Button debouncing with bitshifting.

button_debounce_shift/Makefile

@@ -0,0 +1,501 @@
+# ----------------------------------------------------------------------------
+# Makefile based on WinAVR Makefile Template written by Eric B. Weddington, 
+# Jörg Wunsch, et al.
+#
+# Adjust F_CPU below to the clock frequency in Mhz of your AVR target
+#
+# Adjust the size of the uart receive and transmit ringbuffer in bytes using 
+# defines -DUART_RX_BUFFER_SIZE=128 and -DUART_TX_BUFFER_SIZE=128 in the 
+# CDEF section below
+# 
+#----------------------------------------------------------------------------
+# On command line:
+#
+# make all = Make software.
+#
+# make clean = Clean out built project files.
+#
+# make coff = Convert ELF to AVR COFF.
+#
+# make extcoff = Convert ELF to AVR Extended COFF.
+#
+# make program = Download the hex file to the device, using avrdude.
+#                Please customize the avrdude settings below first!
+#
+# make debug = Start either simulavr or avarice as specified for debugging, 
+#              with avr-gdb or avr-insight as the front end for debugging.
+#
+# make filename.s = Just compile filename.c into the assembler code only.
+#
+# make filename.i = Create a preprocessed source file for use in submitting
+#                   bug reports to the GCC project.
+#
+# To rebuild project do "make clean" then "make all".
+#----------------------------------------------------------------------------
+
+
+# MCU name
+MCU = atmega328p
+
+# Processor frequency.
+#     This will define a symbol, F_CPU, in all source code files equal to the 
+#     processor frequency. You can then use this symbol in your source code to 
+#     calculate timings. Do NOT tack on a 'UL' at the end, this will be done
+#     automatically to create a 32-bit value in your source code.
+F_CPU = 16000000
+
+# Output format. (can be srec, ihex, binary)
+FORMAT = ihex
+
+# Target file name (without extension).
+TARGET = main
+
+# List C source files here. (C dependencies are automatically generated.) 
+SRC = $(TARGET).c uart_async.c timer.c
+
+# List Assembler source files here.
+#     Make them always end in a capital .S.  Files ending in a lowercase .s
+#     will not be considered source files but generated files (assembler
+#     output from the compiler), and will be deleted upon "make clean"!
+#     Even though the DOS/Win* filesystem matches both .s and .S the same,
+#     it will preserve the spelling of the filenames, and gcc itself does
+#     care about how the name is spelled on its command-line.
+ASRC = 
+
+
+# Optimization level, can be [0, 1, 2, 3, s]. 
+#     0 = turn off optimization. s = optimize for size.
+#     (Note: 3 is not always the best optimization level. See avr-libc FAQ.)
+OPT = s
+
+
+# Debugging format.
+#     Native formats for AVR-GCC's -g are dwarf-2 [default] or stabs.
+#     AVR Studio 4.10 requires dwarf-2.
+#     AVR [Extended] COFF format requires stabs, plus an avr-objcopy run.
+DEBUG = dwarf-2
+
+
+# List any extra directories to look for include files here.
+#     Each directory must be seperated by a space.
+#     Use forward slashes for directory separators.
+#     For a directory that has spaces, enclose it in quotes.
+EXTRAINCDIRS = 
+
+
+# Compiler flag to set the C Standard level.
+#     c89   = "ANSI" C
+#     gnu89 = c89 plus GCC extensions
+#     c99   = ISO C99 standard (not yet fully implemented)
+#     gnu99 = c99 plus GCC extensions
+CSTANDARD = -std=gnu99
+
+
+# Place -D or -U options here
+CDEFS = -DF_CPU=$(F_CPU)UL  
+
+# uncomment and adapt these line if you want different UART library buffer size
