WIP: ADC skeleton code. Minimal SPI comms OK.

Makefile

@@ -25,10 +25,10 @@ clean:
 	rm -f $(TARGET).elf *.o *.hex
 
 %.o: %.c
-	$(GCC_BIN) -c $(C_FLAGS) $< -o $@
+	$(GCC_BIN) -c $(C_FLAGS) *.c
 
 $(TARGET).elf: $(TARGET).o
-	$(GCC_BIN) $(LD_FLAGS) $(TARGET).o -o $(TARGET).elf
+	$(GCC_BIN) $(LD_FLAGS) *.o -o $(TARGET).elf
 
 $(TARGET).hex: $(TARGET).elf
 	$(OBJCOPY_BIN) $(OBJCOPY_FLAGS) $(TARGET).elf $(TARGET).hex

ads8698.c

+/**
+ * This file includes functions for interacting with an ADC
+ *
+ * Written for: TI ADS8698 8-channel ADC
+ *
+ * Connections:
+ *    Function | ADC Pin     | AVR Port   | Pin # on DIP Atmega328P
+ *   ----------+-------------+------------+-------------------------
+ *    Data In  |  1 (SDI)    | PB3 (MOSI) | 17
+ *    Reset    |  2 (RST)    | PC0        | 23
+ *    Data Out | 36 (SDO)    | PB4 (MISO) | 18
+ *    Clock    | 37 (SCLK)   | PB5 (SCK)  | 19
+ *    Chip Sel.| 38 (CS)     | PC1        | 24
+ */
+
+#include <avr/io.h>
+#include <util/delay.h>
+
+#include "include/spi.h"
+#include "include/ads8698.h"
+
+/* Initialize the ADC. */
+void ADS8698_init(void) {
+
+    // Start SPI.
+    SPI_init();
+
+    // Set RST and CS as outputs.
+    DDRC |= (1<<DDC0) | (1<<DDC1);
+
+    // Pull RST and CS high.
+    PORTC |= _BV(PORTC0);
+    PORTC |= _BV(PORTC1);
+
+    // Reset the ADC.
+    ADS8698_reset();
+
+    // Start measurements
+    ADS8698_send_command(ADS8698_RESET);
+    SPI_transmit('H');
+    SPI_transmit('e');
+    SPI_transmit('l');
+    SPI_transmit('l');
+    SPI_transmit('o');
+    SPI_transmit('!');
+}
+
+/* Set the input range on the ADC. */
+void ADS8698_set_range(ADS8698_range range) {
+    // TODO
+    return;
+}
+
+/* Write to a register on the ADC. */
+void ADS8698_write_register(uint8_t address, uint8_t data) {
+    // TODO
+    return;
+}
+
+/* Send a command to the ADC. */
+void ADS8698_send_command(ADS8698_command command) {
+    // TODO
+    return;
+}
+
+/* Reset the ADC.
+ *
+ * Pull RST low for 70ns (instructions: 40-100ns).
+ * See datasheet section 8.4.1.1.6.
+ */
+void ADS8698_reset(void) {
+    PORTC &= ~_BV(PORTC0);
+    _delay_us(0.47);
+    PORTC |= _BV(PORTC0);
+}

blink.c

-#include <avr/io.h>
-#include <util/delay.h>
-
-#define STROBE_DURATION_MS 20
-
-/* This file is just placeholder stuff. It has nothing to do with testing. */
-
-void delay(int duration) {
-    duration = duration / 10;
-    while (duration--) {
-        _delay_ms(10);
-    }
-}
-
-void blink_once(int duration) {
-        /* Output High */
-        PORTB |= _BV(PORTB5);
-
-        /* Wait */
-        delay(duration);
-
-        /* Output Low */
-        PORTB &= ~_BV(PORTB5);
-}
-
-void strobe_pulse() {
-    /* Blinking pattern. Looks neat. */
-    for (int j = 5; j < 10; j++) {
-        for (int i = 1; i < j; i++) {
-            blink_once(STROBE_DURATION_MS * i);
-            delay(STROBE_DURATION_MS * i);
-        }
-        for (int i = j; i > 0; i--) {
-            blink_once(STROBE_DURATION_MS * i);
-            delay(STROBE_DURATION_MS * i);
-        }
-    }
-}

