atmega_spi.c File Reference

Driver for SPI communication between the ATmega328P and other SPI compatible devices. More...

#include <avr/io.h>
#include <avr/interrupt.h>
#include "atmega_spi.h"
#include "pin_defines.h"

Go to the source code of this file.

Functions
void	init_spi (spi_transfer_mode_t transfer_mode, spi_control_mode_t control_mode, spi_polarity_mode_t polarity_mode, spi_phase_mode_t phase_mode, spi_clk_rate_t clk_rate, spi_dbl_clk_mode_t dbl_clock)
	Initialisation routine to set up SPI comms. More...
uint8_t	spi_trade_byte (uint8_t data)
	Sends out a byte of data over SPI and returns the byte it receives. More...
uint16_t	spi_trade_word (uint16_t data)
	Sends out a 16bit word of data over spi (in two bytes) and returns the byte it receives. More...

Detailed Description

Driver for SPI communication between the ATmega328P and other SPI compatible devices.

Copyright

Copyright © 2022 by Jason Duffy.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Author

Jason Duffy

Date

9th April 2022

This file provides the basic SPI comms setup and initialisation instructions. The following ports/pins must be defined in pin_defines.h: SPI_DDR, SPI_PORT, SPI_MOSI SPI_MISO, SPI_SCK, SPI_SS.

Definition in file atmega_spi.c.

Function Documentation

init_spi()

void init_spi	(	spi_transfer_mode_t	transfer_mode,
		spi_control_mode_t	control_mode,
		spi_polarity_mode_t	polarity_mode,
		spi_phase_mode_t	phase_mode,
		spi_clk_rate_t	clk_rate,
		spi_dbl_clk_mode_t	dbl_clock
	)

Initialisation routine to set up SPI comms.

Must be called before any other functions in this file can be used.

Parameters

transfer_mode	lsb_first or msb_first.
control_mode	controller or peripheral.
polarity_mode	rising_edge or falling_edge.
phase_mode	lead_sample_rising_edge or lead_setup_rising_edge.
clk_rate	Sets the speed of the SPI clock - divided down from F_CPU speed.
dbl_clock	single_speed or double_speed.

Definition at line 53 of file atmega_spi.c.

{
    SPI_DDR |= (1 << SPI_MOSI); // Set MOSI as output.
    SPI_DDR |= (1 << SPI_SCK); // Set SCK as output.
    SPI_DDR &= ~(1 << SPI_MISO); // Set MISO as input. 
    SPI_DDR &= ~(1 << SPI_SS); // Set SS as input.
    SPI_PORT |= (1 << SPI_MISO); // Set pullup on MISO.
    SPI_PORT |= (1 << SPI_SS); // Set pullup on SS.
 
    cli(); // Clear interrupt enable flag.
    SPCR |= (transfer_mode << DORD); // Set data order.
    SPCR |= (control_mode << MSTR); // Controller/peripheral mode select.
    SPCR |= (polarity_mode << CPOL); // Set polarity of SPI data. 
    SPCR |= (phase_mode << CPHA); // Set phase of SPI data.
    SPCR |= (clk_rate); // Set speed
 
    SPSR |= (dbl_clock << SPI2X); // Set double speed bit. 
 
    SPCR |= (1 << SPE); // Enable SPI. 
 
    sei(); // Set interrupt enable flag.
}

spi_trade_byte()

uint8_t spi_trade_byte

(

uint8_t

data

)

Sends out a byte of data over SPI and returns the byte it receives.

Parameters

uint8_t

data: The byte of data to be sent from the host MCU to the peripheral device.

Returns

The data received from the peripheral device is returned.

Definition at line 85 of file atmega_spi.c.

{
    SPDR = data; // Send out byte of data. 
    loop_until_bit_is_set(SPSR, SPIF); // Wait for flag to be set. 
    data = SPDR; // Store the data received. 
    return data;
}

spi_trade_word()

uint16_t spi_trade_word

(

uint16_t

data

)

Sends out a 16bit word of data over spi (in two bytes) and returns the byte it receives.

Parameters

uint16_t

data: The byte of data to be sent from the host MCU to the peripheral device.

Returns

The data received from the peripheral device is returned.

Definition at line 98 of file atmega_spi.c.

{
    uint8_t msb = 0;
    uint8_t lsb = 0;
 
    // Split word to send into 2 bytes and send the first one out. 
    msb |= (data >> 8U);
    lsb |= (data);
    SPDR = msb; 
    loop_until_bit_is_set(SPSR, SPIF);
    msb = SPDR; // Store the byte received. 
 
    // Send the second byte out. 
    SPDR = lsb;
    loop_until_bit_is_set(SPSR, SPIF);
    lsb = SPDR; // Store the second byte received. 
 
    // Combine the bytes received into 1 word. 
    uint16_t received_data = 0;
    received_data = (msb << 8U);
    received_data |= (lsb);
 
    return received_data;
}