  lda vdp_hex_digits,x
+  sta VDP_VRAM
+  inx
+  cpx #(vdp_end_hex_digits - vdp_hex_digits)
+  bne vdp_pattern_table_loop
   plx
   pla
   rts
 
+vdp_initialize_name_table:
+  ; initialize to "0123456789ABCDEF"
+  pha
+  phx
+  vdp_write_vram VDP_NAME_TABLE_BASE
+  lda #0
+vdp_name_table_loop:
+  sta VDP_VRAM
+  ina
+  cmp #$10
+  bne vdp_name_table_loop
+  plx
+  pla
+  rts
+
+vdp_enable_display:
+  pha
+  lda vdp_register_1
+  ora #%01000000 ; enable the active display
+  sta VDP_REG
+  lda #(VDP_REGISTER_BITS | 1)
+  sta VDP_REG
+  pla
+  rts
+
 vdp_register_inits:
 vdp_register_0: .byte %00000000 ; 0  0  0  0  0  0  M3 EXTVDP
 vdp_register_1: .byte %10010000 ;16k Bl IE M1 M2 0 Siz MAG
@@ -36,3 +94,21 @@ vdp_register_6: .byte $00       ; Sprite pattern generator (currently unused)
 vdp_register_7: .byte $B4       ; FG/BG. 4=>Dark blue, B=>Light yellow
 vdp_end_register_inits:
 
+vdp_hex_digits:
+  .byte $70,$88,$98,$A8,$C8,$88,$70,$00 ; 0
+  .byte $20,$60,$20,$20,$20,$20,$70,$00 ; 1
+  .byte $70,$88,$08,$30,$40,$80,$F8,$00 ; 2
+  .byte $F8,$08,$10,$30,$08,$88,$70,$00 ; 3
+  .byte $10,$30,$50,$90,$F8,$10,$10,$00 ; 4
+  .byte $F8,$80,$F0,$08,$08,$88,$70,$00 ; 5
+  .byte $38,$40,$80,$F0,$88,$88,$70,$00 ; 6
+  .byte $F8,$08,$10,$20,$40,$40,$40,$00 ; 7
+  .byte $70,$88,$88,$70,$88,$88,$70,$00 ; 8
+  .byte $70,$88,$88,$78,$08,$10,$E0,$00 ; 9
+  .byte $20,$50,$88,$88,$F8,$88,$88,$00 ; A
+  .byte $F0,$88,$88,$F0,$88,$88,$F0,$00 ; B
+  .byte $70,$88,$80,$80,$80,$88,$70,$00 ; C
+  .byte $F0,$88,$88,$88,$88,$88,$F0,$00 ; D
+  .byte $F8,$80,$80,$F0,$80,$80,$F8,$00 ; E
+  .byte $F8,$80,$80,$F0,$80,$80,$80,$00 ; F
+vdp_end_hex_digits: