From b79c868668720901c31599451ea1e92320605e26 Mon Sep 17 00:00:00 2001
From: Nicolae Hodos <nicu@hodos.ro>
Date: Sat, 21 Jan 2017 22:37:10 +0100
Subject: [PATCH] filter for raspberry pi

---
 pre_filter/pre_filter.ino | 261 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 261 insertions(+)
 create mode 100644 pre_filter/pre_filter.ino

diff --git a/pre_filter/pre_filter.ino b/pre_filter/pre_filter.ino
new file mode 100644
index 0000000..1485d13
--- /dev/null
+++ b/pre_filter/pre_filter.ino
@@ -0,0 +1,261 @@
+/* attiny45 - 433 MHz prefilter - V 3.0 - written by mercuri0 & CurlyMo */
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <avr/power.h>
+#include <avr/wdt.h>
+
+#define bool            _Bool
+#define true            1
+#define false           0
+
+#define CAT(a, ...)       PRIMITIVE_CAT(a, __VA_ARGS__)
+#define PRIMITIVE_CAT(a, ...)   a ## __VA_ARGS__
+
+#define SET(a,b)        a |=  _BV(b)
+#define CLEAR(a,b)        a &= ~_BV(b)
+#define HIGH(a,b)       SET(a,b)
+#define LOW(a,b)        CLEAR(a,b)
+#define GET(a,b)        a & _BV(b)
+#define TOGGLE(a,b)       a ^= _BV(b)
+
+#define SET_OUTPUT(a,b)     a |= _BV(b)
+#define SET_INPUT(a,b)      a &= ~_BV(b)
+
+#define D_PORT          DDRB
+#define D_PIN(a)        PRIMITIVE_CAT(DDB,a)
+
+#define V_PORT          PORTB
+#define V_PIN(a)        PRIMITIVE_CAT(PORTB,a)
+
+#define REC_OUT         4
+#define PI_IN           3
+
+#define MIN_PULSELENGTH     8     //tested to work down to 30us pulsewidth (=2)
+#define MAX_PULSELENGTH     1600
+#define PLSLEN          183
+#define REPEATS         2
+#define VERSION         3
+
+volatile uint16_t         ten_us_counter = 0;
+volatile unsigned long      ten_us_counter1 = 0;
+volatile uint8_t        valid_buffer = 0x00;
+volatile uint8_t        checksum = 0;
+
+volatile uint16_t         bit = 0;
+volatile uint8_t        state = 0;
+volatile uint8_t        lsb = 0;
+volatile uint8_t        nrrepeat = 0;
+
+volatile uint16_t         _version = 0;
+volatile uint16_t         _minplslen = 0;
+volatile uint16_t         _maxplslen = 0;
+volatile uint8_t        _chksum = 0;
+
+void get_mcusr(void) __attribute__((naked)) __attribute__((section(".init3")));
+void get_mcusr(void) {
+  MCUSR = 0;
+  wdt_disable();
+}
+
+void init_system(void){
+  cli();
+
+  SET(TCCR1, CS12);
+  SET(TCCR1, CTC1);
+  OCR1A = OCR1C = 0x14;
+  SET(TIMSK, OCIE1A);
+
+  SET(PCMSK, PCINT4);
+  SET(MCUCR, ISC00);
+  SET(GIMSK, PCIE);
+
+  SET_OUTPUT(D_PORT, D_PIN(PI_IN));
+  CLEAR(V_PORT, V_PIN(PI_IN));
+
+  sei();
+
+  power_adc_disable();
+  power_usi_disable();
+  power_timer0_disable();
+
+  wdt_enable(WDTO_4S);
+  
+  int hpf = MAX_PULSELENGTH;
+  int lpf = MIN_PULSELENGTH;
+  int ver = VERSION;
+  while(hpf > 10) hpf /= 10;
+  while(lpf > 10) lpf /= 10;
+  while(ver > 10) ver /= 10;
+  checksum = ((ver&0xf)+(lpf&0xf)+(hpf&0xf))&0xf;
+  _chksum = checksum;
+}
+
+int main (void)
