Add graphics mode selector

1 files changed, 46 insertions, 23 deletions

diff --git a/asm/bootstrap.atk16 b/asm/bootstrap.atk16
index 813ebb5..2aa5d88 100644
--- a/asm/bootstrap.atk16
+++ b/asm/bootstrap.atk16
@@ -1,42 +1,65 @@
-@let stack_segment 0x8000
-@let vector_table  0x10
-@let mmio_segment  0xE000
-@let terminal_addr 0xE000
-@let keyboard_addr 0xE001
-@let sprite_mem    0xE800
+; vector table fields
+@let vector_table    0x10
+@let vt_ISRO         0x10 ; ISR0
+@let vt_ISR1         0x11 ; ISR1
+@let vt_ISR2         0x12 ; ISR2
+@let vt_ISR3         0x13 ; ISR3
+@let vt_stack_addr   0x14 ; Stack address
+@let vt_term_pp_addr 0x15 ; Terminal peripheral address
+@let vt_kb_pp_addr   0x16 ; Keyboard peripheral address
+@let vt_gr_mode_addr 0x17 ; Graphics mode setting address
+
+; memory segments
+@let stack_segment   0x8000
+@let mmio_segment    0xE000
+@let terminal_addr   0xE000
+@let keyboard_addr   0xE001
+@let gr_mode_addr    0xE002
+@let sprite_mem      0xE800
+
+; graphics mode settings
+@let gr_disabled_mode 0b00
+@let gr_text_mode     0b01
+@let gr_sprite_mode   0b10
 
 @address vector_table
-  keyboard_isr   ; 0x10 ISR0
-  hlt_isr        ; 0x11 ISR1
-  hlt_isr        ; 0x12 ISR2
-  hlt_isr        ; 0x13 ISR3
-  stack_segment  ; 0x14 Stack address
-  0x0            ; 0x15 <unused>
-  terminal_addr  ; 0x16 Terminal peripheral address
-  keyboard_addr  ; 0x17 Keyboard peripheral address
+  keyboard_isr   ; 0x10
+  hlt_isr        ; 0x11
+  hlt_isr        ; 0x12
+  hlt_isr        ; 0x13
+  stack_segment  ; 0x14
+  terminal_addr  ; 0x15
+  keyboard_addr  ; 0x16
+  gr_mode_addr   ; 0x17
 
 @label hlt_isr
   ldi 0x55 RE
   hlt
 
 @label keyboard_isr
-  spu RA         ; use RA, RB
+  spu RA                  ; use RA, RB
   spu RB
-  ldi 0x17 RA    ; RA := 0x17 Keyboard peripheral address pointer
-  ldr RA RA      ; RA := 0xE001 Keyboard peripheral address deref
-  ldr RA RA      ; RA := <16-bit keyboard character code> from MMIO register
-  ldi 0x16 RB    ; RB := 0x16 Terminal peripheral address pointer
-  ldr RB RB      ; RB := 0xE000 Terminal peripheral address deref
-  str RA RB      ; terminal <- character code
-  spo RB         ; restore RA, RB
+  ldi vt_kb_pp_addr RA    ; RA := 0x17 Keyboard peripheral address pointer
+  ldr RA RA               ; RA := 0xE001 Keyboard peripheral address deref
+  ldr RA RA               ; RA := <16-bit keyboard character code> from MMIO register
+  ldi vt_term_pp_addr RB  ; RB := 0x16 Terminal peripheral address pointer
+  ldr RB RB               ; RB := 0xE000 Terminal peripheral address deref
+  str RA RB               ; terminal <- character code
+  spo RB                  ; restore RA, RB
   spo RA
   rti
 @label program_segment
 
 @address 0x0
 ; set up stack pointer to point to beginning of stack segment
-  ldi 0x14 RA
+  ldi vt_stack_addr RA
   ldr RA RF
+; set graphics mode to disabled
+  ldi vt_gr_mode_addr RA
+  ldr RA RA
+  ldi gr_disabled_mode RB
+  str RB RA
+; jump to main (user defined)
   jpi main
 
 @address program_segment