+#CDEFS += -DUART_RX_BUFFER_SIZE=128
+#CDEFS += -DUART_TX_BUFFER_SIZE=128
+
+
+# Place -I options here
+CINCS =
+
+
+
+#---------------- Compiler Options ----------------
+#  -g*:          generate debugging information
+#  -O*:          optimization level
+#  -f...:        tuning, see GCC manual and avr-libc documentation
+#  -Wall...:     warning level
+#  -Wa,...:      tell GCC to pass this to the assembler.
+#    -adhlns...: create assembler listing
+CFLAGS = -g$(DEBUG)
+CFLAGS += $(CDEFS) $(CINCS)
+CFLAGS += -O$(OPT)
+CFLAGS += -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums
+CFLAGS += -Wall -Wstrict-prototypes
+CFLAGS += -Wa,-adhlns=$(<:.c=.lst)
+CFLAGS += $(patsubst %,-I%,$(EXTRAINCDIRS))
+CFLAGS += $(CSTANDARD)
+
+
+#---------------- Assembler Options ----------------
+#  -Wa,...:   tell GCC to pass this to the assembler.
+#  -ahlms:    create listing
+#  -gstabs:   have the assembler create line number information; note that
+#             for use in COFF files, additional information about filenames
+#             and function names needs to be present in the assembler source
+#             files -- see avr-libc docs [FIXME: not yet described there]
+ASFLAGS = -Wa,-adhlns=$(<:.S=.lst),-gstabs 
+
+
+#---------------- Library Options ----------------
+# Minimalistic printf version
+PRINTF_LIB_MIN = -Wl,-u,vfprintf -lprintf_min
+
+# Floating point printf version (requires MATH_LIB = -lm below)
+PRINTF_LIB_FLOAT = -Wl,-u,vfprintf -lprintf_flt
+
+# If this is left blank, then it will use the Standard printf version.
+PRINTF_LIB = 
+#PRINTF_LIB = $(PRINTF_LIB_MIN)
+#PRINTF_LIB = $(PRINTF_LIB_FLOAT)
+
+
+# Minimalistic scanf version
+SCANF_LIB_MIN = -Wl,-u,vfscanf -lscanf_min
+
+# Floating point + %[ scanf version (requires MATH_LIB = -lm below)
+SCANF_LIB_FLOAT = -Wl,-u,vfscanf -lscanf_flt
+
+# If this is left blank, then it will use the Standard scanf version.
+SCANF_LIB = 
+#SCANF_LIB = $(SCANF_LIB_MIN)
+#SCANF_LIB = $(SCANF_LIB_FLOAT)
+
+
+MATH_LIB = -lm
+
+
+
+#---------------- External Memory Options ----------------
+
+# 64 KB of external RAM, starting after internal RAM (ATmega128!),
+# used for variables (.data/.bss) and heap (malloc()).
+#EXTMEMOPTS = -Wl,-Tdata=0x801100,--defsym=__heap_end=0x80ffff
+
+# 64 KB of external RAM, starting after internal RAM (ATmega128!),
+# only used for heap (malloc()).
+#EXTMEMOPTS = -Wl,--defsym=__heap_start=0x801100,--defsym=__heap_end=0x80ffff
+
+EXTMEMOPTS =
+
+
+
+#---------------- Linker Options ----------------
+#  -Wl,...:     tell GCC to pass this to linker.
+#    -Map:      create map file
+#    --cref:    add cross reference to  map file
+LDFLAGS = -Wl,-Map=$(TARGET).map,--cref
+LDFLAGS += $(EXTMEMOPTS)
+LDFLAGS += $(PRINTF_LIB) $(SCANF_LIB) $(MATH_LIB)
+
+
+
+#---------------- Programming Options (avrdude) ----------------
+
+# Programming hardware: alf avr910 avrisp bascom bsd 
+# dt006 pavr picoweb pony-stk200 sp12 stk200 stk500
+#
+# Type: avrdude -c ?
+# to get a full listing.
+#
+AVRDUDE_PROGRAMMER = arduino
+
+# com1 = serial port. Use lpt1 to connect to parallel port.
+AVRDUDE_PORT = /dev/tty.usb*    # programmer connected to serial device
+
+AVRDUDE_WRITE_FLASH = -U flash:w:$(TARGET).hex
+#AVRDUDE_WRITE_EEPROM = -U eeprom:w:$(TARGET).eep
+
+
+# Uncomment the following if you want avrdude's erase cycle counter.
+# Note that this counter needs to be initialized first using -Yn,
+# see avrdude manual.
+#AVRDUDE_ERASE_COUNTER = -y
+
+# Uncomment the following if you do /not/ wish a verification to be
+# performed after programming the device.
