Initial prototype

This patch adds a skeleton of AVR code for a "simulator" target (atmega2560)
and for the real intended hardware target (atmega32u4). The simulator target
is one that is supported by the QEMU AVR emulator, while the 32u4 is currently
not.

10 files changed, 347 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..4b523e3
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+*.hex
+*.o
+*.elf
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..879452f
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,54 @@
+CC ?= avr-gcc
+OBJCOPY ?= avr-objcopy
+AVRDUDE ?= avrdude
+QEMU_AVR ?= qemu-system-avr
+
+MCU ?= atmega32u4
+SIM_MCU ?= atmega2560
+CFLAGS += -DF_CPU=16000000UL -mmcu=$(MCU) -O3
+SIM_CFLAGS += -DF_CPU=16000000UL -mmcu=$(SIM_MCU) -g3 -gdwarf-2
+
+$(shell mkdir -p build/{real,sim})
+
+all: build/altimeter_sim.elf build/altimeter.hex
+
+emu: build/altimeter_sim.elf
+	$(QEMU_AVR) -s -S -nographic -machine mega2560 -bios $<
+
+flash: build/altimeter.hex
+	$(AVRDUDE) -F -V -c avr109 -p $(MCU) -P $(PORT) -b 115200 -U flash:w:$<
+
+clean:
+	rm -rf build/
+
+build/altimeter.elf: \
+	build/real/barometer_sim.o \
+	build/real/display_sim.o \
+	build/real/altimeter.o \
+	build/real/util.o
+	$(CC) -o $@ $^ $(CFLAGS)
+
+build/altimeter_sim.elf: \
+	build/sim/barometer_sim.o \
+	build/sim/display_sim.o \
+	build/sim/altimeter.o \
+	build/sim/util.o
+	$(CC) -o $@ $^ $(SIM_CFLAGS)
+
+include config.mk
+
+
+build/sim/%.o: %.c
+	$(CC) -c -o $@ $^ $(SIM_CFLAGS)
+
+build/real/%.o: %.c
+	$(CC) -c -o $@ $^ $(CFLAGS)
+
+build/%.hex: build/%.elf
+	$(OBJCOPY) -O ihex -R .eeprom $< $@
+
+build/%.elf:
+	$(CC) -o $@ $^ $(CFLAGS)
+
+
+.PHONY: all emu flash clean
diff --git a/altimeter.c b/altimeter.c
new file mode 100644
index 0000000..2aef956
--- /dev/null
+++ b/altimeter.c
@@ -0,0 +1,100 @@
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <avr/sleep.h>
+#include <avr/interrupt.h>
+
+#include "barometer.h"
+#include "display.h"
+#include "util.h"
+
+/* ISR for collecting and displaying pressure, altitude data etc */
+ISR(TIMER1_COMPA_vect)
+{
+	PORTD ^= 1 << 5;
+	int tcnt1_start = TCNT1;
+	static volatile float setting = 1040.21; /* FIXME volatile for gdb hacks */
+	static float last_height = 0;
+	float pressure = 0;
+	float height_m = 0;
+	float rate_m_s;
+	char rate_sym;
+	pressure = barometer_read();
+	height_m = pressure_to_metres_asl(pressure, setting);
+	rate_m_s = height_m - last_height;
+	last_height = height_m;
+
+	if (rate_m_s < 0) {
+		rate_sym = C_DESC;
+	} else if (rate_m_s == 0) {
+		rate_sym = C_IDLE;
+	} else {
+		rate_sym = C_ASC;
+	}
+
+	char line[LCD_WIDTH+1];
+	/* line 1 */
+	int alt_m_int;
+	float alt_m_float;
+	split_float(height_m, &alt_m_int, &alt_m_float);
+	snprintf(line, sizeof(line), "%d.%d m %c%d m/s", alt_m_int, (int)(round(alt_m_float*10)), rate_sym, abs(rate_m_s));
+	blank_to_eol(line, sizeof(line));
+	display_set_cursor(0, 0);
+	display_write(line);
+
+
+	/* line 2 */
+	int pressure_hpa_int;
+	float pressure_hpa_float;
+	split_float(pressure, &pressure_hpa_int, &pressure_hpa_float);