include/ads8698.h

+/**
+ * This file includes functions for interacting with an ADC
+ *
+ * Written for: TI ADS8698 8-channel ADC
+ *
+ * Connections:
+ *    Function | ADC Pin     | AVR Port   | Pin # on DIP Atmega328P
+ *   ----------+-------------+------------+-------------------------
+ *    Data In  |  1 (SDI)    | PB3 (MOSI) | 17
+ *    Reset    |  2 (RST)    | PC0        | 23
+ *    Data Out | 36 (SDO)    | PB4 (MISO) | 18
+ *    Clock    | 37 (SCLK)   | PB5 (SCK)  | 19
+ *    Chip Sel.| 38 (CS)     | PC1        | 24
+ */
+
+
+/* ADC Commands.
+ *
+ * See datasheet section 8.5.1.
+ */
+typedef enum {
+    ADS8698_NO_OP       = 0x00,  // Continue operating in previous mode.
+    ADS8698_STANDBY     = 0x82,  // Enter standby mode.
+    ADS8698_POWER_DOWN  = 0x83,  // Power down.
+    ADS8698_RESET       = 0x85,  // Reset.
+    ADS8698_AUTO_RESET  = 0xA0,  // Reset and enter auto-scan mode.
+    ADS8698_MANUAL_CH0  = 0xC0,  // Select channel 0 input.
+    ADS8698_MANUAL_CH1  = 0xC4,  // Select channel 1 input.
+    ADS8698_MANUAL_CH2  = 0xC8,  // Select channel 2 input.
+    ADS8698_MANUAL_CH3  = 0xCC,  // Select channel 3 input.
+    ADS8698_MANUAL_CH4  = 0xD0,  // Select channel 4 input.
+    ADS8698_MANUAL_CH5  = 0xD4,  // Select channel 5 input.
+    ADS8698_MANUAL_CH6  = 0xD8,  // Select channel 6 input.
+    ADS8698_MANUAL_CH7  = 0xDC,  // Select channel 7 input.
+    ADS8698_MANUAL_AUX  = 0xE0,  // Select aux input.
+} ADS8698_command;
+
+
+/* ADC Input Ranges.
+ *
+ * See datasheet section 8.5.2.3.3.
+ */
+typedef enum {
+    ADS8698_RANGE_BIPOLAR_2_5X   = 0x00,  // 0 +/- 2.5 x Vref
+    ADS8698_RANGE_BIPOLAR_1_25X  = 0x01,  // 0 +/- 1.25 x Vref
+    ADS8698_RANGE_BIPOLAR_0_625X = 0x02,  // 0 +/- 0.625 x Vref
+    ADS8698_RANGE_UNIPOLAR_2_5X  = 0x05,  // 0 + 2.5 x Vref
+    ADS8698_RANGE_UNIPOLAR_1_25X = 0x0    // 0 + 1.25 x Vref
+} ADS8698_range;
+
+
+/* Initialize the ADC. */
+void ADS8698_init(void);
+
+/* Set the input range on the ADC. */
+void ADS8698_set_range(ADS8698_range range);
+
+/* Send a command to the ADC. */
+void ADS8698_send_command(ADS8698_command command);
+
+/* Reset the ADC. */
+void ADS8698_reset(void);

include/measure.h

+/**
+ * This file includes functions for measuring electrical resistance.
+ */
+
+typedef struct Measurements Measurements;
+
+struct Measurements {
+    double value1, value2, value3, value4, value5, value6, value7, value8;
+};
+
+
+/* Prepare for measuring resistance. */
+void Measure_init(void);
+
+/* Acquire resistance measurements. */
+struct Measurements measure(void);

include/spi.h

+/**
+ * Logic for using SPI to communicate between the AVR and other devices.
+ */
+
+/* Initialize the microcontroller's SPI interface. */
+void SPI_init(void);
+
+/* Send a byte over the SPI interface. */
+void SPI_transmit(char data);
+
+/* Receive a byte from the SPI interface. */
+char SPI_receive(void);

main.c

-#include "blink.c"
+#include "include/measure.h"
 
+/* Start-up procedure */
 void init() {
-    /* Make Pin 5 of PORTB an output. */
-    DDRB |= _BV(DDB5);
+    /* Activate display. */
+    // TODO
+
+    /* Prepare ADC for measurements. */
+    Measure_init();
 }
 
+/* Main code; will repeat forever */
 void loop() {
-    /* Strobe forever */
-    strobe_pulse();
+    /* Measure resistance. */
+    // TODO
+    Measure_init();
+
+    /* Update display. */
+    // TODO
 }
 
 int main(void) {

measure.c

+/**
+ * This file includes functions for measuring electrical resistance.
+ */
+
+#include <avr/io.h>
+#include <util/delay.h>
+
+#include "include/spi.h"
+#include "include/ads8698.h"
+#include "include/measure.h"
+
+
+
+/* Acquire resistance measurements. */
+struct Measurements measure() {
+    /* Do the stuff. */
+    // TODO
+    return (Measurements) {1, 1, 1, 1, 1, 1, 1, 1};
+}
+
+
+/* Prepare for measuring resistance. */
+void Measure_init(void) {
+    ADS8698_init();
+    _delay_us(100);
+    // int sample_count = 2048; // TODO: what is this
+    // ADS8698_config(&sample_buffer, sample_count, ADS8698_CHANNEL_0, INPUT_RANGE_UNIPOLAR_1_25X_VREF);
+}

spi.c

+/**
+ * Logic for using SPI to communicate between the AVR and other devices.
+ */
+
+#include <avr/io.h>
+
+#include "include/spi.h"
+
+/* Initialize the microcontroller's SPI interface. */
+void SPI_init(void) {
+    // Set MOSI, SCK, and SS as outputs
+    DDRB = (1<<DDB3) | (1<<DDB5) | (1<<DDB2);
+
+    // Enable SPI, become master, set clock rate to CPU clock / 16.
+    SPCR = (1<<SPE) | (1<<MSTR);
+}
+
+/* Send a byte over the SPI interface. */
+void SPI_transmit(char data) {
+    // Put the data in the SPI Data Register.
+    SPDR = data;
+
+    // Wait for transmission to complete.
+    while(!(SPSR & (1<<SPIF)))
+        ;
+}
+
+/* Receive a byte from the SPI interface. */
+char SPI_receive(void) {
+    // Wait for reception to complete.
+    while (!(SPSR & (1<<SPIF)))
+        ;
+
+    // Return received value from data register.
+    return SPDR;
+}