From 678adc33f84beb91dbc44dd38729df155d880003 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Fri, 1 Nov 2013 00:11:49 +0200
Subject: [PATCH] Use pin change interrupt to react faster to the clock

---
 s88w/s88w-r.c | 109 ++++++++++++++++++++++++++------------------------
 1 file changed, 57 insertions(+), 52 deletions(-)

diff --git a/s88w/s88w-r.c b/s88w/s88w-r.c
index 15365b4..1716532 100644
--- a/s88w/s88w-r.c
+++ b/s88w/s88w-r.c
@@ -37,26 +37,27 @@ void check_input();
 uint8_t hexdigit(uint8_t);
 uint8_t decode_hex(uint8_t);
 
-volatile uint8_t rx_buf[7];
-volatile uint8_t rx_fill = 0xFF;
-volatile uint8_t input[128] = { 0 };
-volatile uint8_t latch[128] = { 0 };
-volatile uint8_t lcd_enabled = 0;
+uint8_t clock_high = 0;
+uint8_t rx_buf[7];
+uint8_t rx_fill = 0xFF;
+uint8_t input[128] = { 0 };
+uint8_t latch[128] = { 0 };
+uint8_t out_offset = 0;
+uint8_t out_bits = 0;
+uint8_t out_fill = 0;
+volatile uint8_t reset_pos = 0xFF;
+uint8_t lcd_enabled = 0;
 uint8_t log_row = 0;
 uint8_t log_col = 0;
 
 int main()
 {
-	uint8_t clock_high = 0;
-	uint8_t bits = 0;
-	uint8_t n_bits = 8;
-	uint8_t offset = 0;
-	uint8_t i;
-
 	DDRD = 0x06;   // 00000110
 	PORTD = 0xC0;  // 11000000
 	DDRB = 0x20;   // 00100000
 	PORTB = 0x1F;  // 00011111
+	PCMSK2 = BIT(PCINT19) | BIT(PCINT21);
+	PCICR = BIT(PCIE2);
 
 	serial_init(9600);
 	lcd_init();
@@ -65,53 +66,20 @@ int main()
 
 	while(1)
 	{
-		uint8_t b_pins, d_pins;
+		uint8_t i;
 
 		check_input();
 
-		b_pins = PINB;
-		d_pins = PIND;
-
-		if(d_pins&BIT(CLOCK))
+		i = reset_pos;
+		if(i!=0xFF)
 		{
-			if(!clock_high)
-			{
-				if(d_pins&BIT(LOAD))
-				{
-					offset = 0;
-					bits = latch[0];
-					n_bits = 8;
-				}
-				else
-				{
-					bits >>= 1;
-					if(!--n_bits)
-					{
-						++offset;
-						bits = latch[offset];
-						n_bits = 8;
-					}
-				}
-
-				if(bits&1)
-					PORTD |= BIT(DATA_OUT);
-				else
-					PORTD &= ~BIT(DATA_OUT);
-
-				clock_high = 1;
-			}
+			latch[i] = input[i];
+			if(++i>=sizeof(input))
+				i = 0xFF;
+			reset_pos = i;
 		}
-		else if(clock_high)
-			clock_high = 0;
 
-		if(d_pins&BIT(RESET))
-		{
-			uint8_t i;
-			for(i=0; i<128; ++i)
-				latch[i] = input[i];
-		}
-
-		if(b_pins&BIT(LCD_DISABLE))
+		if(PINB&BIT(LCD_DISABLE))
 		{
 			if(lcd_enabled)
 			{
@@ -222,3 +190,40 @@ uint8_t decode_hex(uint8_t c)
 	else
 		return 0;
 }
+
+ISR(PCINT2_vect)
+{
+	uint8_t d = PIND;
+	if(d&BIT(CLOCK))
+	{
+		if(!clock_high)
+		{
+			if(d&BIT(LOAD))
+			{
+				out_offset = 0;
+				out_bits = latch[0];
+				out_fill = 8;
+			}
+
+			if(out_bits&1)
+				PORTD |= BIT(DATA_OUT);
+			else
+				PORTD &= ~BIT(DATA_OUT);
+
+			out_bits >>= 1;
+			if(!--out_fill)
+			{
+				++out_offset;
+				out_bits = latch[out_offset];
+				out_fill = 8;
+			}
+
+			clock_high = 1;
+		}
+	}
+	else
+		clock_high = 0;
+
+	if(d&BIT(RESET))
+		reset_pos = 0;
+}
-- 
2.45.2