Slow breathing animation on two wires, finally working

flake.nix

@@ -90,6 +90,7 @@
             (packages."x86_64-linux"."radio-rx" { gcc = "${avr.gcc}/bin/avr-gcc"; cflags = mcu_cflags atmega32u4; })
             (packages."x86_64-linux"."lantern" { gcc = "${avr.gcc}/bin/avr-gcc"; cflags = mcu_cflags atmega32u4; avr = true; })
             (packages."x86_64-linux"."lantern-controller" { gcc = "${avr.gcc}/bin/avr-gcc"; cflags = mcu_cflags atmega32u4; avr = true; })
+            (packages."x86_64-linux"."tron-bag" { gcc = "${avr.gcc}/bin/avr-gcc"; cflags = mcu_cflags attiny85; avr = true; })
           ];
         };
 
@@ -284,6 +285,29 @@
           ];
         };
 
+      packages."x86_64-linux"."tron-bag_" =
+      let
+        pkgs = import nixpkgs { system = "x86_64-linux"; };
+        avr = pkgs.pkgsCross.avr.buildPackages;
+      in packages."x86_64-linux"."tron-bag" { gcc = "${avr.gcc}/bin/avr-gcc"; cflags = mcu_cflags attiny85; avr = true; };
+      packages."x86_64-linux"."tron-bag" =
+        { gcc, cflags, avr }:
+        let
+          pkgs = import nixpkgs { system = "x86_64-linux"; };
+        in mkProgram {
+          pkgs = pkgs;
+          gcc = gcc;
+          cflags = cflags;
+          pname = "tron-bag";
+          psrc = ./tron-bag;
+          inherit avr;
+
+          pbuildInputs = [
+            (packages."x86_64-linux"."dio" { inherit gcc cflags; })
+            pkgs.pkgsCross.avr.buildPackages.simavr
+          ];
+        };
+
       devShell."x86_64-linux" =
         let
           pkgs = import nixpkgs { system = "x86_64-linux"; };

tron-bag/main.c

@@ -0,0 +1,52 @@
+#include <avr/interrupt.h>
+#include <avr/sleep.h>
+#include <dio.h>
+
+#define FPS                 10
+#define FPS_MS              1000 / FPS
+#define MULT                5
+
+typedef struct {
+    uint8_t value;
+    int8_t inc;
+} counter_t;
+
+void counter_update(counter_t *self) {
+    int16_t value = self->value;
+    value += self->inc;
+
+    if (value >= 255) {
+        self->value = 255;
+        self->inc = -1;
+    } else if (value <= 0) {
+        self->value = 0;
+        self->inc = 1;
+    } else {
+        self->value = value;
+    }
+}
+
+int main(void) {
+    DDRB = 0xff;
+    PORTB = 0;
+
+    GTCCR = 0;
+    TCCR0A = _BV(COM0A1) | _BV(COM0B1) | _BV(WGM01) | _BV(WGM00);
+    TCCR0B = _BV(CS00);
+
+    counter_t red = (counter_t){ .value = 128, .inc = 1 };
+    counter_t blue = (counter_t){ .value = 0, .inc = 1 };
+
+    while(1) {
+        OCR0A = red.value;
+        OCR0B = blue.value;
+
+        _delay_ms(10);
+
+        counter_update(&red);
+        counter_update(&blue);
+    }
+
+    return 0;
+}
+