+#AVRDUDE_NO_VERIFY = -V
+
+# Increase verbosity level.  Please use this when submitting bug
+# reports about avrdude. See <http://savannah.nongnu.org/projects/avrdude> 
+# to submit bug reports.
+#AVRDUDE_VERBOSE = -v -v
+
+AVRDUDE_FLAGS = -p $(MCU) -P $(AVRDUDE_PORT) -c $(AVRDUDE_PROGRAMMER) -b 57600
+AVRDUDE_FLAGS += $(AVRDUDE_NO_VERIFY)
+AVRDUDE_FLAGS += $(AVRDUDE_VERBOSE)
+AVRDUDE_FLAGS += $(AVRDUDE_ERASE_COUNTER)
+
+
+
+#---------------- Debugging Options ----------------
+
+# For simulavr only - target MCU frequency.
+DEBUG_MFREQ = $(F_CPU)
+
+# Set the DEBUG_UI to either gdb or insight.
+# DEBUG_UI = gdb
+DEBUG_UI = insight
+
+# Set the debugging back-end to either avarice, simulavr.
+DEBUG_BACKEND = avarice
+#DEBUG_BACKEND = simulavr
+
+# GDB Init Filename.
+GDBINIT_FILE = __avr_gdbinit
+
+# When using avarice settings for the JTAG
+JTAG_DEV = /dev/com1
+
+# Debugging port used to communicate between GDB / avarice / simulavr.
+DEBUG_PORT = 4242
+
+# Debugging host used to communicate between GDB / avarice / simulavr, normally
+#     just set to localhost unless doing some sort of crazy debugging when 
+#     avarice is running on a different computer.
+DEBUG_HOST = localhost
+
+
+
+#============================================================================
+
+
+# Define programs and commands.
+SHELL = sh
+CC = avr-gcc
+OBJCOPY = avr-objcopy
+OBJDUMP = avr-objdump
+SIZE = avr-size
+NM = avr-nm
+AVRDUDE = avrdude
+REMOVE = rm -f
+COPY = cp
+WINSHELL = cmd
+
+
+# Define Messages
+# English
+MSG_ERRORS_NONE = Errors: none
+MSG_BEGIN = -------- begin --------
+MSG_END = --------  end  --------
+MSG_SIZE_BEFORE = Size before: 
+MSG_SIZE_AFTER = Size after:
+MSG_COFF = Converting to AVR COFF:
+MSG_EXTENDED_COFF = Converting to AVR Extended COFF:
+MSG_FLASH = Creating load file for Flash:
+MSG_EEPROM = Creating load file for EEPROM:
+MSG_EXTENDED_LISTING = Creating Extended Listing:
+MSG_SYMBOL_TABLE = Creating Symbol Table:
+MSG_LINKING = Linking:
+MSG_COMPILING = Compiling:
+MSG_ASSEMBLING = Assembling:
+MSG_CLEANING = Cleaning project:
+
+
+
+
+# Define all object files.
+OBJ = $(SRC:.c=.o) $(ASRC:.S=.o) 
+
+# Define all listing files.
+LST = $(SRC:.c=.lst) $(ASRC:.S=.lst) 
+
+
+# Compiler flags to generate dependency files.
+GENDEPFLAGS = -MD -MP -MF .dep/$(@F).d
+
+
+# Combine all necessary flags and optional flags.
+# Add target processor to flags.
+ALL_CFLAGS = -mmcu=$(MCU) -I. $(CFLAGS) $(GENDEPFLAGS)
+ALL_ASFLAGS = -mmcu=$(MCU) -I. -x assembler-with-cpp $(ASFLAGS)
+
+
+
+
+
+# Default target.
+all: begin gccversion sizebefore build sizeafter end
+
+build: elf hex eep lss sym
+
+elf: $(TARGET).elf
+hex: $(TARGET).hex
+eep: $(TARGET).eep
+lss: $(TARGET).lss 
+sym: $(TARGET).sym
+
+
+
+# Eye candy.
+# AVR Studio 3.x does not check make's exit code but relies on
+# the following magic strings to be generated by the compile job.
+begin:
+	@echo
+	@echo $(MSG_BEGIN)
+
+end:
+	@echo $(MSG_END)
+	@echo
+
+
+# Display size of file.
+HEXSIZE = $(SIZE) --target=$(FORMAT) $(TARGET).hex
+ELFSIZE = $(SIZE) -A $(TARGET).elf
+AVRMEM = avr-mem.sh $(TARGET).elf $(MCU)
+
+sizebefore:
+	@if test -f $(TARGET).elf; then echo; echo $(MSG_SIZE_BEFORE); $(ELFSIZE); \
+	$(AVRMEM) 2>/dev/null; echo; fi
+
+sizeafter:
+	@if test -f $(TARGET).elf; then echo; echo $(MSG_SIZE_AFTER); $(ELFSIZE); \
+	$(AVRMEM) 2>/dev/null; echo; fi
+
+
+
+# Display compiler version information.
+gccversion : 
+	@$(CC) --version
+
+
+
+# Program the device.  
+program: $(TARGET).hex $(TARGET).eep
+	$(AVRDUDE) $(AVRDUDE_FLAGS) $(AVRDUDE_WRITE_FLASH) $(AVRDUDE_WRITE_EEPROM)