+{
+  init_system();
+
+  while(1) {
+    asm volatile("NOP");
+  }
+}
+
+void send() {
+  TOGGLE(V_PORT, V_PIN(PI_IN));
+  ten_us_counter1 = 0;
+  state ^= 1;
+}
+
+void send1(int len) {
+  if(ten_us_counter1 > len) {
+    send();
+    bit++;
+  }
+}
+
+void send2(int len) {
+  if(ten_us_counter1 > len) {
+    send();
+    lsb++;
+  }
+}
+
+void shift(int a) {
+  lsb = 0;
+  bit++;
+  switch(a) {
+    case 1:
+      _version >>= 1;
+    break;
+    case 2:
+      _minplslen >>= 1;
+    break;
+    case 3:
+      _maxplslen >>= 1;
+    break;
+    case 4:
+      _chksum >>= 1;
+    break;
+  }
+}
+
+void reset() {
+  _version = VERSION;
+  _minplslen = MIN_PULSELENGTH;
+  _maxplslen = MAX_PULSELENGTH;
+  _chksum = checksum;
+  bit = 0;
+  ten_us_counter1 = 0;
+  lsb = 0;
+}
+
+void sendHigh() {
+  if(lsb == 1) {
+    send2((PLSLEN*3)/10);
+  } else {
+    send2(PLSLEN/10);
+  }
+}
+
+void sendLow() {
+  if(lsb == 3) {
+    send2((PLSLEN*3)/10);
+  } else {
+    send2(PLSLEN/10);
+  }
+}
+
+ISR(TIMER1_COMPA_vect){
+  wdt_reset();
+  ten_us_counter++;
+  ten_us_counter1++;
+  if(nrrepeat >= REPEATS && ten_us_counter1 >= 6000000) {
+    reset();
+    if(state == 1) {
+      send();
+    }
+    nrrepeat = 0;
+  }
+  if(nrrepeat < REPEATS) {
+    cli();
+    if(bit < 56) {
+      if(bit < 2) {
+        if(state == 0) {
+          send1(PLSLEN/10);
+        } else {
+          send1((PLSLEN*6)/10);
+        }
+      } else if(bit < 18) {
+        if((_version&0x0000000000000001) == 1) {
+          sendHigh();
+        } else {
+          sendLow();
+        }
+        if(lsb == 4) {
+          shift(1);
+        }
+      } else if(bit < 34) {
+        if((_minplslen&0x0000000000000001) == 1) {
+          sendHigh();
+        } else {
+          sendLow();
+        }
+        if(lsb == 4) {
+          shift(2);
+        }
+      } else if(bit < 50) {
+        if((_maxplslen&0x0000000000000001) == 1) {
+          sendHigh();
+        } else {
+          sendLow();
+        }
+        if(lsb == 4) {
+          shift(3);
+        }
+      }  else if(bit < 54) {
+        if((_chksum&0x0001) == 1) {
+          sendHigh();
+        } else {
+          sendLow();
+        }
+        if(lsb == 4) {
+          shift(4);
+        }
+      } else {
+        if(state == 0) {
+          send1(PLSLEN/10);
+        } else {
+          send1((PLSLEN*34)/10);
+        }
+      }
+    } else {
+      nrrepeat++;
+      reset();
+      if(state == 1) {
+        send();
+      }
+    }
+  } else {
+    sei();
+  }
+}
+
+ISR(PCINT0_vect){
+  cli();
+  valid_buffer <<= 1;
+  if(ten_us_counter > MIN_PULSELENGTH)
+  {
+    if(ten_us_counter < MAX_PULSELENGTH)
+    {
+      valid_buffer |= 0x01;
+      if (valid_buffer == 0xFF)
+      {
+        state ^= 1;
+        TOGGLE(V_PORT, V_PIN(PI_IN));
+      }
+    }
+  }
+  ten_us_counter = 0;
+  TCNT1 = 0;
+  sei();
+}
+