From 61e96805add5df3ceade89eaafed4695fa31a422 Mon Sep 17 00:00:00 2001
From: marshmellow42 <marshmellowrf@gmail.com>
Date: Fri, 9 Feb 2018 15:49:55 -0500
Subject: [PATCH 1/1] add bitbang option to lf cmdread

by setting delay to 0 we can use cmd binary to bitbang the antenna.

note that the timing isn't perfect (especially on the off periods) but
is fairly close. worst i've seen it off is 8us on a large off period.
but i don't have the best test equipment...
---
 armsrc/lfops.c | 79 ++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 63 insertions(+), 16 deletions(-)

diff --git a/armsrc/lfops.c b/armsrc/lfops.c
index 4344742b..5e9fb193 100644
--- a/armsrc/lfops.c
+++ b/armsrc/lfops.c
@@ -29,6 +29,7 @@
 void ModThenAcquireRawAdcSamples125k(uint32_t delay_off, uint32_t period_0, uint32_t period_1, uint8_t *command)
 {
 
+	StartTicks();
 	int divisor_used = 95; // 125 KHz
 	// see if 'h' was specified
 
@@ -43,36 +44,82 @@ void ModThenAcquireRawAdcSamples125k(uint32_t delay_off, uint32_t period_0, uint
 	/* Make sure the tag is reset */
 	FpgaDownloadAndGo(FPGA_BITSTREAM_LF);
 	FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
-	SpinDelay(2500);
+	WaitMS(2500);
 
+	//power on
 	LFSetupFPGAForADC(sc.divisor, 1);
 
 	// And a little more time for the tag to fully power up
-	SpinDelay(2000);
-
+	WaitMS(2000);
+	// if delay_off = 0 then just bitbang 1 = antenna on 0 = off for respective periods.
+	bool bitbang = delay_off == 0;
 	// now modulate the reader field
-	while(*command != '\0' && *command != ' ') {
+
+	if (bitbang) {
+		//HACK it appears my loop and if statements take up about 7 us so adjust waits accordingly...
+		uint8_t hack_cnt = 7;
+		if (period_0 < hack_cnt || period_1 < hack_cnt) {
+			DbpString("Warning periods cannot be less than 7 in bit bang mode");
+			FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
+			LED_D_OFF();
+			return;
+		}
+		//prime cmd_len to save time comparing strings while modulating
+		int cmd_len = 0;
+		while(command[cmd_len] != '\0' && command[cmd_len] != ' ')
+			cmd_len++;
+
+		int counter = 0;
+		bool off = false;
+		for (counter = 0; counter < cmd_len; counter++) {
+		//while(*command != '\0' && *command != ' ') {
+			// if cmd = 0 then turn field off
+			if (command[counter] == '0') {
+				// if field already off leave alone (affects timing otherwise)
+				if (off == false) {
+					FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
+					LED_D_OFF();
+					off = true;
+				}
+				// note we appear to take about 6us to switch over (or run the if statements/loop...)
+				WaitUS(period_0-hack_cnt);
+			// else if cmd = 1 then turn field on
+			} else {
+				// if field already on leave alone (affects timing otherwise)
+				if (off) {
+					FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_ADC | FPGA_LF_ADC_READER_FIELD);				
+					LED_D_ON();
+					off = false;
+				}
+				// note we appear to take about 6us to switch over (or run the if statements/loop...)
+				WaitUS(period_1-hack_cnt);
+			}
+		}
+	} else { // old mode of cmd read using delay as off period
+		while(*command != '\0' && *command != ' ') {
+			FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
+			LED_D_OFF();
+			WaitUS(delay_off);
+			FpgaSendCommand(FPGA_CMD_SET_DIVISOR, sc.divisor);
+			FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_ADC | FPGA_LF_ADC_READER_FIELD);
+			LED_D_ON();
+			if(*(command++) == '0') {
+				WaitUS(period_0);
+			} else {
+				WaitUS(period_1);
+			}
+		}
 		FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
 		LED_D_OFF();
-		SpinDelayUs(delay_off);
+		WaitUS(delay_off);
 		FpgaSendCommand(FPGA_CMD_SET_DIVISOR, sc.divisor);
-
-		FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_ADC | FPGA_LF_ADC_READER_FIELD);
-		LED_D_ON();
-		if(*(command++) == '0')
-			SpinDelayUs(period_0);
-		else
-			SpinDelayUs(period_1);
 	}
-	FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
-	LED_D_OFF();
-	SpinDelayUs(delay_off);
-	FpgaSendCommand(FPGA_CMD_SET_DIVISOR, sc.divisor);
 
 	FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_ADC | FPGA_LF_ADC_READER_FIELD);
 
 	// now do the read
 	DoAcquisition_config(false, 0);
+	// note leaves field on...  (for future commands?)
 }
 
 /* blank r/w tag data stream
-- 
2.39.5