+
+
+# Generate avr-gdb config/init file which does the following:
+#     define the reset signal, load the target file, connect to target, and set 
+#     a breakpoint at main().
+gdb-config: 
+	@$(REMOVE) $(GDBINIT_FILE)
+	@echo define reset >> $(GDBINIT_FILE)
+	@echo SIGNAL SIGHUP >> $(GDBINIT_FILE)
+	@echo end >> $(GDBINIT_FILE)
+	@echo file $(TARGET).elf >> $(GDBINIT_FILE)
+	@echo target remote $(DEBUG_HOST):$(DEBUG_PORT)  >> $(GDBINIT_FILE)
+ifeq ($(DEBUG_BACKEND),simulavr)
+	@echo load  >> $(GDBINIT_FILE)
+endif	
+	@echo break main >> $(GDBINIT_FILE)
+	
+debug: gdb-config $(TARGET).elf
+ifeq ($(DEBUG_BACKEND), avarice)
+	@echo Starting AVaRICE - Press enter when "waiting to connect" message displays.
+	@$(WINSHELL) /c start avarice --jtag $(JTAG_DEV) --erase --program --file \
+	$(TARGET).elf $(DEBUG_HOST):$(DEBUG_PORT)
+	@$(WINSHELL) /c pause
+	
+else
+	@$(WINSHELL) /c start simulavr --gdbserver --device $(MCU) --clock-freq \
+	$(DEBUG_MFREQ) --port $(DEBUG_PORT)
+endif
+	@$(WINSHELL) /c start avr-$(DEBUG_UI) --command=$(GDBINIT_FILE)
+	
+
+
+
+# Convert ELF to COFF for use in debugging / simulating in AVR Studio or VMLAB.
+COFFCONVERT=$(OBJCOPY) --debugging \
+--change-section-address .data-0x800000 \
+--change-section-address .bss-0x800000 \
+--change-section-address .noinit-0x800000 \
+--change-section-address .eeprom-0x810000 
+
+
+coff: $(TARGET).elf
+	@echo
+	@echo $(MSG_COFF) $(TARGET).cof
+	$(COFFCONVERT) -O coff-avr $< $(TARGET).cof
+
+
+extcoff: $(TARGET).elf
+	@echo
+	@echo $(MSG_EXTENDED_COFF) $(TARGET).cof
+	$(COFFCONVERT) -O coff-ext-avr $< $(TARGET).cof
+
+
+
+# Create final output files (.hex, .eep) from ELF output file.
+%.hex: %.elf
+	@echo
+	@echo $(MSG_FLASH) $@
+	$(OBJCOPY) -O $(FORMAT) -R .eeprom $< $@
+
+%.eep: %.elf
+	@echo
+	@echo $(MSG_EEPROM) $@
+	-$(OBJCOPY) -j .eeprom --set-section-flags=.eeprom="alloc,load" \
+	--change-section-lma .eeprom=0 -O $(FORMAT) $< $@
+
+# Create extended listing file from ELF output file.
+%.lss: %.elf
+	@echo
+	@echo $(MSG_EXTENDED_LISTING) $@
+	$(OBJDUMP) -h -S $< > $@
+
+# Create a symbol table from ELF output file.
+%.sym: %.elf
+	@echo
+	@echo $(MSG_SYMBOL_TABLE) $@
+	$(NM) -n $< > $@
+
+
+
+# Link: create ELF output file from object files.
+.SECONDARY : $(TARGET).elf
+.PRECIOUS : $(OBJ)
+%.elf: $(OBJ)
+	@echo
+	@echo $(MSG_LINKING) $@
+	$(CC) $(ALL_CFLAGS) $^ --output $@ $(LDFLAGS)
+
+
+# Compile: create object files from C source files.
+%.o : %.c
+	@echo
+	@echo $(MSG_COMPILING) $<
+	$(CC) -c $(ALL_CFLAGS) $< -o $@ 
+
+
+# Compile: create assembler files from C source files.
+%.s : %.c
+	$(CC) -S $(ALL_CFLAGS) $< -o $@
+
+
+# Assemble: create object files from assembler source files.
+%.o : %.S
+	@echo
+	@echo $(MSG_ASSEMBLING) $<
+	$(CC) -c $(ALL_ASFLAGS) $< -o $@
+
+# Create preprocessed source for use in sending a bug report.
+%.i : %.c
+	$(CC) -E -mmcu=$(MCU) -I. $(CFLAGS) $< -o $@ 
+
+
+# Target: clean project.
+clean: begin clean_list end
+
+clean_list :
+	@echo
+	@echo $(MSG_CLEANING)
+	$(REMOVE) $(TARGET).hex
+	$(REMOVE) $(TARGET).eep
+	$(REMOVE) $(TARGET).cof
+	$(REMOVE) $(TARGET).elf
+	$(REMOVE) $(TARGET).map
+	$(REMOVE) $(TARGET).sym
+	$(REMOVE) $(TARGET).lss
+	$(REMOVE) $(OBJ)
+	$(REMOVE) $(LST)
+	$(REMOVE) $(SRC:.c=.s)
+	$(REMOVE) $(SRC:.c=.d)
+	$(REMOVE) .dep/*
+
+
+
+# Include the dependency files.
+-include $(shell mkdir .dep 2>/dev/null) $(wildcard .dep/*)
+
+
+# Listing of phony targets.
+.PHONY : all begin finish end sizebefore sizeafter gccversion \
+build elf hex eep lss sym coff extcoff \
+clean clean_list program debug gdb-config
+