+	snprintf(line, sizeof(line), "%d.%d hPa", pressure_hpa_int, (int)(round(pressure_hpa_float*100)));
+	blank_to_eol(line, sizeof(line));
+	display_set_cursor(0, 1);
+	display_write(line);
+
+	/* line 3 */
+	int setting_hpa_int;
+	float setting_hpa_float;
+	split_float(setting, &setting_hpa_int, &setting_hpa_float);
+	snprintf(line, sizeof(line), "SET %d.%d hPa", setting_hpa_int, (int)(round(setting_hpa_float*100)));
+	blank_to_eol(line, sizeof(line));
+	display_set_cursor(0, 2);
+	display_write(line);
+
+	int tcnt1_end = TCNT1;
+	/* line 4 */
+	snprintf(line, sizeof(line), "TCNT1 delta %u", tcnt1_end - tcnt1_start);
+	blank_to_eol(line, sizeof(line));
+	display_set_cursor(0, 3);
+	display_write(line);
+	return;
+}
+
+int main(void)
+{
+	/* Initialise display before enabling interrupts */
+	display_init();
+	display_clear();
+
+	DDRB |= 1 << 0;
+	DDRD |= 1 << 5;
+
+	/* Initialise timers for /1024 prescaler, 1 Hz comparator val */
+	TCCR1B |= (1 << CS10) | (1 << CS12) | (1 << WGM12);
+	TIMSK1 |= (1 << OCIE1A);
+	OCR1A = 15624;
+
+#ifdef USBCON
+	/* Disable USB controller if one is present - this spams (latches?) USB_GEN
+	 * interrupt which we're not handling for now */
+	USBCON &= ~(1 << USBE);
+#endif
+
+	sei();
+	while(1) {
+		set_sleep_mode(SLEEP_MODE_IDLE);
+		sleep_mode();
+	}
+}
diff --git a/barometer.h b/barometer.h
new file mode 100644
index 0000000..8277665
--- /dev/null
+++ b/barometer.h
@@ -0,0 +1,3 @@
+#pragma once
+
+float barometer_read(void);
diff --git a/barometer_sim.c b/barometer_sim.c
new file mode 100644
index 0000000..f2e9eac
--- /dev/null
+++ b/barometer_sim.c
@@ -0,0 +1,22 @@
+/* Dummy pressures to return in sequence, each call to barometer_read */
+static const float pressures[] = {
+	1019.5,
+	1019.45,
+	1019.41,
+	1019.33,
+	1019.2,
+	1019.0,
+	1018.99,
+	1018.91,
+	1018.88,
+	1018.86,
+	1018.83,
+	1018.82,
+};
+
+float barometer_read(void)
+{
+	static int i = 0;
+	i %= sizeof(pressures)/sizeof(pressures[0]);
+	return pressures[i++];
+}
diff --git a/config.mk b/config.mk
new file mode 100644
index 0000000..7eb0c2e
--- /dev/null
+++ b/config.mk
@@ -0,0 +1 @@
+CC = avr-gcc
diff --git a/display.h b/display.h
new file mode 100644
index 0000000..771323c
--- /dev/null
+++ b/display.h
@@ -0,0 +1,14 @@
+#pragma once
+
+#define LCD_WIDTH (20)
+#define LCD_HEIGHT (4)
+
+#define C_BAT_LOW (1)
+#define C_DESC    (2)
+#define C_IDLE    (3)
+#define C_ASC     (4)
+
+void display_clear(void);
+void display_init(void);
+void display_write(const char *text);
+void display_set_cursor(int x, int y);
diff --git a/display_sim.c b/display_sim.c
new file mode 100644
index 0000000..b17979f
--- /dev/null
+++ b/display_sim.c
@@ -0,0 +1,118 @@
+#include <stdio.h>
+#include <avr/io.h>
+
+#define BAUD 57600
+#include <util/setbaud.h>
+
+#include "display.h"
+
+/* WIDTH+1 for string terminator */
+static char display[LCD_HEIGHT][LCD_WIDTH+1];
+static int cursor_x;
+static int cursor_y;
+
+/* Slightly icky hack to use first avaialable USART */
+#ifdef UDR0
+#  define UBRRx  UBRR0
+#  define UCSRxA UCSR0A
