From 3fd246041b10609a204a6352aa1b86d7000171d4 Mon Sep 17 00:00:00 2001
From: Dean Camera <dean@fourwalledcubicle.com>
Date: Mon, 12 Jul 2010 02:23:11 +0000
Subject: [PATCH] Add glitch protection to the software UART in the
 XPLAINBridge project code, so that very short glitches on the RX line don't
 cause a frame reception to occur.

---
 Projects/XPLAINBridge/Lib/SoftUART.c | 20 +++++++++++++-------
 Projects/XPLAINBridge/XPLAINBridge.c |  2 +-
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/Projects/XPLAINBridge/Lib/SoftUART.c b/Projects/XPLAINBridge/Lib/SoftUART.c
index 458a505cd2..90c23b71d4 100644
--- a/Projects/XPLAINBridge/Lib/SoftUART.c
+++ b/Projects/XPLAINBridge/Lib/SoftUART.c
@@ -76,15 +76,21 @@ void SoftUART_Init(void)
 /** ISR to detect the start of a bit being sent to the software UART. */
 ISR(INT0_vect, ISR_BLOCK)
 {
-	/* Reset and start the reception timer */
-	TCNT1  = 0;
-	TCCR1B = ((1 << CS10) | (1 << WGM12));
-
 	/* Reset the number of reception bits remaining counter */
 	RX_BitsRemaining = 8;
+	
+	/* Reset the bit reception timer */
+	TCNT1 = 0;
+
+	/* Check to see that the pin is still low (prevents glitches from starting a frame reception) */
+	if (!(SRXPIN & (1 << SRX)))
+	{
+		/* Disable start bit detection ISR while the next byte is received */
+		EIMSK = 0;
 
-	/* Disable start bit detection ISR while the next byte is received */
-	EIMSK = 0;
+		/* Start the reception timer */
+		TCCR1B = ((1 << CS10) | (1 << WGM12));
+	}
 }
 
 /** ISR to manage the reception of bits to the software UART. */
@@ -133,7 +139,7 @@ ISR(TIMER3_COMPA_vect, ISR_NOBLOCK)
 		TX_Data >>= 1;
 		TX_BitsRemaining--;
 	}
-	else if (USBtoUART_Buffer.Count)
+	else if (USBtoUART_Buffer.Count && !(RX_BitsRemaining))
 	{
 		/* Start bit - TX line low */
 		STXPORT &= ~(1 << STX);
diff --git a/Projects/XPLAINBridge/XPLAINBridge.c b/Projects/XPLAINBridge/XPLAINBridge.c
index c08dfe980c..1f0070319f 100644
--- a/Projects/XPLAINBridge/XPLAINBridge.c
+++ b/Projects/XPLAINBridge/XPLAINBridge.c
@@ -180,7 +180,7 @@ void EVENT_USB_Device_ConfigurationChanged(void)
 	{
 		EndpointConfigSuccess &= CDC_Device_ConfigureEndpoints(&VirtualSerial_CDC_Interface);
 
-		/* Configure the UART flush timer */
+		/* Configure the UART flush timer - run at FCPU/1024 for maximum interval before overflow */
 		TCCR0B = ((1 << CS02) | (1 << CS00));
 	}
 	else