button_debounce_shift/main.c

@@ -0,0 +1,119 @@
+/*
+ * Button with debouncing. Based on the Arduino example but without
+ * Arduino libraries.
+ * 
+ * http://www.arduino.cc/en/Tutorial/Debounce
+ * 
+ * To compile and upload run: make clean; make; make program;
+ * 
+ * Copyright 2011 Mika Tuupola
+ *
+ * Licensed under the MIT license:
+ *   http://www.opensource.org/licenses/mit-license.php
+ *
+ */
+
+
+#ifndef F_CPU
+#define F_CPU 16000000UL
+#endif
+
+#include <stdlib.h>
+#include <avr/io.h>
+#include <stdio.h>
+#include <util/delay.h>
+#include <stdint.h>
+#include <avr/sfr_defs.h>
+
+#include "main.h"
+#include "uart.h"
+#include "timer.h"
+
+void init(void) {
+    
+    /* Make PORTD2 (Arduino digital 2) input by clearing bit in DDR */
+    DDRD &= ~(_BV(PORTD2));
+
+    /* In input mode, when pull-up is enabled, default state of pin becomes ’1′. So even if */
+    /* you don’t connect anything to pin and if you try to read it, it will read as 1. Now, */
+    /* when you externally drive that pin to zero(i.e. connect to ground / or pull-down),   */
+    /* only then it will be read as 0. */
+
+    /* Enable pullups by setting bits in PORT. Default state is now high. */
+    PORTD |= (_BV(PORTD2));
+    
+    /* Make PORTB5 (Arduino digital 13) an output by setting bit in DDR. */
+    DDRB |= _BV(PORTB5);
+    
+}
+
+uint8_t digital_read(int input_register, int pin) {
+    return bit_is_set(input_register, pin) != 0 ? 1 : 0;
+}
+
+/* You could use cbi ie &= ~ or sbi ie |= but this makes code more readable. */
+void digital_write(volatile uint8_t *data_port, uint8_t pin, uint8_t value) {
+    if (0 == value) {
+        *data_port &= ~(_BV(pin));
+    } else {
+        *data_port |= _BV(pin);
+    }
+}
+
+int main(void) {    
+    
+    init();
+    timer_init();
+    uart_init();
+    stdout = &uart_output;
+    stdin  = &uart_input;
+    
+    uint8_t current_reading;
+    uint8_t current_state    = 0;
+    uint8_t shift_register   = 0;
+    
+    /* Rest of the variables are used only for debugging output. */
+    uint8_t previous_reading = 0;
+    uint8_t previous_state   = 0;
+    uint64_t last_toggle_time;
+
+    while (1) {
+        
+        /* Shift the register towards the most significant bit. */
+        shift_register = shift_register << 1;
+        current_reading = digital_read(PIND, PIND2);
+        
+        /* Set least significant bit to current reading. */
+        if (1 == current_reading) {
+            shift_register |= _BV(0);
+        } else {
+            shift_register &= ~(_BV(0));
+        }
+        
+        /* Used only for debugging purposes. */
+        if (current_reading != previous_reading) {
+            /* Note the time in millis of last change of button state. */
+            last_toggle_time = timer_millis();
+            printf("- Reading toggled %d (%d)\n", current_reading, last_toggle_time);
+        }
+        
+        /* If shift register is 0b00000000 or 0b11111111 switch has been */
+        /* high or low long enough to assume reading is not noise.       */
+        if (0 == shift_register) {
+            current_state = 0;
+        } else if (255 == shift_register){
+            current_state = 1;
+        }
+        
+        /* Used only for debugging purposes. */
+        if (current_state != previous_state) {
+            printf("+ State toggled %d (%d)\n", current_state, last_toggle_time);
+            previous_state = current_state;
+        }
+        
+        previous_reading = current_reading;
+        
+    }
+    return 0;
+  
+}

