Basic boilerplate for programming AVR (arduino) in C.
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#include <avr/io.h>
#include <stdint.h>
#include <stdbool.h>
#include "iopins.h"
#include "spi.h"
/** Init SPI (for SD card communication) */
void spi_init_master(enum SPI_order order, enum SPI_cpol cpol, enum SPI_cpha cpha, enum SPI_clk_div clkdiv)
{
as_output(PIN_SS); // SS output - we control slave
as_output(PIN_MOSI); // MOSI output - we talk to slave
as_output(PIN_SCK); // SCK output - we're generating clock
// MISO is configured automatically as input
SPCR = 0;
SPCR |= (1 << MSTR);
SPCR |= (order << DORD);
SPCR |= (cpol << CPOL);
SPCR |= (cpha << CPHA);
// speed
SPCR |= (clkdiv & 0b11);
SPSR = (bool)(clkdiv & 0b100); // write SPI2X flag
// enable SPI
SPCR |= (1 << SPE);
}
/** Init SPI (for SD card communication) */
void spi_init_slave(enum SPI_order order, enum SPI_cpol cpol, enum SPI_cpha cpha)
{
as_output(PIN_MISO); // we're listening to master
// MOSI, SS, SCK are configured automatically
SPCR = 0;
SPCR |= (order << DORD);
SPCR |= (cpol << CPOL);
SPCR |= (cpha << CPHA);
// enable SPI
SPCR |= (1 << SPE);
}
/** Write a byte to SPI. Returns received byte. */
uint8_t spi_send(uint8_t byte)
{
SPDR = byte;
while (bit_is_low(SPSR, SPIF));
return SPDR;
}
/** Receive (as slave). Blocking. */
uint8_t spi_receive(uint8_t reply)
{
SPDR = reply;
while (bit_is_low(SPSR, SPIF));
return SPDR;
}