adapter/spi_via_usi_driver.c File Reference

#include <avr/io.h>
#include <avr/interrupt.h>

Data Structures
struct	usidriverStatus_t
	Driver status bit structure. More...
Defines
#define	USI_OUT_REG PORTB
	USI port output register.
#define	USI_IN_REG PINE
	USI port input register.
#define	USI_DIR_REG DDRB
	USI port direction register.
#define	USI_CLOCK_PIN PB2
	USI clock I/O pin.
#define	USI_DATAIN_PIN PB1
	USI data input pin.
#define	USI_DATAOUT_PIN PB0
	USI data output pin.
#define	TC0_PRESCALER_VALUE 256
	Must be 1, 8, 64, 256 or 1024.
#define	TC0_COMPARE_VALUE 1
	Must be 0 to 255. Minimum 31 with prescaler CLK/1.
#define	TC0_PS_SETTING (1<<CS02)
Functions
	ISR (SIG_USI_OVERFLOW)
	Timer/Counter 0 Compare Match Interrupt handler.
void	spiX_initmaster (char spi_mode)
	Initialize USI as SPI master.
void	spiX_initslave (char spi_mode)
	Initialize USI as SPI slave.
char	spiX_put (unsigned char val)
	Put one byte on bus.
unsigned char	spiX_get (void)
	Get one byte from bus.
void	spiX_wait (void)
	Wait for transfer to complete.
Variables
unsigned char	storedUSIDR
	Data input register buffer.
struct usidriverStatus_t	spiX_status
	The driver status bits.

Detailed Description

Atmel Corporation

File: spi_via_usi_driver.c
Compiler: IAR EWAAVR 3.10c
Support mail: avr@atmel.com

Supported devices: All devices with Universal Serial Interface (USI) capabilities can be used. The example is written for ATmega169.

AppNote: AVR319 - Using the USI module for SPI communication.

Description: Example on how to use the USI module for communicating with SPI compatible devices. The functions and variables prefixed 'spiX_' can be renamed to be able to use several spi drivers (using different interfaces) with similar names. Some basic SPI knowledge is assumed.

Revision: 1.4

Date: Monday, September 13, 2004 12:08:54 UTC

Definition in file spi_via_usi_driver.c.

Define Documentation

#define TC0_COMPARE_VALUE 1

Must be 0 to 255. Minimum 31 with prescaler CLK/1.

Definition at line 46 of file spi_via_usi_driver.c.

Referenced by spiX_initmaster().

#define TC0_PRESCALER_VALUE 256

Must be 1, 8, 64, 256 or 1024.

Definition at line 45 of file spi_via_usi_driver.c.

#define TC0_PS_SETTING (1<<CS02)

Definition at line 60 of file spi_via_usi_driver.c.

Referenced by spiX_initmaster().

#define USI_CLOCK_PIN PB2

USI clock I/O pin.

Definition at line 34 of file spi_via_usi_driver.c.

Referenced by spiX_initmaster(), and spiX_initslave().

#define USI_DATAIN_PIN PB1

USI data input pin.

Definition at line 35 of file spi_via_usi_driver.c.

Referenced by spiX_initmaster(), and spiX_initslave().

#define USI_DATAOUT_PIN PB0

USI data output pin.

Definition at line 36 of file spi_via_usi_driver.c.

Referenced by spiX_initmaster(), and spiX_initslave().

#define USI_DIR_REG DDRB

USI port direction register.

Definition at line 33 of file spi_via_usi_driver.c.

Referenced by spiX_initmaster(), and spiX_initslave().

#define USI_IN_REG PINE

USI port input register.

Definition at line 32 of file spi_via_usi_driver.c.

#define USI_OUT_REG PORTB

USI port output register.

Definition at line 31 of file spi_via_usi_driver.c.

Referenced by spiX_initmaster(), and spiX_initslave().

Function Documentation

ISR ( SIG_USI_OVERFLOW )

Timer/Counter 0 Compare Match Interrupt handler.

This interrupt handler is only enabled when transferring data in master mode. It toggles the USI clock pin, i.e. two interrupts results in one clock period on the clock pin and for the USI counter.

USI Timer Overflow Interrupt handler. This handler disables the compare match interrupt if in master mode. When the USI counter overflows, a byte has been transferred, and we have to stop the timer tick. For all modes the USIDR contents are stored and flags are updated.

Definition at line 118 of file spi_via_usi_driver.c.

00119 {
00120   // Master must now disable the compare match interrupt
00121   // to prevent more USI counter clocks.
00122   if( spiX_status.masterMode == 1 ) {
00123     TIMSK &= ~(1<<OCIE0A);
00124   }
00125 
00126   // Update flags and clear USI counter
00127   USISR = (1<<USIOIF);
00128   spiX_status.transferComplete = 1;
00129 
00130   // Copy USIDR to buffer to prevent overwrite on next transfer.
00131   storedUSIDR = USIDR;
00132 }

unsigned char spiX_get ( void )

Get one byte from bus.

This function only returns the previous stored USIDR value. The transfer complete flag is not checked. Use this function like you would read from the SPDR register in the native SPI module.

Definition at line 248 of file spi_via_usi_driver.c.

00249 {
00250   return storedUSIDR;
00251 }

void spiX_initmaster ( char spi_mode )

Initialize USI as SPI master.

