Code finalization for bouncing sprite.

const.h

@@ -1,8 +1,15 @@
 #pragma once
 
-#define VERTICAL_OFFSET 30
+#define FRAME_PIXEL_WIDTH 1024 // [system clock]
-#define HORIZONTAL_OFFSET 168
+#define FRAME_PIXEL_HEIGHT 256 // [line]
-#define LINE_BUFFER_SIZE 160
 
-#define BLACK 0x00
+#define BACK_PORCH_OFFSET 100 // [system clock]
-#define WHITE 0xff
+#define FRONT_PORCH_OFFSET 40 // [system clock]
+
+#define SPRITE_WIDTH 80  // [system clock]
+#define SPRITE_HEIGHT 64 // [line]
+
+// Time spent from the horizontal sync pulse,
+// to the first displayed dot.
+// This is given as HSYNC_INT_TUNE + HSYNC_TIMER_TUNE + C part
+#define HSYNC_TUNE 70

main.S

@@ -38,67 +38,76 @@ main_asm:
 
 .global int_horizontal_sync_s
 int_horizontal_sync_s:
-    push r31
+    push r31            ; +2
-    push r30
+    push r30            ; +2
 
     ; load timer to trigger isr at the beginning of the visible scanline
     ; reset counter to 0
-    ldi r31, 0
+    ldi r31, 0          ; +1
-    sts TCNT1H, r31
+    sts TCNT1H, r31     ; +2
-    sts TCNT1L, r31
+    sts TCNT1L, r31     ; +2
 
     ; set counter TOP (MSB first!)
-    lds r31, hpos + 1
+    lds r31, hpos + 1   ; +2
-    lds r30, hpos
+    lds r30, hpos       ; +2
-    sts OCR1AH, r31
+    sts OCR1AH, r31     ; +2
-    sts OCR1AL, r30
+    sts OCR1AL, r30     ; +2
 
     ; clear any pending interrupt
-    ldi r31, 0x7
+    ldi r31, 0x7        ; +1
-    sts TIFR1, r31
+    sts TIFR1, r31      ; +2
 
     ; enable interrupt timer A
-    lds r31, TIMSK1
+    lds r31, TIMSK1     ; +2
-    ori r31, 0x02
+    ori r31, 0x02       ; +1
-    sts TIMSK1, r31
+    sts TIMSK1, r31     ; +2
+
+                        ; total: 25
+                        ; HSYNC_INT_TUNE = 25
+                        ; this adds up for HSYNC_TUNE
 
     pop r30
     pop r31
     ret
 
-.global int_timer_0
+.global int_timer_1
-int_timer_0:
+int_timer_1:
     ; here we are at the beginning of the visible line
-    push r31
+    ; jmp (from C)      ; +3
-    in r31, IO(SREG)
+    push r31            ; +2
-    push r31
+    in r31, IO(SREG)    ; +1
-    push r30
+    push r31            ; +2
-    push r29
+    push r30            ; +2
-    push r25
+    push r29            ; +2
+    push r25            ; +2
 
     ; turn off interrupt
-    lds r31, TIMSK1
+    lds r31, TIMSK1     ; +2
-    andi r31, 0xfd      ; mask disable interrupt timer A
+    andi r31, 0xfd      ; mask disable interrupt timer A, +1
-    sts TIMSK1, r31
+    sts TIMSK1, r31     ; +2
 
-    lds r31, show_image
+    lds r31, show_image ; +2
-    cpi r31, 0x1
+    cpi r31, 0x1        ; +1
-    brne jump_table_return_address
+    brne jump_table_return_address  ; +1 (not taken)
 
-    lds zl, current_jump_table
+    lds zl, current_jump_table      ; +2
-    lds zh, current_jump_table + 1
+    lds zh, current_jump_table + 1  ; +2
 
-    clr r0
+    clr r0              ; +1
-    lds r29, line
+    lds r29, line       ; +2
-    lds r25, vpos
+    lds r25, vpos       ; +2
-    sub r29, r25
+    sub r29, r25        ; +1
 
-    add zl, r29
+    add zl, r29         ; +1
-    adc zh, r0
+    adc zh, r0          ; +1
-    add zl, r29
+    add zl, r29         ; +1
-    adc zh, r0
+    adc zh, r0          ; +1
 
-    ijmp
+    ijmp                ; +2
+
+                        ; total: 39
+                        ; HSYNC_TIMER_TUNE = 39
+                        ; this adds up for HSYNC_TUNE
 
 .global jump_table_return_address
 jump_table_return_address:

main.c

@@ -18,35 +18,46 @@ volatile uint16_t frame = 0;
 volatile uint16_t line = 0xfe;
 volatile uint8_t image = 0xff;
 
-// horizontal and vertical position of bouncing logo
+// horizontal and vertical position
+// (and current increments)
+// of bouncing sprite
 volatile uint8_t vpos = 0;
 volatile uint16_t hpos = 0;
 volatile int8_t vinc = +1;
 volatile int8_t hinc = +1;
 
+// vertical sync interrupt
 void int_vertical_sync_s(void);
 ISR(INT0_vect) {
+  // count frames
   frame += 1;
+
+  // move sprite
   vpos += vinc;
   hpos += hinc;
 
+  // invert bouncing direction
   if (vpos == 0)
     vinc = +1;
-  if (vpos == 256 - 64)
+  if (vpos == FRAME_PIXEL_HEIGHT - SPRITE_HEIGHT)
     vinc = -1;
-  if (hpos == HORIZONTAL_OFFSET)
+  if (hpos == BACK_PORCH_OFFSET)
     hinc = +1;
-  if (hpos == 1024 - 80)
+  if (hpos ==
+      FRAME_PIXEL_WIDTH - SPRITE_WIDTH - FRONT_PORCH_OFFSET - HSYNC_TUNE)
     hinc = -1;
 
   int_vertical_sync_s();
 }
 
+// horizontal sync interrupt
 void int_horizontal_sync_s(void);
 ISR(INT1_vect) {
+  // count lines
   line += 1;
-  // if (line >= 256)
+
-  if (line >= vpos + 64)
+  // we are past the last line of the sprite
+  if (line >= vpos + SPRITE_HEIGHT)
     return;
 
   if (line >= vpos)
@@ -54,8 +65,8 @@ ISR(INT1_vect) {
 }
 
 ISR(TIMER1_COMPA_vect, ISR_NAKED) {
-  // back porch timer interrupt
+  // end-of back porch timer interrupt
-  asm("jmp int_timer_0");
+  asm("jmp int_timer_1");
 }
 
 // external assembly main loop
@@ -76,10 +87,5 @@ int main() {
   TCCR1A = 0x00; // don't connect output pins to timer, CTC[1:0] mode
   TCCR1B = 0x09; // CTC[3:2] mode, no prescaler
 
-#if 0
-  TCCR0A = 0x02; // don't connect output pins to timer, CTC[1:0] mode
-  TCCR0B = 0x01; // CTC[2] mode, no prescaler
-#endif
-
   main_asm();
 }

samples/bouncing-logo.pbm

@@ -1,23 +1,6 @@
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