From 75b588a288d080336d760217a7cd8ea6c0e5900c Mon Sep 17 00:00:00 2001
From: XANTRONIX Development <dev@xantronix.com>
Date: Wed, 1 Jun 2016 23:40:40 -0500
Subject: [PATCH] Yikes, did I actually make a thing that might be used to talk
 to the Game Boy Printer?  I think so.

---
 avr/Makefile |   7 ++-
 avr/send.c   | 131 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 134 insertions(+), 4 deletions(-)

diff --git a/avr/Makefile b/avr/Makefile
index 7ade12e..459e5fc 100644
--- a/avr/Makefile
+++ b/avr/Makefile
@@ -54,8 +54,11 @@ $(RECV_ELF): $(RECV_OBJS)
 $(OBJS): %.o: %.c $(HEADERS_BUILD)
 	$(CC) $(CFLAGS) -c $<
 
-flash: $(IMAGE_BIN)
-	$(AVRDUDE) $(AVRDUDE_FLAGS) -U flash:w:$(IMAGE_BIN):r
+flash-send: $(SEND_BIN)
+	$(AVRDUDE) $(AVRDUDE_FLAGS) -U flash:w:$(SEND_BIN):r
+
+flash-recv: $(RECV_BIN)
+	$(AVRDUDE) $(AVRDUDE_FLAGS) -U flash:w:$(RECV_BIN):r
 
 clean:
 	$(RM) -f $(IMAGES_BIN) $(IMAGES_ELF) $(OBJS)
diff --git a/avr/send.c b/avr/send.c
index 7411ded..a662623 100644
--- a/avr/send.c
+++ b/avr/send.c
@@ -1,11 +1,13 @@
 #include <avr/io.h>
 #include <avr/interrupt.h>
+#include <avr/sleep.h>
 #include <util/delay.h>
 
 #include <tabby/printer.h>
 #include <tabby/avr/uart.h>
 
-#define TIMER0_INTERVAL 1953
+#define TIMER0_INTERVAL  1953
+#define PACKET_BODY_SIZE  640
 
 static volatile uint8_t bits      = 0;
 static volatile uint8_t value_in  = 0x00; /* Data coming in from Game Boy */
@@ -17,6 +19,14 @@ static volatile tabby_printer_packet header = {
     .size        = 0
 };
 
+static volatile uint8_t body[PACKET_BODY_SIZE];
+
+static volatile uint16_t sum = 0x0000;
+
+static volatile uint8_t device   = 0x00,
+                        status   = 0x00,
+                        buffered = 0;
+
 static volatile uint16_t i = 0,
                          b = 0;
 
@@ -24,6 +34,10 @@ static volatile uint16_t i = 0,
  * Internal clock source interrupt vector
  */
 ISR(TIMER0_COMPB_vect) {
+    if (!buffered) {
+        reti();
+    }
+
     value_in >>= 1;
 
     PORTB |= (1 << PORTB5);
@@ -41,6 +55,29 @@ ISR(TIMER0_COMPB_vect) {
     value_out <<= 1;
 
     if (--bits == 0) {
+        if (i < sizeof(header)) {
+            value_out = header.data[i++];
+        } else if (b < header.size) {
+            value_out = body[b++];
+        } else if (b == header.size) {
+            value_out = sum & 0x00ff;
+            b++;
+        } else if (b == header.size + 1) {
+            value_out = (sum & 0xff00) >> 8;
+            b++;
+        } else if (b == header.size + 2) {
+            device    = value_in;
+            value_out = 0x00;
+            b++;
+        } else if (b == header.size + 3) {
+            status    = value_in;
+            value_out = 0x00;
+
+            i        = 0;
+            b        = 0;
+            buffered = 0;
+        }
+
         bits = 8;
     }
 
@@ -90,7 +127,24 @@ static void clock_setup() {
     TCCR1B = (1 << CS10);
 }
 
+static uint16_t checksum() {
+    uint16_t sum = 0;
+    size_t i;
+
+    for (i=2; i<6; i++) {
+        sum += header.data[i];
+    }
+
+    for (i=0; i<header.size; i++) {
+        sum += body[i];
+    }
+
+    return sum;
+}
+
 int main() {
+    uint16_t sum = 0;
+
     uart_init();
 
     clock_setup();
@@ -98,8 +152,81 @@ int main() {
     sei();
 
     while (1) {
-        uint8_t c = uart_getchar(NULL);
+        uint8_t c;
 
+        while (buffered) {
+            sleep_mode();
+        }
+
+        c = uart_getchar(NULL);
+
+        switch (i) {
+            case 0: {
+                if (c == 0x88) {
+                    header.data[0] = c;
+                    i++;
+
+                    b = 0;
+                }
+
+                break;
+            }
+
+            case 1: {
+                if (c == 0x33) {
+                    header.data[1] = c;
+                    i++;
+                } else {
+                    i = 0;
+                }
+
+                break;
+            }
+
+            case 2: {
+                header.type = c;
+                i++;
+
+                break;
+            }
+
+            case 3: {
+                header.compression = c;
+                i++;
+
+                break;
+            }
+
+            case 4: {
+                header.size = c;
+                i++;
+
+                break;
+            }
+
+            case 5: {
+                header.size |= c << 8;
+                i++;
+
+                break;
+            }
+
+            default: {
+                if (b < header.size) {
+                    b++;
+                } else if (b == header.size) {
+                    sum = c;
+                } else if (b == header.size + 1) {
+                    sum |= c << 8;
+
+                    if (sum == checksum()) {
+                        i        = 0;
+                        b        = 0;
+                        buffered = 1;
+                    }
+                }
+            }
+        }
     }
 
     return 0;