edgar-bonet · June 21, 2017 20:03
diff --git a/dual-scope.c b/dual-scope.c
 /*
 * dual-scope.c: Dual channel Arduino/AVR oscilloscope.
 *
 * This program alternatively samples analog inputs 0 and 1, with an
 * overall sampling rate of about 9615 samp/s (one sample every 104 us),
 * i.e. 4808 samp/s per channel. The samples are output as 8-bit binary
 * through the serial port at 115200/8N1. A fixed 16-byte ASCII prologue
 * is sent at program startup, before the actual binary data, for
 * synchronization purposes. The first byte sent after the prologue is a
 * sample from channel 0.
 *
 * Program internals: The analog-to-digital converter is set to "free
 * running mode". The ADC ISR transfers the samples through the serial
 * port and switches the ADC multiplexer in order to sample both
 * channels.
 *
 * Target platform: This program is intended for an Arduino Uno, but it
 * does not use the Arduino libraries. It can be compiled either as a
 * .ino "sketch" or as a plain C file. It is likely to work on most
 * ATmega microcontrollers having an ADC and clocked at 16 MHz.
 *
 * Copyright (c) 2017 Edgar Bonet Orozco.
 * Released under the terms of the MIT license:
 * https://opensource.org/licenses/MIT
 */

 #include <avr/io.h>
 #include <avr/interrupt.h>
 #include <avr/sleep.h>
 #include <util/delay.h>

 #define BAUD     115200    // serial port baud rate
 #define BAUD_TOL      3    // increase the baud rate tolerance to 3%
 #include <util/setbaud.h>  // compute USE_2X and UBRR_VALUE

 #define PROLOGUE "== STARTING ==\r\n"

 // ADC interrupt service routine.
 ISR(ADC_vect)
 {
    // Output the 8-bit ADC reading through the serial port.
    UDR0 = ADCH;

    // Switch between ADC channels 0 and 1.
    ADMUX ^= _BV(MUX0);
 }

 int main(void)
 {
    // Configure the serial port.
    UCSR0A = USE_2X << U2X0;  // double speed if needed
    UCSR0B = _BV(TXEN0);      // enable only the transmitter
    UCSR0C = _BV(UCSZ00)      // character size = 8 bits
           | _BV(UCSZ01);     // ...ditto
    UBRR0  = UBRR_VALUE;      // set baud rate

    // Send the prologue.
    for (const char *p = PROLOGUE; *p; p++) {
        UDR0 = *p;                             // output
        loop_until_bit_is_set(UCSR0A, UDRE0);  // flush
    }

    // Configure the ADC in "free running mode".
    DIDR0  = _BV(ADC0D)   // disable the digital inputs ADC0...
           | _BV(ADC1D);  // ...and ADC1
    ADMUX  = _BV(REFS0)   // voltage reference = AVCC
           | _BV(ADLAR)   // left adjust result
           | 0;           // initial input channel = ADC0
    ADCSRB = 0;           // auto trigger source = self
    ADCSRA = _BV(ADEN)    // enable ADC
           | _BV(ADSC)    // start first conversion
           | _BV(ADATE)   // enable auto trigger
           | _BV(ADIF)    // clear interrupt flag
           | _BV(ADIE)    // enable interrupt
           | 7;           // prescaler = 128
    _delay_us(9);         // let the conversion start
    ADMUX  |= _BV(MUX0);  // first channel switch

    // Sleep while waiting for interrupts.
    sei();
    sleep_enable();
    for (;;)
        sleep_cpu();
 }
	/*
	* dual-scope.c: Dual channel Arduino/AVR oscilloscope.
	*
	* This program alternatively samples analog inputs 0 and 1, with an
	* overall sampling rate of about 9615 samp/s (one sample every 104 us),
	* i.e. 4808 samp/s per channel. The samples are output as 8-bit binary
	* through the serial port at 115200/8N1. A fixed 16-byte ASCII prologue
	* is sent at program startup, before the actual binary data, for
	* synchronization purposes. The first byte sent after the prologue is a
	* sample from channel 0.
	*
	* Program internals: The analog-to-digital converter is set to "free
	* running mode". The ADC ISR transfers the samples through the serial
	* port and switches the ADC multiplexer in order to sample both
	* channels.
	*
	* Target platform: This program is intended for an Arduino Uno, but it
	* does not use the Arduino libraries. It can be compiled either as a
	* .ino "sketch" or as a plain C file. It is likely to work on most
	* ATmega microcontrollers having an ADC and clocked at 16 MHz.
	*
	* Copyright (c) 2017 Edgar Bonet Orozco.
	* Released under the terms of the MIT license:
	* https://opensource.org/licenses/MIT
	*/

	#include <avr/io.h>
	#include <avr/interrupt.h>
	#include <avr/sleep.h>
	#include <util/delay.h>

	#define BAUD 115200 // serial port baud rate
	#define BAUD_TOL 3 // increase the baud rate tolerance to 3%
	#include <util/setbaud.h> // compute USE_2X and UBRR_VALUE

	#define PROLOGUE "== STARTING ==\r\n"

	// ADC interrupt service routine.
	ISR(ADC_vect)
	{
	// Output the 8-bit ADC reading through the serial port.
	UDR0 = ADCH;

	// Switch between ADC channels 0 and 1.
	ADMUX ^= _BV(MUX0);
	}

	int main(void)
	{
	// Configure the serial port.
	UCSR0A = USE_2X << U2X0; // double speed if needed
	UCSR0B = _BV(TXEN0); // enable only the transmitter
	UCSR0C = _BV(UCSZ00) // character size = 8 bits
	\| _BV(UCSZ01); // ...ditto
	UBRR0 = UBRR_VALUE; // set baud rate

	// Send the prologue.
	for (const char p = PROLOGUE; p; p++) {
	UDR0 = *p; // output
	loop_until_bit_is_set(UCSR0A, UDRE0); // flush
	}

	// Configure the ADC in "free running mode".
	DIDR0 = _BV(ADC0D) // disable the digital inputs ADC0...
	\| _BV(ADC1D); // ...and ADC1
	ADMUX = _BV(REFS0) // voltage reference = AVCC
	\| _BV(ADLAR) // left adjust result
	\| 0; // initial input channel = ADC0
	ADCSRB = 0; // auto trigger source = self
	ADCSRA = _BV(ADEN) // enable ADC
	\| _BV(ADSC) // start first conversion
	\| _BV(ADATE) // enable auto trigger
	\| _BV(ADIF) // clear interrupt flag
	\| _BV(ADIE) // enable interrupt
	\| 7; // prescaler = 128
	_delay_us(9); // let the conversion start
	ADMUX \|= _BV(MUX0); // first channel switch

	// Sleep while waiting for interrupts.
	sei();
	sleep_enable();
	for (;;)
	sleep_cpu();
	}