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AltSoftSerial.cpp

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+/******************************************************************************
+ * @file    AltSoftSerial.h
+ * @author  Rémi Pincent - INRIA
+ * @date    24 nov. 2015   
+ *
+ * @brief Bit-Banging uart
+ * 
+ * Project : AltSoftSerial
+ * Contact:  Rémi Pincent - remi.pincent@inria.fr
+ * 
+ * Originally from
+ * 
+ * LICENSE :
+ * AltSoftSerial (c) by Rémi Pincent
+ * AltSoftSerial is licensed under a
+ * Creative Commons Attribution-NonCommercial 3.0 Unported License.
+ *
+ * You should have received a copy of the license along with this
+ * work.  If not, see <http://creativecommons.org/licenses/by-nc/3.0/>.
+ *
+ * ORIGINALLY FROM :
+ * An Alternative Software Serial Library
+ * http://www.pjrc.com/teensy/td_libs_AltSoftSerial.html
+ * Copyright (c) 2014 PJRC.COM, LLC, Paul Stoffregen, paul@pjrc.com
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ *****************************************************************************/
+
+#include "AltSoftSerial.h"
+#include "pinout.h"
+extern "C"{
+#include "nrf_gpio.h"
+#include "app_error.h"
+}
+
+/****************************************/
+/**          Defines                   **/
+/****************************************/
+#define UART_STOP_BIT_POS       8
+#define UART_STOP_BIT_ACTIVE    1
+
+/****************************************/
+/**          Variables                 **/
+/****************************************/
+AltSoftSerial AltSoftSerial::SoftSerial = AltSoftSerial();
+
+/****************************************/
+/**          Initialization            **/
+/****************************************/
+
+AltSoftSerial::AltSoftSerial() : _u8_txPin(INVALID_PIN),
+		_u16_ticks_per_bit(0),
+		_b_uartBusy(false),
+		timing_error(false),
+		_u8_sendByte(0),
+		_txBuffer(TX_BUFFER_SIZE)
+{
+
+}
+
+void AltSoftSerial::initTimer(void)
+{
+	/** Use TIMER 2 - Also used by Arduino Tone object */
+	/** MUST not use TIMER0 : used by soft_device */
+	NRF_TIMER2->MODE = TIMER_MODE_MODE_Timer;               // Set the timer in Timer Mode.
+	NRF_TIMER2->PRESCALER = 0;                              // Prescaler 0 produces F_CPU/2^prescaler timer frequency => 1 tick = 32 us.
+	NRF_TIMER2->BITMODE     = TIMER_BITMODE_BITMODE_16Bit;  // 16 bit mode
+	NRF_TIMER2->SHORTS = TIMER_SHORTS_COMPARE0_CLEAR_Msk;   // Short to lear IT
+	NRF_TIMER2->TASKS_CLEAR = 1;                            // clear the task first to be usable for later.
+	NRF_TIMER2->INTENSET = TIMER_INTENSET_COMPARE0_Msk;     // Enable IT
+	NRF_TIMER2->CC[0] = _u16_ticks_per_bit;
+
+	IntController_linkInterrupt( TIMER2_IRQn, AltSoftSerial::txTimerIRQ);
+
+    if(!IntController_enableIRQ(TIMER2_IRQn, NRF_APP_PRIORITY_LOW))
+    {
+    	APP_ERROR_CHECK_BOOL(false);
+    }
+}
+
+void AltSoftSerial::stopTimer(void)
+{
+	NRF_TIMER2->TASKS_STOP = 1;
+	NRF_TIMER2->INTENCLR = TIMER_INTENSET_COMPARE0_Disabled << TIMER_INTENCLR_COMPARE0_Pos;
+}
+
+void AltSoftSerial::begin(uint32_t baud, uint8_t txPin)
+{
+	_u8_txPin = arduinoToVariantPin(txPin);
+	_u16_ticks_per_bit = F_CPU / baud;
+
+	initTimer();
+	pinMode(_u8_txPin, OUTPUT);
+	digitalWrite(txPin, HIGH);
+}
+
+void AltSoftSerial::end(void)
+{
+	flushOutput();
+	stopTimer();
+}
+
+
+/****************************************/
+/**           Transmission             **/
+/****************************************/
+
+bool AltSoftSerial::writeByte(uint8_t b)
+{
+	if(_txBuffer.pushElement(b) != RingBuffer<uint8_t>::NO_ERROR)
+	{
+		/** May be buffer full... */
+		return false;
+	}
+
+    if (!_b_uartBusy)
+    {
+    	_b_uartBusy = true;
+    	_txBuffer.popElement(SoftSerial._u8_sendByte);
+
+        // We set start bit active (low)
+    	digitalWrite(_u8_txPin, LOW);
+        NRF_TIMER2->TASKS_START = 1;
+    }
+    else
+    {
+    	/** UART busy but byte added to RING buffer */
+    }
+    return true;
+}
+
+
+void AltSoftSerial::flushOutput(void)
+{
+	while (_b_uartBusy) /* wait */ ;
+}
+
+/**
+ * Bit-Bang ring buffer bytes. No parity, start and stop bits, 8 bits
+ *
+ *   ______________________________________________________________
+ *  | start bit | d0 | d1 | d2 | d3 | d4 | d5 | d6 | d7 | stop bit |
+ *  |___________|____|____|____|____|____|____|____|____|__________|
+ *
+ */
+void AltSoftSerial::txTimerIRQ()
+{
+    if(NRF_TIMER2->EVENTS_COMPARE[0])
+    {
+        static uint8_t bit_pos;
+        NRF_TIMER2->EVENTS_COMPARE[0] = 0;
+
+        if (bit_pos < UART_STOP_BIT_POS)
+        {
+        	/** set bit at bit_pos */
+            (SoftSerial._u8_sendByte & (1 << bit_pos)) ? digitalWrite(SoftSerial._u8_txPin, HIGH) : digitalWrite(SoftSerial._u8_txPin, LOW);;
+            bit_pos++;
+        }
+        else if (bit_pos == UART_STOP_BIT_POS)
+        {
+            bit_pos++;
+            /** Set stop bit */
+            digitalWrite(SoftSerial._u8_txPin, HIGH);
+        }
+        // We have to wait until STOP bit is finished before releasing m_uart_busy.
+        else if (bit_pos == UART_STOP_BIT_POS + 1)
+        {
+            bit_pos = 0;
+            if(!SoftSerial._txBuffer.elementsAvailable())
+            {
+            	/** no more byte to write to UART */
+            	NRF_TIMER2->TASKS_STOP = 1;
+            	SoftSerial._b_uartBusy = false;
+            	SoftSerial._u8_sendByte = 0;
+            	return;
+            }
+            else
+            {
+            	/** still some bytes to write to UART */
+            	SoftSerial._txBuffer.popElement(SoftSerial._u8_sendByte);
+            	digitalWrite(SoftSerial._u8_txPin, LOW);
+            }
+        }
+    }
+}
+
+
+

