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SendOnlySoftwareSerial.cpp
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SendOnlySoftwareSerial.cpp
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/*
SendOnlySoftwareSerial - adapted from SendOnlySoftwareSerial by Nick Gammon 30th December 2016
SoftwareSerial.cpp (formerly NewSoftSerial.cpp) -
Multi-instance software serial library for Arduino/Wiring
-- Interrupt-driven receive and other improvements by ladyada
(http://ladyada.net)
-- Tuning, circular buffer, derivation from class Print/Stream,
multi-instance support, porting to 8MHz processors,
various optimizations, PROGMEM delay tables, inverse logic and
direct port writing by Mikal Hart (http://www.arduiniana.org)
-- Pin change interrupt macros by Paul Stoffregen (http://www.pjrc.com)
-- 20MHz processor support by Garrett Mace (http://www.macetech.com)
-- ATmega1280/2560 support by Brett Hagman (http://www.roguerobotics.com/)
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
The latest version of this library can always be found at
http://arduiniana.org.
*/
// When set, _DEBUG co-opts pins 11 and 13 for debugging with an
// oscilloscope or logic analyzer. Beware: it also slightly modifies
// the bit times, so don't rely on it too much at high baud rates
#define _DEBUG 0
#define _DEBUG_PIN1 11
#define _DEBUG_PIN2 13
//
// Includes
//
#include <avr/interrupt.h>
#include <avr/pgmspace.h>
#include <Arduino.h>
#include <SendOnlySoftwareSerial.h>
#include <util/delay_basic.h>
//
// Debugging
//
// This function generates a brief pulse
// for debugging or measuring on an oscilloscope.
#if _DEBUG
inline void DebugPulse(uint8_t pin, uint8_t count)
{
volatile uint8_t *pport = portOutputRegister(digitalPinToPort(pin));
uint8_t val = *pport;
while (count--)
{
*pport = val | digitalPinToBitMask(pin);
*pport = val;
}
}
#else
inline void DebugPulse(uint8_t, uint8_t) {}
#endif
//
// Private methods
//
/* static */
inline void SendOnlySoftwareSerial::tunedDelay(uint16_t delay) {
_delay_loop_2(delay);
}
//
// Constructor
//
SendOnlySoftwareSerial::SendOnlySoftwareSerial(uint8_t transmitPin, bool inverse_logic /* = false */) :
_tx_delay(0),
_inverse_logic(inverse_logic)
{
setTX(transmitPin);
}
//
// Destructor
//
SendOnlySoftwareSerial::~SendOnlySoftwareSerial()
{
end();
}
void SendOnlySoftwareSerial::setTX(uint8_t tx)
{
// First write, then set output. If we do this the other way around,
// the pin would be output low for a short while before switching to
// output high. Now, it is input with pullup for a short while, which
// is fine. With inverse logic, either order is fine.
digitalWrite(tx, _inverse_logic ? LOW : HIGH);
pinMode(tx, OUTPUT);
_transmitBitMask = digitalPinToBitMask(tx);
uint8_t port = digitalPinToPort(tx);
_transmitPortRegister = portOutputRegister(port);
}
uint16_t SendOnlySoftwareSerial::subtract_cap(uint16_t num, uint16_t sub) {
if (num > sub)
return num - sub;
else
return 1;
}
//
// Public methods
//
void SendOnlySoftwareSerial::begin(long speed)
{
_tx_delay = 0;
// Precalculate the various delays, in number of 4-cycle delays
uint16_t bit_delay = (F_CPU / speed) / 4;
// 12 (gcc 4.8.2) or 13 (gcc 4.3.2) cycles from start bit to first bit,
// 15 (gcc 4.8.2) or 16 (gcc 4.3.2) cycles between bits,
// 12 (gcc 4.8.2) or 14 (gcc 4.3.2) cycles from last bit to stop bit
// These are all close enough to just use 15 cycles, since the inter-bit
// timings are the most critical (deviations stack 8 times)
_tx_delay = subtract_cap(bit_delay, 15 / 4);
#if _DEBUG
pinMode(_DEBUG_PIN1, OUTPUT);
pinMode(_DEBUG_PIN2, OUTPUT);
#endif
}
void SendOnlySoftwareSerial::end()
{
}
size_t SendOnlySoftwareSerial::write(uint8_t b)
{
if (_tx_delay == 0) {
setWriteError();
return 0;
}
// By declaring these as local variables, the compiler will put them
// in registers _before_ disabling interrupts and entering the
// critical timing sections below, which makes it a lot easier to
// verify the cycle timings
volatile uint8_t *reg = _transmitPortRegister;
uint8_t reg_mask = _transmitBitMask;
uint8_t inv_mask = ~_transmitBitMask;
uint8_t oldSREG = SREG;
bool inv = _inverse_logic;
uint16_t delay = _tx_delay;
if (inv)
b = ~b;
cli(); // turn off interrupts for a clean txmit
// Write the start bit
if (inv)
*reg |= reg_mask;
else
*reg &= inv_mask;
tunedDelay(delay);
// Write each of the 8 bits
for (uint8_t i = 8; i > 0; --i)
{
if (b & 1) // choose bit
*reg |= reg_mask; // send 1
else
*reg &= inv_mask; // send 0
tunedDelay(delay);
b >>= 1;
}
// restore pin to natural state
if (inv)
*reg &= inv_mask;
else
*reg |= reg_mask;
SREG = oldSREG; // turn interrupts back on
tunedDelay(_tx_delay);
return 1;
}
void SendOnlySoftwareSerial::flush()
{
// There is no tx buffering, simply return
}
// Read data from buffer
int SendOnlySoftwareSerial::read()
{
return -1;
}
int SendOnlySoftwareSerial::available()
{
return 0;
}
int SendOnlySoftwareSerial::peek()
{
return -1;
}