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#include <Arduino.h>
#include "hcs200.h"
/** Pulse width lengths used by the transmitter. A pulse width is the time
* between a transition from 0 to 1 or from 1 to 0 of the input pin.
*/
enum RbType
{
RB_SHORT = 0, // pulse_width
RB_LONG, // 2 * pulse_width
RB_ERROR
};
/** Determine if 'pulse' is a short pulse, RB_SHORT or a long one, RB_LONG.
* Normally, a short pulse is the same as the 'tx_clock' and a long pulse is
* twice as long. However, timing problems with servicing interrupts means
* that we need to add some fudge factors.
*/
int HCS200::classify(unsigned pulse)
{
int d = pulse - tx_clock;
if (d < -100)
return RB_ERROR;
else if (d < 100)
return RB_SHORT;
else
{
d -= tx_clock;
if (d < -100)
return RB_ERROR;
else if (d < 100)
return RB_LONG;
else
return RB_ERROR;
}
}
#define IN_RANGE(x, min, max) (x >= min && x <= max)
void HCS200::on_isr(uint8_t value)
{
unsigned long timestamp = micros();
unsigned long pulse_width = timestamp - last_timestamp;
int d;
switch (rx_state) {
case RS_PREAMBLE_START:
// value == 0
preamble_count = 1;
rx_state = RS_PREAMBLE_LOW;
tx_clock = pulse_width;
break;
case RS_PREAMBLE_LOW:
// value == 1
preamble_count++;
d = pulse_width - tx_clock;
rx_state = (IN_RANGE(d, -100, 100)) ? RS_PREAMBLE_HIGH : RS_NOSYNC;
break;
case RS_PREAMBLE_HIGH:
// value == 0
preamble_count++;
d = pulse_width - tx_clock;
if (IN_RANGE(d, -100, 100))
rx_state = (preamble_count == 23) ? RS_PREAMBLE_HEADER : RS_PREAMBLE_LOW;
else
rx_state = RS_NOSYNC;
break;
case RS_PREAMBLE_HEADER:
// header should be low for 10*tx_clock
d = pulse_width - 10 * tx_clock;
if (value == 1 && IN_RANGE(d, -100, 100))
{
rx_state = RS_DATA;
rx_bit_count = 0;
memset(rx_buf, 0, sizeof(rx_buf));
}
else
rx_state = RS_NOSYNC;
break;
case RS_DATA:
if (value == 1)
{
int first = classify(last_pulse_width);
int second = classify(pulse_width);
// received a 1 bit
if (first == RB_SHORT && second == RB_LONG)
{
int idx = rx_bit_count / 32;
rx_buf[idx] >>= 1;
rx_buf[idx] |= 0x80000000;
rx_bit_count++;
}
// received a 0 bit
else if (first == RB_LONG && second == RB_SHORT)
{
int idx = rx_bit_count / 32;
rx_buf[idx] >>= 1;
rx_bit_count++;
}
else
rx_state = RS_NOSYNC;
// we ignore the last bit as it's always "1"
// instead we use the raising edge as trigger to stop
if (rx_bit_count == MAX_BITS - 1)
rx_state = RS_COMPLETED;
}
break;
}
// check outside of the state machine
// this is important as otherwise otherwise we always miss the start
if (rx_state == RS_NOSYNC && value == 1)
rx_state = RS_PREAMBLE_START;
last_timestamp = timestamp;
last_pulse_width = pulse_width;
}
void HCS200::reset()
{
rx_state = RS_NOSYNC;
}
bool HCS200::decode(HCS200_Keycode &out)
{
if (rx_state != RS_COMPLETED)
return false;
out.encrypted = rx_buf[0];
out.serial = rx_buf[1] & 0x0FFFFFFF;
out.buttons = (rx_buf[1] >> 28) & 0xF;
out.lowbat = rx_buf[2] & 0x80000000;
return true;
}
void HCS200::print_state(Print &stream)
{
stream.print("rx_state=");
stream.print(rx_state, DEC);
stream.print(", rx_bit_count=");
Serial.print(rx_bit_count, DEC);
stream.print(", tx_clock=");
stream.print(tx_clock, DEC);
stream.print(", preamble_count=");
stream.println(preamble_count, DEC);
}
void HCS200_Keycode::print(Print &stream)
{
stream.print("Keyfob# ");
stream.print(serial, HEX);
stream.print(", buttons:");
if (buttons & BM_S0)
stream.print(" 1");
if (buttons & BM_S1)
stream.print(" 2");
if (buttons & BM_S2)
stream.print(" 3");
if (buttons & BM_S3)
stream.print(" 4");
stream.print(", lowbat=");
stream.print(lowbat, DEC);
stream.print(", code=");
stream.print(encrypted, HEX);
stream.print("\n");
}
#define PULSE_WIDTH 440
inline void HCS200_Keycode::send(bool value, std::function<void(int)> setOutput)
{
if (!value)
{
setOutput(HIGH);
delayMicroseconds(PULSE_WIDTH);
delayMicroseconds(PULSE_WIDTH);
setOutput(LOW);
delayMicroseconds(PULSE_WIDTH);
}
else
{
setOutput(HIGH);
delayMicroseconds(PULSE_WIDTH);
setOutput(LOW);
delayMicroseconds(PULSE_WIDTH);
delayMicroseconds(PULSE_WIDTH);
}
}
void HCS200_Keycode::send(std::function<void(int)> setOutput)
{
uint32_t val;
// preamble
for(unsigned short i = 0; i < 11; i++)
{
setOutput(HIGH);
delayMicroseconds(PULSE_WIDTH);
setOutput(LOW);
delayMicroseconds(PULSE_WIDTH);
}
setOutput(HIGH);
delayMicroseconds(PULSE_WIDTH);
// header
setOutput(LOW);
delayMicroseconds(PULSE_WIDTH * 10);
// encrypted
val = this->encrypted;
for(unsigned short i = 0; i < 32; i++)
{
send(val & 0x01, setOutput);
val >>= 1;
}
// serial
val = this->serial;
for(unsigned short i = 0; i < 28; i++)
{
send(val & 0x01, setOutput);
val >>= 1;
}
// buttons
val = this->buttons;
for(unsigned short i = 0; i < 4; i++)
{
send(val & 0x01, setOutput);
val >>= 1;
}
// lowbat
send(this->lowbat, setOutput);
// RPT
send(1, setOutput);
// guard time
setOutput(LOW);
delayMicroseconds(PULSE_WIDTH * 39);
}
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