Slightly speed up software USART in the AVRISP project - faster parity computation...

[pub/lufa.git] / Projects / AVRISP / Lib / PDITarget.c

diff --git a/Projects/AVRISP/Lib/PDITarget.c b/Projects/AVRISP/Lib/PDITarget.c
index a8fe21e..e21942a 100644 (file)
--- 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))\r
                  return;\r
        \r
                if ((SoftUSART_BitCount == BITS_IN_FRAME) && (BITBANG_PDIDATA_PIN & BITBANG_PDIDATA_MASK))\r
                  return;\r
        \r

+               /* Shift in the bit one less than the frame size in position, so that the start bit will eventually\r
+                * be discarded leaving the data to be byte-aligned for quick access */\r

                if (BITBANG_PDIDATA_PIN & BITBANG_PDIDATA_MASK)\r
                if (BITBANG_PDIDATA_PIN & BITBANG_PDIDATA_MASK)\r

-                 SoftUSART_Data |= (1 << BITS_IN_FRAME);\r
+                 SoftUSART_Data |= (1 << (BITS_IN_FRAME - 1));\r

 \r
                SoftUSART_Data >>= 1;\r
                SoftUSART_BitCount--;\r
 \r
                SoftUSART_Data >>= 1;\r
                SoftUSART_BitCount--;\r


@@ -82,6 +84,7 @@ ISR(TIMER1_COMPA_vect, ISR_BLOCK)
                if (!IsSending)\r
                  return;\r
 \r
                if (!IsSending)\r
                  return;\r
 \r

+               /* Set the data line to the next bit value */\r

                if (SoftUSART_Data & 0x01)\r
                  BITBANG_PDIDATA_PORT |=  BITBANG_PDIDATA_MASK;\r
                else\r
                if (SoftUSART_Data & 0x01)\r
                  BITBANG_PDIDATA_PORT |=  BITBANG_PDIDATA_MASK;\r
                else\r


@@ -196,17 +199,20 @@ void PDITarget_SendByte(uint8_t Byte)
        bool    EvenParityBit = false;\r
        uint8_t ParityData    = Byte;\r
 \r
        bool    EvenParityBit = false;\r
        uint8_t ParityData    = Byte;\r
 \r

-       /* Compute Even parity bit */\r
-       for (uint8_t i = 0; i < 8; i++)\r
+       /* Compute Even parity - while a bit is still set, chop off lowest bit and toggle parity bit */\r
+       while (ParityData)\r

        {\r
        {\r

-               EvenParityBit ^= ParityData & 0x01;\r
-               ParityData    >>= 1;\r
+               EvenParityBit ^= true;\r
+               ParityData    &= (ParityData - 1);\r

        }\r
 \r
        }\r
 \r

+       /* Calculate the new USART frame data here while while we wait for a previous byte (if any) to finish sending */\r
+       uint16_t NewUSARTData = ((1 << 11) | (1 << 10) | ((uint16_t)EvenParityBit << 9) | ((uint16_t)Byte << 1) | (0 << 0));\r
+\r

        while (SoftUSART_BitCount);\r
 \r
        /* Data shifted out LSB first, START DATA PARITY STOP STOP */\r
        while (SoftUSART_BitCount);\r
 \r
        /* Data shifted out LSB first, START DATA PARITY STOP STOP */\r

-       SoftUSART_Data     = ((uint16_t)EvenParityBit << 9) | ((uint16_t)Byte << 1) | (1 << 10) | (1 << 11);\r
+       SoftUSART_Data     = NewUSARTData;\r

        SoftUSART_BitCount = BITS_IN_FRAME;\r
 #endif\r
 }\r
        SoftUSART_BitCount = BITS_IN_FRAME;\r
 #endif\r
 }\r


@@ -253,7 +259,7 @@ uint8_t PDITarget_ReceiveByte(void)
        while (SoftUSART_BitCount);\r
        \r
        /* Throw away the start, parity and stop bits to leave only the data */\r
        while (SoftUSART_BitCount);\r
        \r
        /* Throw away the start, parity and stop bits to leave only the data */\r

-       return (uint8_t)(SoftUSART_Data >> 1);\r
+       return (uint8_t)SoftUSART_Data;\r

 #endif\r
 }\r
 \r
 #endif\r
 }\r
 \r