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/*
* Copyright © 2011 Keith Packard <keithp@keithp.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; version 2 of the License.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
*/
#include <ao.h>
/*
* ATtiny USI as an I2C interface
*/
#define I2C_USICR ((0 << USISIE) | /* No start condition interrupt */ \
(0 << USIOIE) | /* No counter overflow interrupt */ \
(1 << USIWM1) | /* Two-wire mode */ \
(0 << USIWM0) | /* ... */ \
(1 << USICS1) | /* Software clock strobe */ \
(0 << USICS0) | /* ... */ \
(1 << USICLK)) /* ... */ \
#define I2C_USICR_TICK (I2C_USICR | (1 << USITC)) /* Toggle the clock on every write */
#define I2C_USISR_1BIT ((1<<USISIF)| /* Clear start condition flag */ \
(1<<USIOIF)| /* Clear overflow flag */ \
(1<<USIPF)| /* Clear stop condition flag */ \
(1<<USIDC)| /* Clear data collision flag */ \
(0xE<<USICNT0)) /* Set counter value to 0xe */
#define I2C_USISR_8BIT ((1<<USISIF)| /* Clear start condition flag */ \
(1<<USIOIF)| /* Clear overflow flag */ \
(1<<USIPF)| /* Clear stop condition flag */ \
(1<<USIDC)| /* Clear data collision flag */ \
(0x0<<USICNT0)) /* Set counter value to 0 */
#define T2_TWI 5 /* >4.7μs */
#define T4_TWI 4 /* >4.0μs */
static inline void ao_i2c_transfer(uint8_t sr)
{
USISR = sr;
for (;;) {
ao_delay_us(T2_TWI);
/* Clock high */
USICR = I2C_USICR_TICK;
/* Wait for clock high (clock stretching) */
ao_delay_us(T4_TWI);
while(!(I2C_PIN & (1<<I2C_PIN_SCL)))
;
/* Clock low */
USICR = I2C_USICR_TICK;
/* Check for transfer complete */
if (USISR & (1 << USIOIF))
break;
}
ao_delay_us(T2_TWI);
}
static inline uint8_t ao_i2c_get_byte(uint8_t sr)
{
uint8_t ret;
/* Set SDA to input */
I2C_DIR &= ~(1<<I2C_PIN_SDA);
ao_i2c_transfer(sr);
ret = USIDR;
USIDR = 0xff;
/* Set SDA to output */
I2C_DIR |= (1<<I2C_PIN_SDA);
return ret;
}
static uint8_t
ao_i2c_write_byte(uint8_t byte)
{
/* Pull SCL low */
I2C_PORT &= ~(1<<I2C_PIN_SCL);
/* Write the byte */
USIDR = byte;
/* Clock and verify (N)ACK from slave */
ao_i2c_transfer(I2C_USISR_8BIT);
if (ao_i2c_get_byte(I2C_USISR_1BIT) & 0x80)
return 0;
return 1;
}
static uint8_t
ao_i2c_read_byte(uint8_t ack)
{
uint8_t ret;
/* Read the data */
ret = ao_i2c_get_byte(I2C_USISR_8BIT);
/* Ack it */
USIDR = ack;
ao_i2c_transfer(I2C_USISR_8BIT);
return ret;
}
uint8_t
ao_i2c_start_bus(uint8_t address)
{
/* Release SCL to ensure that (repeated) Start can be performed */
I2C_PORT |= (1<<I2C_PIN_SCL);
while( !(I2C_PORT & (1<<I2C_PIN_SCL)) )
;
ao_delay_us(T2_TWI);
/* Generate Start Condition */
/* Pull SDA low */
I2C_PORT &= ~(1<<I2C_PIN_SDA);
ao_delay_us(T4_TWI);
/* Pull SCL low */
I2C_PORT &= ~(1<<I2C_PIN_SCL);
/* Raise SDA */
I2C_PORT |= (1<<I2C_PIN_SDA);
return ao_i2c_write_byte(address);
}
static void
ao_i2c_stop_bus(void)
{
/* Pull SDA low. */
I2C_PORT &= ~(1<<I2C_PIN_SDA);
/* Release SCL. */
I2C_PORT |= (1<<I2C_PIN_SCL);
/* Wait for SCL to go high */
while( !(I2C_PIN & (1<<I2C_PIN_SCL)) );
ao_delay_us(T4_TWI);
/* Raise SDA */
I2C_PORT |= (1<<I2C_PIN_SDA);
ao_delay_us(T2_TWI);
}
/* Send bytes over SPI.
*
* This just polls; the SPI is set to go as fast as possible,
* so using interrupts would take way too long
*/
uint8_t
ao_i2c_send_bus(void __xdata *block, uint16_t len, uint8_t stop)
{
uint8_t *d = block;
while (len--)
if (!ao_i2c_write_byte (*d++))
return 0;
if (stop)
ao_i2c_stop_bus();
return 1;
}
/* Send bytes over SPI.
*
* This just polls; the SPI is set to go as fast as possible,
* so using interrupts would take way too long
*/
uint8_t
ao_i2c_send_fixed_bus(uint8_t d, uint16_t len, uint8_t stop)
{
while (len--)
if (!ao_i2c_write_byte (d))
return 0;
if (stop)
ao_i2c_stop_bus();
return 1;
}
/* Receive bytes over SPI.
*
* Poll, sending zeros and reading data back
*/
uint8_t
ao_i2c_recv_bus(void __xdata *block, uint16_t len, uint8_t stop)
{
uint8_t *d = block;
while (len--)
*d++ = ao_i2c_read_byte (len ? 0x00 : 0xff);
if (stop)
ao_i2c_stop_bus();
return 1;
}
/*
* Initialize USI
*
* Chip select is the responsibility of the caller
*/
void
ao_i2c_init(void)
{
/* Pull-ups on SDA and SCL */
I2C_PORT |= (1<<I2C_PIN_SDA);
I2C_PORT |= (1<<I2C_PIN_SCL);
/* SCL and SDA are outputs */
I2C_DIR |= (1<<I2C_PIN_SCL);
I2C_DIR |= (1<<I2C_PIN_SDA);
USIDR = 0xFF;
USICR = I2C_USICR;
}
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