button_debounce_shift/main.h

@@ -0,0 +1,2 @@
+static void uart_init(void);
+static void init(void);

button_debounce_shift/timer.c

@@ -0,0 +1,63 @@
+/*
+ * Low resolution implementation of timer using a 8 bit clock with prescaler, 
+ * etc.  Clicks approximately every millisecond.  Microseconds are not available, 
+ * and any queries to the function will just return milliseconds * 1000.
+ * You can use this file when you don't need high resolution timing, and don't care
+ * about slight clock drift, inaccuracy, etc.  For timing most human-related activities,
+ * though, it should be more than sufficient.
+ */
+#include "timer.h"
+
+static volatile uint64_t _timer_millis;
+
+/*
+ * Initializes the timer, and resets the timer count to 0.  Sets up the ISRs 
+ * linked with timer0.
+ */
+void timer_init(){
+	//Set up the timer to run at F_CPU / 256, in normal mode (we reset TCNT0 in the ISR)
+	TCCR0A = 0x0;
+	TCCR0B |= _BV(CS02);
+	
+	//Set compare value to be F_CPU / 1000 -- fire interrupt every millisecond
+	OCR0A = F_CPU / 256 / 1000;
+	
+	//Enable compare interrupt
+	TIMSK0 = _BV(OCIE0A);
+
+	//Reset count variables
+	_timer_millis = 0;
+	
+	//Enable interrupts if the NO_INTERRUPT_ENABLE define is not set.  If it is, you need to call sei() elsewhere.
+#ifndef NO_INTERRUPT_ENABLE
+	sei();
+#endif
+	
+	DDRB = 0xFF;
+}
+
+/*
+ * Returns the number of milliseconds which have elapsed since the 
+ * last time timer_init() was called.  Overflows after about 49 days.
+ */
+uint64_t timer_millis(){
+	return _timer_millis;
+}
+
+/*
+ * Returns the number of microseconds which have elapsed since the 
+ * last time timer_init() was called.  Overflows after about 71 minutes.
+ */
+uint64_t timer_micros(){
+	return (_timer_millis * 1000);
+}
+
+
+/* 
+ * The ISR for timer0 overflow.  Increment the _timer_count here, and do the calculcations
+ * to increment _timer_millis as needed.
+ */
+ISR(TIMER0_COMPA_vect){
+	TCNT0 = 0;
+	_timer_millis++;
+}

button_debounce_shift/timer.h

@@ -0,0 +1,25 @@
+#ifndef TIMER_H
+#define TIMER_H
+
+#include <avr/io.h>
+#include <avr/interrupt.h>
+
+/*
+ * Initializes the timer, and resets the timer count to 0.  Sets up the ISRs 
+ * linked with timer1.
+ */
+void timer_init();
+
+/*
+ * Returns the number of milliseconds which have elapsed since the 
+ * last time timer_init() was called.  Overflows after about 49 days.
+ */
+uint64_t timer_millis();
+
+/*
+ * Returns the number of microseconds which have elapsed since the 
+ * last time timer_init() was called.  Overflows after about 71 minutes.
+ */
+uint64_t timer_micros();
+
+#endif