+#  define UCSRxB UCSR0B
+#  define UCSRxC UCSR0C
+#  define UCSZx0 UCSZ00
+#  define UCSZx1 UCSZ01
+#  define RXENx  RXEN0
+#  define TXENx  TXEN0
+#  define UDREx  UDRE0
+#  define UDRx   UDR0
+#  define U2Xx   U2X0
+#else
+#  define UBRRx  UBRR1
+#  define UCSRxA UCSR1A
+#  define UCSRxB UCSR1B
+#  define UCSRxC UCSR1C
+#  define UCSZx0 UCSZ10
+#  define UCSZx1 UCSZ11
+#  define RXENx  RXEN1
+#  define TXENx  TXEN1
+#  define UDREx  UDRE1
+#  define UDRx   UDR1
+#  define U2Xx   U2X1
+#endif
+
+static void uart_init(void)
+{
+	UBRRx = UBRR_VALUE;
+#if USE_2X
+	UCSRxA |= (1 << U2Xx);
+#else
+	UCSRxA &= ~(1 << U2Xx);
+#endif
+    UCSRxB = _BV(RXENx) | _BV(TXENx);
+    UCSRxC = _BV(UCSZx1) | _BV(UCSZx0);
+}
+
+static int uart_putc(char c, FILE *unused)
+{
+	UDRx = c;
+	loop_until_bit_is_set(UCSRxA, UDREx);
+	return 1;
+}
+
+/* uart_out is plopped on stdout so that prints go to it by default */
+static FILE uart_out = FDEV_SETUP_STREAM(uart_putc, NULL, _FDEV_SETUP_WRITE);
+
+/* internal function to dump the display contents to stdout, since there
+ * is no background thread for doing this constantly */
+void display_display(void)
+{
+	int x = 0;
+	int y = 0;
+	printf("\033[6A"); // hack: raw ANSI escape sequence to move up 6
+	printf(",--------------------.\n");
+	for (y = 0; y < LCD_HEIGHT; y++) {
+		printf("|%s|\n", display[y]);
+	}
+	printf("`--------------------'\n");
+}
+
+void display_clear(void)
+{
+	int x = 0;
+	int y = 0;
+	for (y = 0; y < LCD_HEIGHT; y++) {
+		for (x = 0; x < LCD_WIDTH; x++) {
+			display[y][x] = ' ';
+		}
+		display[y][x] = '\0';
+	}
+
+	display_display();
+}
+
+void display_init(void)
+{
+	uart_init();
+	/* FIXME hack: stdout not guaranteed to be assignable */
+	stdout = &uart_out;
+	display_clear();
+	cursor_x = cursor_y = 0;
+}
+
+void display_write(const char *text)
+{
+	size_t text_x = 0;
+	char c = '\0';
+	while (cursor_x < LCD_WIDTH && *text) {
+		c = *(text++);
+		/* 0-7 are custom chars in CGRAM on real LCD */
+		if (c < 8)
+			c = '_';
+		display[cursor_y][cursor_x++] = c;
+	}
+	display_display();
+}
+
+void display_set_cursor(int x, int y)
+{
+	cursor_x = x;
+	cursor_y = y;
+}
diff --git a/util.c b/util.c
new file mode 100644
index 0000000..794eea7
--- /dev/null
+++ b/util.c
@@ -0,0 +1,25 @@
+#include <math.h>
+#include <string.h>
+
+#include "util.h"
+
+float pressure_to_metres_asl(float real, float setting)
+{
+	return 44330.f*(1.f-pow(real/setting, 1/5.255));
+}
+
+void blank_to_eol(char *line, size_t len)
+{
+	size_t i = 0;
+	for (i = strlen(line); i < len - 1; i++) {
+		line[i] = ' ';
+	}
+	line[i] = '\0';
+}
+
+void split_float(float input, int *integer_part, float *float_part)
+{
+	*integer_part = (int)input;
+	*float_part = fabs(input - *integer_part);
+}
+
diff --git a/util.h b/util.h
new file mode 100644
index 0000000..49812b9
--- /dev/null
+++ b/util.h
@@ -0,0 +1,7 @@
+#pragma once
+
+#include <stddef.h>
+
+float pressure_to_metres_asl(float real, float setting);
+void blank_to_eol(char *line, size_t len);
+void split_float(float input, int *integer_part, float *float_part);