From: Drew Fisher <drew.m.fisher@gmail.com>
Date: Mon, 22 Feb 2010 19:44:40 +0000 (-0500)
Subject: Convert SNES polling to a timer interrupt-based routine, update comments.
X-Git-Url: https://git.zarvox.org/shortlog/month?a=commitdiff_plain;h=8d593537dd5c74d9c41dd963f594b3874fb1420f;p=usbsnes.git

Convert SNES polling to a timer interrupt-based routine, update comments.
---

diff --git a/main.c b/main.c
index 6a8ff6b..236766c 100644
--- a/main.c
+++ b/main.c
@@ -27,11 +27,16 @@ PROGMEM char usbHidReportDescriptor[28] = {
 	0xc0,        //   END_COLLECTION
 	0xc0         // END_COLLECTION
 };
-
+/*
 typedef struct {
 	uchar buttons[2];
 } report_t;
+*/
+typedef struct {
+	uint16_t buttons;
+} report_t;
 
+static report_t buttonState;
 static report_t reportBuffer;
 
 usbMsgLen_t usbFunctionSetup(uchar data[8]) {
@@ -53,10 +58,31 @@ usbMsgLen_t usbFunctionSetup(uchar data[8]) {
 	return 0;   /* default for not implemented requests: return no data back to host */
 }
 
+ISR(TIMER1_COMPA) {
+	buttonState.buttons = pollSnes();
+}
+
+void initTimer() {
+	// See section 15.11 for reference
+	// Using CTC mode (non-PWM)
+
+	// TCCR1A = 0b00000000 (No timer output, no PWM)
+	// TCCR1B = 0b00001010 (CTC mode, ckli_o/8)
+	// TCCR1C = 0b00000000 (No output compare)
+	TCCR1A = 0b00000000;
+	TCCR1B = 0b00001010;
+	TCCR1C = 0b00000000;
+	// {OCR1AH, OCR1AL} = 37500 = 10010010 01111100
+	// 37500 * 8 * 60 = 18MHz
+	OCR1AH = 0b10010010;
+	OCR1AL = 0b01111000;
+	// TIMSK1 = 0b00000010 (Enable interrupt on Output Compare A Match)
+	TIMSK1 = 0b00000010;
+}
+
 int main(void)
 {
 	uchar i;
-
 	wdt_enable(WDTO_1S); // Enable watchdog with 1s reset time
 	/* Even if you don't use the watchdog, turn it off here. On newer devices,
 	 * the status of the watchdog (on/off, period) is PRESERVED OVER RESET!
@@ -66,9 +92,18 @@ int main(void)
 	
 	/* RESET status: all port bits are inputs without pull-up.
 	 * That's the way we need D+ and D-. Therefore we don't need any
-	 * additional hardware initialization.
+	 * additional hardware initialization on the USB side.
 	 */
 	
+	// We need to setup the pin configuration for D3, which is an output pin 
+	
+
+	// Set up the clock prescaler to CLKI_O/8, which gives us 2250000 ticks per second
+	// This makes 37500 such ticks give us a 60Hz signal, which is exactly how we set up
+	// the timer interrupt to poll the SNES controller
+	
+
+
 	//odDebugInit();
 	
 	usbInit();
@@ -86,7 +121,7 @@ int main(void)
 		wdt_reset();
 		usbPoll();
 		if(usbInterruptIsReady()){
-			pollSnes();
+			reportBuffer.buttons = buttonState.buttons;
 			/* called after every poll of the interrupt endpoint */
 			//advanceCircleByFixedAngle();
 			//DBG1(0x03, 0, 0);   /* debug output: interrupt report prepared */
diff --git a/snes.S b/snes.S
index 02e385b..bac54a0 100644
--- a/snes.S
+++ b/snes.S
@@ -153,8 +153,8 @@ readbitsecond8:
 
 invertvalues:
 	ldi temp2, 0xff ; for xor
-	eor resL, temp2 ; Invert for negative logic
-	eor resH, temp2 ; Remember, low indicates button pressed.
+	eor resL, temp2 ; Invert for negative logic - to the SNES controller,
+	eor resH, temp2 ; low indicates button pressed.  To USB HID, the opposite.
 	ret		; return to caller
 
 unconnected:		; Controller was disconnected