diff --git a/README.md b/README.md
new file mode 100644
index 0000000..9896afb
--- /dev/null
+++ b/README.md
@@ -0,0 +1,41 @@
+# AVR Toolchain
+
+## Prerequisites
+
+```shell
+apt install flex byacc bison build-essential apt install libgmp-dev libmpfr-dev libmpc-dev
+```
+
+## Binutils
+
+```shell
+$ wget http://ftp.gnu.org/gnu/binutils/binutils-2.33.1.tar.xz
+$ tar xvf binutils-2.33.1.tar.xz
+$ cd binutils-2.33.1
+$ ./configure --target=avr --program-prefix="avr-"
+$ make -j4
+$ make install
+```
+
+## GCC
+
+```shell
+$ wget ftp://ftp.fu-berlin.de/unix/languages/gcc/releases/gcc-9.2.0/gcc-9.2.0.tar.xz
+$ tar cvf gcc-9.2.0.tar.xz
+$ mkdir avrgcc-9.2.0
+$ cd avrgcc-9.2.0
+$ ../gcc-9.2.0/configure --target=avr --enable-languages=c,c++ --disable-libssp
+$ make -j4
+$ make install
+```
+
+## avr-libc
+
+```shell
+$ wget http://download.savannah.gnu.org/releases/avr-libc/avr-libc-2.0.0.tar.bz2
+$ tar xvf avr-libc-2.0.0.tar.bz2
+$ cd avr-libc-2.0.0
+$ ./configure --host=avr
+$ make -j4
+$ make install
+```
\ No newline at end of file
diff --git a/src/main.c b/src/main.c
index d8623da..9e305d9 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,37 +1,115 @@
+#include <stdbool.h>
 #include <stdint.h>
 
 #define F_CPU 1000000UL
 
 #include <avr/interrupt.h>
 #include <avr/io.h>
+#include <avr/power.h>
 #include <avr/sleep.h>
 #include <avr/wdt.h>
-#include <util/delay.h>
 
-volatile int tick;
+#define MOSI_PIN        0
+#define MISO_PIN        1
+#define SCK_PIN         2
+#define POWER_PIN       3
+#define IGNITION_PIN    4
 
-int main(void)
+#define SHUTDOWN_TIME_MS 5000UL
+
+#define ignition_on() (PINB & (1 << IGNITION_PIN))
+#define power_on() (PINB & (1 << POWER_PIN))
+
+bool is_shutdown;
+volatile uint32_t tick;
+
+enum power {
+    off = 0,
+    on
+};
+
+void setup_gpio()
 {
-    cli();
-    tick = 0;
     DDRB = 0xff;
+    PORTB = 0;
+    DDRB &= ~(1 << IGNITION_PIN);
+    PORTB |= (1 << IGNITION_PIN);   // enable pull-up
 
+    GIMSK |= (1 << PCIE);           // Enable Pin Change Interrupts
+    PCMSK |= (1 << IGNITION_PIN);   // Use PB4 as interrupt pin
+}
+
+void setup_timer0()
+{
     TCCR0A = (1 << WGM01);
-    TCCR0B = (1 << CS01);
+    TCCR0B = (1 << CS01);   // prescaler = 8
     TIMSK |= (1 << OCIE0A); // enable compare match interrupt
 
     // ((1000000 / 8) / 1000) = 125
     OCR0A = 125 - 1;
+}
 
-    // TIMSK |= (1 << TOIE0);
+void setup_watchdog()
+{
+    MCUSR &= ~(1 << WDRF);
+    WDTCR = (1 << WDCE) | (1 << WDE);
+    WDTCR = (1 << WDIE) | (1 << WDP2) | (1 << WDP1);
+}
+
+void switch_power(enum power power)
+{
+    if(power) {
+        PORTB |= (1 << POWER_PIN);
+    }
+    else {
+        PORTB &= ~(1 << POWER_PIN);
+    }
+}
+
+int main(void)
+{
+    uint32_t shutdown_expire = 0;
+    tick = 0;
+    is_shutdown = false;
+    setup_gpio();
+    setup_timer0();
+
+    ADCSRA = 0;
+    ADCSRB = 0;
+
+    set_sleep_mode(SLEEP_MODE_PWR_DOWN);
 
     sei();
+
     while(1) {
-        if(tick >= 1000) {
-            PORTB ^= (1 << PB4);
-            tick = 0;
+        if(ignition_on()) {
+            if(!power_on()) {
+                switch_power(on);
+                is_shutdown = false;
+            }
+            sleep_enable();
+            sleep_cpu();
+            sleep_disable();
+        } else {
+            if(!is_shutdown) {
+                is_shutdown = true;
+                shutdown_expire = tick + SHUTDOWN_TIME_MS;
+            }
+            else {
+                if(shutdown_expire < tick) {
+                    if(power_on()) {
+                        switch_power(off);
+                    }
+                    // setup_watchdog();
+                    sleep_enable();
+                    sleep_cpu();
+                    sleep_disable();
+                    // wdt_disable();
+                }
+            }
         }
     }
+
     return 0;
 }
 
@@ -39,3 +117,15 @@ ISR(TIM0_COMPA_vect)
 {
     tick++;
 }
+
+// wake up by level interrupt on PB4
+ISR(PCINT0_vect)
+{
+}
+
+// wake up by watchdog interrupt
+ISR(WDT_vect)
+{
+    WDTCR |= (1 << WDIE);
+}
+