an hardcoded demo

prints "RE", a vertical line, and a counter

const.h

@@ -2,3 +2,7 @@
 
 #define VERTICAL_OFFSET 30
 #define HORIZONTAL_OFFSET 192
+#define LINE_BUFFER_SIZE 160
+
+#define BLACK 0x00
+#define WHITE 0xff

main.S

@@ -2,14 +2,6 @@
 #include "macro.h"
 #include "const.h"
 
-.data
-
-frame:
-.word 0
-
-line:
-.word 0
-
 .text
 
 .global main
@@ -43,9 +35,12 @@ main:
     ldi r16, 1
     sts line, r16
 
+    call setup_c
+
     sei                 ; global interrupt enable
 
 1:
+    call loop_c
     rjmp 1b
 
 .global int_horizontal_sync
@@ -94,6 +89,8 @@ int_timer_0:
     push r31
     in r31, IO(SREG)
     push r31
+    push r30
+    push r29
 
     ; turn off interrupt
     lds r31, TIMSK0
@@ -101,28 +98,17 @@ int_timer_0:
     sts TIMSK0, r31
 
     ; draw things
-    lds r31, frame
-    andi r31, 0x70
-    cpi r31, 0
-    breq 2f
-1:
-    dec r31
-    brne 1b
-2:
+    ldi r30, lo8(line_buffer)
+    ldi r31, hi8(line_buffer)
 
-    sbi IO(PORTB), 4
+.rept LINE_BUFFER_SIZE
+    ld r29, z+
+    out IO(PORTB), r29
     nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    nop
-    cbi IO(PORTB), 4
+.endr
 
+    pop r29
+    pop r30
     pop r31
     out IO(SREG), r31
     pop r31

main.c

@@ -1,5 +1,11 @@
 #include <avr/io.h>
 #include <avr/interrupt.h>
+#include "const.h"
+#include <string.h>
+
+volatile uint16_t frame;
+volatile uint16_t line;
+volatile char line_buffer[LINE_BUFFER_SIZE];
 
 ISR(INT0_vect, ISR_NAKED) {
     asm("jmp int_vertical_sync");
@@ -10,3 +16,40 @@ ISR(INT1_vect, ISR_NAKED) {
 ISR(TIMER0_COMPA_vect, ISR_NAKED) {
     asm("jmp int_timer_0");
 }
+
+void setup_c() {
+    /*
+    for (int i = 0; i < LINE_BUFFER_SIZE; ++i) {
+        line_buffer[i] = (i % 2) ? 0x0 : 0xff;
+    }
+    */
+}
+
+void loop_c() {
+    for (;;) {
+        const int current_line = line;
+        switch (current_line) {
+            case 76: case 134: memcpy(line_buffer, "AAAAAAAAAAAAAAAAAAAAAA", 22); break;
+            case 80: memcpy(line_buffer, "11111111AAAA1111111111", 22); break;
+            case 84: memcpy(line_buffer, "111111111AAA1111111111", 22); break;
+            case 88: case 98: memcpy(line_buffer, "11AAAAA111AA11AAAAAAAA", 22); break;
+            case 92: memcpy(line_buffer, "11AAAAAA11AA11AAAAAAAA", 22); break;
+            case 102: memcpy(line_buffer, "111111111AAA11111111AA", 22); break;
+            case 106: memcpy(line_buffer, "11111111AAAA11111111AA", 22); break;
+            case 110: memcpy(line_buffer, "11A111AAAAAA11AAAAAAAA", 22); break;
+            case 114: memcpy(line_buffer, "11AA111AAAAA11AAAAAAAA", 22); break;
+            case 118: memcpy(line_buffer, "11AAA111AAAA11AAAAAAAA", 22); break;
+            case 122: memcpy(line_buffer, "11AAAA111AAA11AAAAAAAA", 22); break;
+            case 126: memcpy(line_buffer, "11AAAAA111AA1111111111", 22); break;
+            case 130: memcpy(line_buffer, "11AAAAAA11AA1111111111", 22); break;
+        }
+        line_buffer[60] = (current_line > 50 && current_line < 100) ? WHITE : BLACK;
+
+        if (current_line > 200 && current_line % 8 == 0) {
+            const uint8_t current_number = frame >> 2;
+            for (uint8_t i = 0; i < 8; ++i) {
+                line_buffer[i] = ((current_number >> i) & 0x1) ? WHITE : BLACK;
+            }
+        }
+    }
+}