button_debounce_shift/uart.h

@@ -0,0 +1,12 @@
+int uart_putchar(char c, FILE *stream);
+int uart_getchar(FILE *stream);
+
+void uart_init(void);
+
+struct rx_ring;
+struct tx_ring;
+
+/* http://www.ermicro.com/blog/?p=325 */
+
+FILE uart_output = FDEV_SETUP_STREAM(uart_putchar, NULL, _FDEV_SETUP_WRITE);
+FILE uart_input = FDEV_SETUP_STREAM(NULL, uart_getchar, _FDEV_SETUP_READ);

button_debounce_shift/uart_async.c

@@ -0,0 +1,102 @@
+/* Based on Atmel Application Note AVR 306 */
+
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <stdio.h>
+
+#ifndef BAUD
+#define BAUD 9600
+#endif
+#include <util/setbaud.h>
+
+#ifndef UART_RX_BUFFER_SIZE
+#define UART_RX_BUFFER_SIZE 32
+#endif
+
+#ifndef UART_TX_BUFFER_SIZE
+#define UART_TX_BUFFER_SIZE 256
+#endif
+
+struct tx_ring {
+    int buffer[UART_TX_BUFFER_SIZE];
+    int start;
+    int end;
+};
+
+struct rx_ring {
+    int buffer[UART_RX_BUFFER_SIZE];
+    int start;
+    int end;
+};
+
+static struct tx_ring tx_buffer;
+static struct rx_ring rx_buffer;
+
+/* http://www.cs.mun.ca/~rod/Winter2007/4723/notes/serial/serial.html */
+
+void uart_init(void) {
+    
+    tx_buffer.start = 0;
+    tx_buffer.end   = 0;
+
+    rx_buffer.start = 0;
+    rx_buffer.end   = 0;
+    
+    UBRR0H = UBRRH_VALUE;
+    UBRR0L = UBRRL_VALUE;
+
+    UCSR0C = _BV(UCSZ01) | _BV(UCSZ00); /* 8-bit data */ 
+    UCSR0B = _BV(RXEN0) | _BV(TXEN0);   /* Enable RX and TX */  
+    
+    sei();  
+}
+
+int uart_putchar(char c, FILE *stream) {
+    if (c == '\n') {
+        uart_putchar('\r', stream);
+    }
+    
+    int write_pointer = (tx_buffer.end + 1) % UART_TX_BUFFER_SIZE;
+    
+    if (write_pointer != tx_buffer.start){
+        tx_buffer.buffer[tx_buffer.end] = c;
+        tx_buffer.end = write_pointer;
+        
+        /* Data available. Enable the transmit interrupt for serial port 0. */
+        UCSR0B |= _BV(UDRIE0);  
+    }
+    
+    return 0;
+}
+
+int uart_getchar(FILE *stream) {
+    int read_pointer = (rx_buffer.start + 1) % UART_RX_BUFFER_SIZE;
+    
+    rx_buffer.start = read_pointer;
+    return rx_buffer.buffer[read_pointer];
+}
+
+ISR(USART_RX_vect) {
+    int write_pointer = (rx_buffer.end + 1) % UART_RX_BUFFER_SIZE;
+
+    /* Add next byte to ringbuffer if it has space available. */
+    if (write_pointer != rx_buffer.start){
+        rx_buffer.buffer[rx_buffer.end] = UDR0;
+        rx_buffer.end = write_pointer;
+    }
+}
+
+ISR(USART_UDRE_vect){
+    int read_pointer = (tx_buffer.start + 1) % UART_TX_BUFFER_SIZE;
+    
+    /* Transmit next byte if data available in ringbuffer. */
+    if (read_pointer != tx_buffer.end) {
+        UDR0 = tx_buffer.buffer[read_pointer];
+        tx_buffer.start = read_pointer;
+    } else {
+        /* Nothing to send. Disable the transmit interrupt for serial port 0. */
+        UCSR0B &= ~_BV(UDRIE0);
+    }
+}
+
+