Rudimentary host-to-device implementation

ardkbd.c

@@ -6,8 +6,10 @@
 #include <stdint.h>
 
 
-static volatile uint8_t kbd_state = 0;
+static volatile int8_t kbd_state = 0;
+
 static volatile uint8_t kbd_input = 0;
+static volatile uint8_t kbd_output = 0;
 static volatile uint8_t kbd_flags = 0;
 
 
@@ -38,6 +40,40 @@ ISR(PCINT1_vect) {
 	if (kbd_clock())
 		return;
 
+	if (kbd_state < 0) {
+		if (kbd_state >= -8) {
+			if (kbd_output & (1 << (-1-kbd_state)))
+				PORTC |= 0x01;
+			else
+				PORTC &= ~0x01;
+
+			kbd_state--;
+			return;
+		}
+
+		if (kbd_state == -9) {
+			if ((__builtin_popcount(kbd_output) & 1) == 0)
+				PORTC |= 0x01;
+			else
+				PORTC &= ~0x01;
+
+			kbd_state--;
+			return;
+		}
+
+		if (kbd_state == -10) {
+			kbd_state--;
+
+			DDRC &= ~0x01;
+			PORTC |= 0x01;
+			return;
+		}
+
+		kbd_state = 0;
+
+		return;
+	}
+
 	bool data = kbd_data();
 
 	if (kbd_state == 0) {
@@ -94,7 +130,6 @@ ISR(PCINT1_vect) {
 		case KBD_CODE_DOWN:
 			if (ts < 31)
 				ts++;
-			PORTB = 0;
 			break;
 		}
 	}
@@ -102,6 +137,31 @@ ISR(PCINT1_vect) {
 	kbd_flags = 0;
 }
 
+
+void kbd_send(uint8_t command) {
+	while (kbd_state) {} /* wait for idle */
+
+	DDRC |= 0x02;
+	PORTC &= ~0x02;
+	_delay_us(100);
+
+	DDRC |= 0x01;
+	PORTC &= ~0x01;
+	_delay_us(10);
+
+	DDRC &= ~0x02;
+	PORTC |= 0x02;
+
+	kbd_output = command;
+	kbd_state = -1;
+
+	/* wait for idle */
+	while (kbd_state) {}
+	while (!kbd_state) {}
+	while (kbd_state) {}
+}
+
+
 int main(void) {
 	DDRB  = 0xff;
 	PORTB = 0;
@@ -114,8 +174,20 @@ int main(void) {
 
 	sei();
 
+	kbd_send(0xff);
+
+	uint8_t l = 0;
+
 	while(true) {
-		PORTB ^= 0x20;
+		uint8_t state = PORTB ^ 0x20;
+		PORTB = state;
+
+		if (state & 0x20) {
+			l = (l+1)%3;
+
+			kbd_send(0xed);
+			kbd_send(1 << l);
+		}
 
 		uint32_t i;
 		for (i = 0; i < (1 << ts); i++)