4 Channel Audio Switcher Update

Update

I've been trying to move away from using the arduino environment and work at the bare metal level for avr mcus. As an experiment I decided to rewrite the code for the audio switcher I wrote about here:
 https://inverseaudio.blogspot.com/2020/01/4-channel-audio-switcher.html.

Its only a small amount of code so I didn't really expect much difference in terms of code, but it seemed like a good starting exercise. The code compiled within the arduino environment used 1014 bytes (49%) of the program memory, and 15 bytes (11%) of the dynamic memory.

I was incredibly surprised to find that the version written in pure c, compiled with atmel studio used only 220 btyes (2.7%) of the program memory, and 2 bytes (0.4%) of the dynamic memory.

The only major changes made to the code were the omission of the enum classes, the gpio pin setup, and the setting of the multiplexer pins. In such a small project the space savings weren't entirely necessary. However, I think that the changes arguably made the code more clean and readable if you're familiar with port manipulation and bit shifting. 

Code

	/*
	* Attiny85_audio_switcher.c
	*
	* Version not using any arduino elements
	*
	* Created: 15-Jan-20 11:31:53 AM
	* Author : Zac
	*/
	/* Cpu speed for delay */
	#define F_CPU 1000000
	#include <avr/io.h>
	#include <stdint.h>
	#include <util/delay.h>
	#define NUM_CHANNELS 4
	/* Function prototypes */
	void gpio_init(void);
	void poll_buttons(void);
	void set_mux(void);
	/* Pin defines*/
	const uint8_t MUX_PIN[2] = {PINB3, PINB4};
	const uint8_t BTN_PIN[2] = {PINB0, PINB2};
	/* State variables */
	uint8_t current_channel = 0x00;
	uint8_t previous_channel = 0x00;
	int main(void)
	{
	gpio_init();
	while (1)
	{
	poll_buttons();
	if(previous_channel != current_channel)
	{
	set_mux();
	}
	}
	}
	void gpio_init(void)
	{
	DDRB |= (1U << MUX_PIN[0]) | (1U << MUX_PIN[1]); /* Set mux pins as output */
	DDRB &= ~(1U << BTN_PIN[0]) | (1U << BTN_PIN[1]); /* Set button pins as input */
	}
	void poll_buttons(void)
	{
	/* Increment channel */
	if(PINB & (1U << BTN_PIN[0]))
	{
	previous_channel = current_channel;
	if(current_channel < (NUM_CHANNELS - 1))
	{
	current_channel++;
	}
	_delay_ms(250); /* debounce */
	}
	/* Decrement channel */
	if(PINB & (1U << BTN_PIN[1]))
	{
	previous_channel = current_channel;
	if(current_channel > 0)
	{
	current_channel--;
	}
	_delay_ms(250); /* debounce */
	}
	}
	/* Set mux pins corresponding to bits of current channel variable */
	void set_mux(void)
	{
	for(uint8_t pin = 0; pin < 2; ++pin)
	{
	if(current_channel & (1U << pin))
	{
	PORTB |= (1U << MUX_PIN[pin]); /* Set pin */
	}
	else
	{
	PORTB &= ~(1U << MUX_PIN[pin]); /* Clear pin*/
	}
	}
	}

view raw switcher_v2.c hosted with ❤ by GitHub