--- /dev/null
+/*
+ * 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;
+}
projects / fw / altos / blobdiff