From 97e0ff26faf90fa257fd64034502d8a3fa4a59a9 Mon Sep 17 00:00:00 2001
From: giomba <giomba@glgprograms.it>
Date: Sat, 26 Jun 2021 23:42:23 +0200
Subject: [PATCH] "diagonal line"

not the whole screen, but vertically locked
actually it has some issues, there is a single dot (at the
end/beginning of a cycle) that messes up the horizontal sync and moves
all the picture... must be fixed
---
 main.S | 40 +++++++++++++++++++++++++++++++---------
 main.c | 15 ++++-----------
 2 files changed, 35 insertions(+), 20 deletions(-)

diff --git a/main.S b/main.S
index 47ee4a0..ee11340 100644
--- a/main.S
+++ b/main.S
@@ -9,6 +9,9 @@ status:
 offset:
 .byte 78
 
+line:
+.word 0
+
 .text
 
 .global main_s
@@ -21,10 +24,10 @@ main_s:
     out IO(MCUCR), r16
     out IO(MCUCR), r17
 
-    ldi r16, 0x3        ; enable falling edge interrupt 0
+    ldi r16, 0xa        ; external interrupt 0 and 1, falling edge
     sts EICRA, r16
 
-    ldi r16, 0x1        ; external interrupt mask enable
+    ldi r16, 0x3        ; external interrupt 0 and 1, mask enable
     sts EIMSK, r16
 
     sei
@@ -66,26 +69,33 @@ wait2:
 
     jmp again
 
-.global int0_handler
-int0_handler:
+.global int_horizontal_sync
+int_horizontal_sync:
     push r31
     in r31, IO(SREG)    ; status register
     push r31
 
+    lds r31, line
+    cpi r31, 255
+    brsh int_horizontal_sync_end
+    inc r31
+    sts line, r31
+
+    lds r31, status
+    cpi r31, 0
+    brne int_horizontal_sync_end
+
     lds r31, offset
     dec r31
     cpi r31, 1
     brne 1f
-    ldi r31, 78
+    ldi r31, 140
 1:
     sts offset, r31
 loop:
     dec r31
     brne loop
 
-    lds r31, status
-    cpi r31, 1
-    brne 1f
     sbi IO(PORTB), 4
     nop
     nop
@@ -98,9 +108,21 @@ loop:
     nop
     nop
     cbi IO(PORTB), 4
-1:
+
+int_horizontal_sync_end:
     pop r31
     out IO(SREG), r31
     pop r31
     reti
 
+.global int_vertical_sync
+int_vertical_sync:
+    push r31
+    ldi r31, 0
+    sts line, r31
+    ldi r31, 140
+    sts offset, r31
+    pop r31
+    reti
+
+
diff --git a/main.c b/main.c
index f795dd1..f509ba1 100644
--- a/main.c
+++ b/main.c
@@ -2,20 +2,13 @@
 #include <avr/interrupt.h>
 
 void main_s(void);
-void int0_handler(void);
-
-void pippo() {
-    asm("nop");
-    asm("push r1");
-    int i = 0;
-    i = 2;
-    i += 1;
-    reti();
-}
 
 
 ISR(INT0_vect, ISR_NAKED) {
-    asm("jmp int0_handler");
+    asm("jmp int_vertical_sync");
+}
+ISR(INT1_vect, ISR_NAKED) {
+    asm("jmp int_horizontal_sync");
 }
 
 int main() {