Move different experiments to different files

Makefile

+# This Makefile compiles and flashes four different programs:
+# - led_on
+# - button_contact
+# - timer_test
+# - button_toggle
+#
+# To program a board, first make sure the PROGRAMMER variable is set correctly.
+# (If you're using your own HTM(a)A programmer board, use usbtiny.) Each board
+# will also have to have its fuses set once, which can be done by running
+# "make program-fuses". Finally, run make program_<program_name>. For example,
+# "make program_button_toggle" will build and flash the button_toggle program.
+
+MMCU=attiny44
+F_CPU = 20000000
+CFLAGS=-mmcu=$(MMCU) -Wall -Os -DF_CPU=$(F_CPU)
+PROGRAMMER = atmelice_isp
+
+%.hex: %.out
+	avr-objcopy -O ihex $< $@;\
+	avr-size --mcu=$(MMCU) --format=avr $@
+ 
+%.out: %.c
+	avr-gcc $(CFLAGS) -I./ -o $@ $<
+ 
+program_%: %.hex
+	avrdude -p t44 -P usb -c $(PROGRAMMER) -U flash:w:$<
+
+.PHONY: default
+default: program_button_toggle
+
+program-fuses:
+	avrdude -p t44 -P usb -c $(PROGRAMMER) -U lfuse:w:0x5E:m
+

button_contact.c

+#include <avr/io.h>
+
+#define led_pin (1 << PB2)
+#define button_pin (1 << PA7)
+
+int main(void) {
+    // Configure led_pin as an output.
+    DDRB |= led_pin;
+
+    // Configure button_pin as an output.
+    DDRA &= ~button_pin;
+
+    // Activate button_pin's pullup resistor.
+    PORTA |= button_pin;
+
+    // Nothing left to do, so just spin.
+    while (1) {
+        // Turn on the LED when the button is pressed.
+        if (PINA & button_pin) {
+            // Turn off the LED.
+            PORTB &= ~led_pin;
+        } else {
+            PORTB |= led_pin;
+        }
+    }
+
+    return 0;
+}
+

blink.c → button_toggle.c

 #include <avr/io.h>
 
-#define switch_pin (1 << PA7)
 #define led_pin (1 << PB2)
+#define button_pin (1 << PA7)
 
 int main(void) {
     // Set the clock prescaler to 1.
@@ -14,65 +14,36 @@ int main(void) {
     // Configure led_pin as an output.
     DDRB |= led_pin;
 
-    // Configure switch_pin as an input.
-    DDRA |= switch_pin;
+    // Configure button_pin as an output.
+    DDRA &= ~button_pin;
 
-    // Activate switch_pin's pullup resistor.
-    PORTA |= switch_pin;
-
-    //int count1 = 0;
-    //int count2 = 0;
+    // Activate button_pin's pullup resistor.
+    PORTA |= button_pin;
 
     int bouncy_switch_state = 0;
     int debounced_switch_state = 0;
 
+    // Nothing left to do, so just spin.
     while (1) {
-        // Turn on the led when the button is pressed
-        /*
-        if (PINA & switch_pin) {
-            PORTB &= ~led_pin;
-        } else {
-            PORTB |= led_pin;
-        }
-        */
-
-        // ~5s blink period based on counting
-        /*
-        if (++count1 == 255) {
-            if (++count2 == 255) {
-                PORTB ^= led_pin;
-                count1 = 0;
-                count2 = 0;
-            }
-        }
-        */
-
-        // ~2.5s second blink period
-        // 255 * 200 * (1024 / 20M) = 2.6112
-        /*
-        if (TCNT0 >= 200) {
+        // Use the timer to count how long it's been since button_pin changed state.
+        if ((PINA & button_pin) != bouncy_switch_state) {
+            bouncy_switch_state = PINA & button_pin;
             TCNT0 = 0;
-            if (++count1 == 255) {
-                PORTB ^= led_pin;
-                count1 = 0;
-            }
         }
-        */
 
-        // the button toggles the led (with debouncing)
-        if ((PINA & switch_pin) != bouncy_switch_state) {
-            bouncy_switch_state = PINA & switch_pin;
-            TCNT0 = 0;
-        }
+        // If it's been 10ms or more since PA7 changed state, // it's not bouncing.
         if (TCNT0 >= 195) {
             // It's been 10ms since the switch changed.
             if (bouncy_switch_state != debounced_switch_state) {
                 debounced_switch_state = bouncy_switch_state;
+                // If the button is newly pressed, toggle the LED.
                 if (debounced_switch_state == 0) {
                     PORTB ^= led_pin;
                 }
             }
         }
     }
+
+    return 0;
 }
 

led_on.c

+#include <avr/io.h>
+
+#define led_pin (1 << PB2)
+
+int main(void) {
+    // Configure led_pin as an output.
+    DDRB |= led_pin;
+
+    // Set led_pin high.
+    PORTB |= led_pin;
+
+    // Nothing left to do, so just spin.
+    while (1) {}
+
+    return 0;
+}
+

timer_test.c

+#include <avr/io.h>
+
+#define led_pin (1 << PB2)
+
+int main(void) {
+    // Set the clock prescaler to 1.
+    CLKPR = (1 << CLKPCE);
+    CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);
+
+    // Set the 8 bit timer's prescaler to 1/1024.
+    TCCR0B |= 0b00000101;
+
+    // Configure led_pin as an output.
+    DDRB |= led_pin;
+
+    // Blink the LED with ~2.5s half-period.
+    // 250 * 200 * 1024 / 20M ~ 2.5s
+    int count = 0;
+    while (1) {
+        // If it's been 10ms, reset the timer and increment count.
+        if (TCNT0 >= 200) {
+            TCNT0 = 0;
+            // When count reaches 250, reset it and toggle the LED.
+            if (++count == 250) {
+                PORTB ^= led_pin;
+                count = 0;
+            }
+        }
+    }
+
+    return 0;
+}
+