AltSoftSerial.h

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+/******************************************************************************
+ * @file    AltSoftSerial.h 
+ * @author  Rémi Pincent - INRIA
+ * @date    24 nov. 2015   
+ *
+ * @brief Bit-Banging uart - Tx buffered
+ * 
+ * Project : AltSoftSerial
+ * Contact:  Rémi Pincent - remi.pincent@inria.fr
+ * 
+ * Originally from
+ * 
+ * LICENSE :
+ * AltSoftSerial (c) by Rémi Pincent
+ * AltSoftSerial is licensed under a
+ * Creative Commons Attribution-NonCommercial 3.0 Unported License.
+ *
+ * You should have received a copy of the license along with this
+ * work.  If not, see <http://creativecommons.org/licenses/by-nc/3.0/>.
+ *
+ * ORIGINALLY FROM :
+ * An Alternative Software Serial Library
+ * http://www.pjrc.com/teensy/td_libs_AltSoftSerial.html
+ * Copyright (c) 2014 PJRC.COM, LLC, Paul Stoffregen, paul@pjrc.com
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ *****************************************************************************/
+
+#ifndef AltSoftSerial_h
+#define AltSoftSerial_h
+
+#include <inttypes.h>
+#include <ring_buffer.h>
+
+#if ARDUINO >= 100
+#include "Arduino.h"
+#else
+#include "WProgram.h"
+#include "pins_arduino.h"
+#endif
+
+class AltSoftSerial : public Stream
+{
+private :
+	static const uint8_t TX_BUFFER_SIZE = 40;
+
+	uint8_t _u8_txPin;
+	uint16_t _u16_ticks_per_bit;
+	bool _b_uartBusy;
+	bool timing_error;
+	uint8_t _u8_sendByte;
+	RingBuffer<uint8_t> _txBuffer;
+
+public:
+	/** instance */
+	static AltSoftSerial SoftSerial;
+
+public:
+	AltSoftSerial();
+	 virtual ~AltSoftSerial() { end(); }
+	void begin(uint32_t baud, uint8_t txPin);
+	void end();
+	/** RX not implemented */
+	int peek(){return 0;};
+	/** RX not implemented */
+	int read(){return 0;};
+	/** RX not implemented */
+	int available(){return 0;};
+#if ARDUINO >= 100
+	size_t write(uint8_t byte) { writeByte(byte); return 1; }
+	void flush() { flushOutput(); }
+#else
+	void write(uint8_t byte) { writeByte(byte); }
+	void flush() { flushInput(); }
+#endif
+	using Print::write;
+	/** RX not implemented */
+	void flushInput(){return;};
+	void flushOutput();
+	// for drop-in compatibility with NewSoftSerial, rxPin & txPin ignored
+	AltSoftSerial(uint8_t rxPin, uint8_t txPin, bool inverse = false) : AltSoftSerial() { }
+	bool listen() { return false; }
+	bool isListening() { return true; }
+	bool overflow() { bool r = timing_error; timing_error = false; return r; }
+	static int library_version() { return 1; }
+
+private:
+	void initTimer(void);
+	void stopTimer(void);
+	bool writeByte(uint8_t byte);
+	static void txTimerIRQ(void);
+};
+
+#endif

README.md

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+# Description
+Bit-banging UART
+
+# Supported platforms
+* Nordic nrf51 
+
+## Limitations
+* only tx Supported
+* bad bit banging when Radio active, e.g when advertising. Timer used for bit banging has lower priority than BLE.
+
+# Code sample
+
+    AltSoftSerial::SoftSerial.begin(9600, TX_PIN);
+    AltSoftSerial::SoftSerial.println("Hello from AltSoftSerial);
+
+# References
+https://github.com/PaulStoffregen/AltSoftSerial