This function sets up all pin directions and module configurations. Use this function initially or when changing from slave to master mode. Note that the stored USIDR value is cleared.

Parameters:

spi_mode

Required SPI mode, must be 0 or 1.

Definition at line 144 of file spi_via_usi_driver.c.

00145 {
00146   // Configure port directions.
00147   USI_DIR_REG |= (1<<USI_DATAOUT_PIN) | (1<<USI_CLOCK_PIN); // Outputs.
00148   USI_DIR_REG &= ~(1<<USI_DATAIN_PIN);                      // Inputs.
00149   USI_OUT_REG |= (1<<USI_DATAIN_PIN);                       // Pull-ups.
00150 
00151   // Configure USI to 3-wire master mode with overflow interrupt.
00152   USICR = (1<<USIOIE) | (1<<USIWM0) |
00153           (1<<USICS1) | (spi_mode<<USICS0) |
00154           (1<<USICLK);
00155 
00156   // Enable 'Clear Timer on Compare match' and init prescaler.
00157   TCCR0A = TC0_PS_SETTING;
00158 
00159   //TCCR0A = (1<<WGM01);
00160 
00161   // Init Output Compare Register.
00162   OCR0A = TC0_COMPARE_VALUE;
00163 
00164   // Init driver status register.
00165   spiX_status.masterMode       = 1;
00166   spiX_status.transferComplete = 0;
00167   spiX_status.writeCollision   = 0;
00168 
00169   storedUSIDR = 0;
00170 }

void spiX_initslave ( char spi_mode )

Initialize USI as SPI slave.

This function sets up all pin directions and module configurations. Use this function initially or when changing from master to slave mode. Note that the stored USIDR value is cleared.

Parameters:

spi_mode

Required SPI mode, must be 0 or 1.

Definition at line 182 of file spi_via_usi_driver.c.

00183 {
00184   // Configure port directions.
00185   USI_DIR_REG |= (1<<USI_DATAOUT_PIN);                      // Outputs.
00186   USI_DIR_REG &= ~(1<<USI_DATAIN_PIN) | (1<<USI_CLOCK_PIN); // Inputs.
00187   USI_OUT_REG |= (1<<USI_DATAIN_PIN) | (1<<USI_CLOCK_PIN);  // Pull-ups.
00188 
00189   // Configure USI to 3-wire slave mode with overflow interrupt.
00190   USICR = (1<<USIOIE) | (1<<USIWM0) |
00191           (1<<USICS1) | (spi_mode<<USICS0);
00192 
00193   // Init driver status register.
00194   spiX_status.masterMode       = 0;
00195   spiX_status.transferComplete = 0;
00196   spiX_status.writeCollision   = 0;
00197 
00198   storedUSIDR = 0;
00199 }

char spiX_put ( unsigned char val )

Put one byte on bus.

Use this function like you would write to the SPDR register in the native SPI module. Calling this function in master mode starts a transfer, while in slave mode, a byte will be prepared for the next transfer initiated by the master device. If a transfer is in progress, this function will set the write collision flag and return without altering the data registers.

Returns:: 0 if a write collision occurred, 1 otherwise.

Definition at line 213 of file spi_via_usi_driver.c.

00214 {
00215   // Check if transmission in progress,
00216   // i.e. USI counter unequal to zero.
00217   if( (USISR & 0x0F) != 0 ) {
00218     // Indicate write collision and return.
00219     spiX_status.writeCollision = 1;
00220     return 1;
00221   }
00222 
00223   // Reinit flags.
00224   spiX_status.transferComplete = 0;
00225   spiX_status.writeCollision = 0;
00226 
00227   // Put data in USI data register.
00228   USIDR = val;
00229 
00230   // Master should now enable compare match interrupts.
00231   if( spiX_status.masterMode == 1 ) {
00232     TIFR |= (1<<OCF0A);   // Clear compare match flag.
00233     TIMSK |= (1<<OCIE0A); // Enable compare match interrupt.
00234   }
00235 
00236   if( spiX_status.writeCollision == 0 ) return 1;
00237   return 0;
00238 }

void spiX_wait ( void )

Wait for transfer to complete.

This function waits until the transfer complete flag is set. Use this function like you would wait for the native SPI interrupt flag.

Definition at line 260 of file spi_via_usi_driver.c.

00261 {
00262   do {} while( spiX_status.transferComplete == 0 );
00263 }

Variable Documentation

struct usidriverStatus_t spiX_status

The driver status bits.

Definition at line 93 of file spi_via_usi_driver.c.

Referenced by ISR(), spiX_initmaster(), spiX_initslave(), spiX_put(), and spiX_wait().

unsigned char storedUSIDR

Data input register buffer.

Incoming bytes are stored in this byte until the next transfer is complete. This byte can be used the same way as the SPI data register in the native SPI module, which means that the byte must be read before the next transfer completes and overwrites the current value.

Definition at line 76 of file spi_via_usi_driver.c.

Referenced by ISR(), spiX_get(), spiX_initmaster(), and spiX_initslave().

adapter/spi_via_usi_driver.c File Reference

Data Structures

Defines

Functions

Variables

Detailed Description

Define Documentation

Function Documentation

Variable Documentation