From f0b4d796297cd4be311b8596c8308bad218adabd Mon Sep 17 00:00:00 2001
From: Dean Camera <dean@fourwalledcubicle.com>
Date: Wed, 16 Dec 2009 08:03:04 +0000
Subject: [PATCH] Slightly speed up software USART in the AVRISP project -
faster parity computation, ensure received data is byte aligned when receive
is complete by throwing away the start bit during reception.
---
Projects/AVRISP/Lib/PDITarget.c | 20 +++++++++++++-------
Projects/AVRISP/Lib/PDITarget.h | 12 +++++++++++-
Projects/AVRISP/makefile | 2 +-
3 files changed, 25 insertions(+), 9 deletions(-)
diff --git a/Projects/AVRISP/Lib/PDITarget.c b/Projects/AVRISP/Lib/PDITarget.c
index a8fe21e9b..e21942a1f 100644
--- a/Projects/AVRISP/Lib/PDITarget.c
+++ b/Projects/AVRISP/Lib/PDITarget.c
@@ -70,8 +70,10 @@ ISR(TIMER1_COMPA_vect, ISR_BLOCK)
if ((SoftUSART_BitCount == BITS_IN_FRAME) && (BITBANG_PDIDATA_PIN & BITBANG_PDIDATA_MASK))
return;
+ /* Shift in the bit one less than the frame size in position, so that the start bit will eventually
+ * be discarded leaving the data to be byte-aligned for quick access */
if (BITBANG_PDIDATA_PIN & BITBANG_PDIDATA_MASK)
- SoftUSART_Data |= (1 << BITS_IN_FRAME);
+ SoftUSART_Data |= (1 << (BITS_IN_FRAME - 1));
SoftUSART_Data >>= 1;
SoftUSART_BitCount--;
@@ -82,6 +84,7 @@ ISR(TIMER1_COMPA_vect, ISR_BLOCK)
if (!IsSending)
return;
+ /* Set the data line to the next bit value */
if (SoftUSART_Data & 0x01)
BITBANG_PDIDATA_PORT |= BITBANG_PDIDATA_MASK;
else
@@ -196,17 +199,20 @@ void PDITarget_SendByte(uint8_t Byte)
bool EvenParityBit = false;
uint8_t ParityData = Byte;
- /* Compute Even parity bit */
- for (uint8_t i = 0; i < 8; i++)
+ /* Compute Even parity - while a bit is still set, chop off lowest bit and toggle parity bit */
+ while (ParityData)
{
- EvenParityBit ^= ParityData & 0x01;
- ParityData >>= 1;
+ EvenParityBit ^= true;
+ ParityData &= (ParityData - 1);
}
+ /* Calculate the new USART frame data here while while we wait for a previous byte (if any) to finish sending */
+ uint16_t NewUSARTData = ((1 << 11) | (1 << 10) | ((uint16_t)EvenParityBit << 9) | ((uint16_t)Byte << 1) | (0 << 0));
+
while (SoftUSART_BitCount);
/* Data shifted out LSB first, START DATA PARITY STOP STOP */
- SoftUSART_Data = ((uint16_t)EvenParityBit << 9) | ((uint16_t)Byte << 1) | (1 << 10) | (1 << 11);
+ SoftUSART_Data = NewUSARTData;
SoftUSART_BitCount = BITS_IN_FRAME;
#endif
}
@@ -253,7 +259,7 @@ uint8_t PDITarget_ReceiveByte(void)
while (SoftUSART_BitCount);
/* Throw away the start, parity and stop bits to leave only the data */
- return (uint8_t)(SoftUSART_Data >> 1);
+ return (uint8_t)SoftUSART_Data;
#endif
}
diff --git a/Projects/AVRISP/Lib/PDITarget.h b/Projects/AVRISP/Lib/PDITarget.h
index 03083fcb6..2a704b3d8 100644
--- a/Projects/AVRISP/Lib/PDITarget.h
+++ b/Projects/AVRISP/Lib/PDITarget.h
@@ -54,7 +54,17 @@
/* Defines: */
#if ((BOARD == BOARD_XPLAIN) || (BOARD == BOARD_XPLAIN_REV1))
- #define PDI_VIA_HARDWARE_USART
+// #define PDI_VIA_HARDWARE_USART
+
+ #define BITBANG_PDIDATA_PORT PORTD
+ #define BITBANG_PDIDATA_DDR DDRD
+ #define BITBANG_PDIDATA_PIN PIND
+ #define BITBANG_PDIDATA_MASK (1 << 3)
+
+ #define BITBANG_PDICLOCK_PORT PORTD
+ #define BITBANG_PDICLOCK_DDR DDRD
+ #define BITBANG_PDICLOCK_PIN PIND
+ #define BITBANG_PDICLOCK_MASK (1 << 5)
#else
#define BITBANG_PDIDATA_PORT PORTB
#define BITBANG_PDIDATA_DDR DDRB
diff --git a/Projects/AVRISP/makefile b/Projects/AVRISP/makefile
index 2b6a1e858..23e27c52d 100644
--- a/Projects/AVRISP/makefile
+++ b/Projects/AVRISP/makefile
@@ -66,7 +66,7 @@ MCU = at90usb1287
# Target board (see library "Board Types" documentation, USER or blank for projects not requiring
# LUFA board drivers). If USER is selected, put custom board drivers in a directory called
# "Board" inside the application directory.
-BOARD = USBKEY
+BOARD = XPLAIN
# Processor frequency.
--
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