Add bouncing sprite. First experiment.

const.h

@@ -1,7 +1,7 @@
 #pragma once
 
 #define VERTICAL_OFFSET 30
-#define HORIZONTAL_OFFSET 192
+#define HORIZONTAL_OFFSET 168
 #define LINE_BUFFER_SIZE 160
 
 #define BLACK 0x00

main.S

@@ -36,29 +36,14 @@ main_asm:
 1:
     rjmp 1b
 
-.global int_horizontal_sync
+.global int_horizontal_sync_s
-int_horizontal_sync:    ; +3
+int_horizontal_sync_s:
-    push r31            ; +5
+    push r31
-    in r31, IO(SREG)    ; +6, status register
-    push r31            ; +8
-    push r30            ; +10
 
-    ; if (0 <= line < 256), then enter
+    ; load timer to trigger isr at the beginning of the visible scanline
-    lds r30, line       ; +12
-    lds r31, line + 1   ; +14
-    adiw z, 1           ; +16
-    sts line, r30       ; +18
-    sts line + 1, r31   ; +20
-    cpi r31, 0          ; +21
-    breq enter          ; +23
-    jmp int_horizontal_sync_end
-
-enter:
-    ; here, +23 cycles have passed since horizontal sync
-    ; so, there are still ~168 cycles before first useful data
     ldi r31, 0
     sts TCNT0, r31
-    ldi r31, HORIZONTAL_OFFSET  ; set counter TOP
+    lds r31, hpos       ; set counter TOP
     sts OCR0A, r31
 
     ldi r31, 0x7        ; clear any pending interrupt
@@ -68,12 +53,8 @@ enter:
     ori r31, 0x02       ; mask enable interrupt timer A
     sts TIMSK0, r31
 
-int_horizontal_sync_end:
-    pop r30
     pop r31
-    out IO(SREG), r31
+    ret
-    pop r31
-    reti
 
 .global int_timer_0
 int_timer_0:
@@ -83,6 +64,7 @@ int_timer_0:
     push r31
     push r30
     push r29
+    push r25
 
     ; turn off interrupt
     lds r31, TIMSK0
@@ -96,11 +78,11 @@ int_timer_0:
     lds zl, current_jump_table
     lds zh, current_jump_table + 1
 
-;    ldi zl, pm_lo8(line_jump_table_0)
-;    ldi zh, pm_hi8(line_jump_table_0)
-
     clr r0
     lds r29, line
+    lds r25, vpos
+    sub r29, r25
+
     add zl, r29
     adc zh, r0
     add zl, r29
@@ -110,6 +92,7 @@ int_timer_0:
 
 .global jump_table_return_address
 jump_table_return_address:
+    pop r25
     pop r29
     pop r30
     pop r31
@@ -117,8 +100,8 @@ jump_table_return_address:
     pop r31
     reti
 
-.global int_vertical_sync
+.global int_vertical_sync_s
-int_vertical_sync:
+int_vertical_sync_s:
     push r31
     in r31, IO(SREG)
     push zl
@@ -126,12 +109,6 @@ int_vertical_sync:
     push yl
     push yh
 
-    lds r31, frame + 1
-    lds r30, frame
-    adiw z, 1
-    sts frame + 1, r31
-    sts frame, r30
-
     ldi r30, 1
     ldi r31, 0
     sts line, r30

main.c

@@ -18,14 +18,41 @@ volatile uint16_t frame = 0;
 volatile uint16_t line = 0xfe;
 volatile uint8_t image = 0xff;
 
-ISR(INT0_vect, ISR_NAKED) {
+// horizontal and vertical position of bouncing logo
-  // vertical sync interrupt
+volatile uint8_t vpos = 0;
-  asm("jmp int_vertical_sync");
+volatile uint8_t hpos = 0;
+volatile int8_t vinc = +1;
+volatile int8_t hinc = +1;
+
+void int_vertical_sync_s(void);
+ISR(INT0_vect) {
+  frame += 1;
+  vpos += vinc;
+  hpos += hinc;
+
+  if (vpos == 0)
+    vinc = +1;
+  if (vpos == 256 - 64)
+    vinc = -1;
+  if (hpos == HORIZONTAL_OFFSET)
+    hinc = +1;
+  if (hpos == 255 - 40)
+    hinc = -1;
+
+  int_vertical_sync_s();
 }
-ISR(INT1_vect, ISR_NAKED) {
+
-  // horizontal sync interrupt
+void int_horizontal_sync_s(void);
-  asm("jmp int_horizontal_sync");
+ISR(INT1_vect) {
+  line += 1;
+  // if (line >= 256)
+  if (line >= vpos + 64)
+    return;
+
+  if (line >= vpos)
+    int_horizontal_sync_s();
 }
+
 ISR(TIMER0_COMPA_vect, ISR_NAKED) {
   // back porch timer interrupt
   asm("jmp int_timer_0");

samples/bouncing-logo.pbm

@@ -0,0 +1,40 @@
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