98 lines
3.3 KiB
C
98 lines
3.3 KiB
C
/* ----------------------------------------------------------------------------
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* Copyright (c) 2012, 2013 Ben Blazak <benblazak.dev@gmail.com>
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* Released under The MIT License (see "doc/licenses/MIT.md")
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* Project located at <https://github.com/benblazak/ergodox-firmware>
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* ------------------------------------------------------------------------- */
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/** description
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* Very simple implementation for the Teensy 2.0 (ATmega32U4)
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*
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* - This is mostly straight from the datasheet, section 20.6.6, figure 20-11
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* (the code example in C), and section 20.8.1, figure 20-12
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* - Also see the documentation for `<util/twi.h>` at
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* <http://www.nongnu.org/avr-libc/user-manual/group__util__twi.html#ga8d3aca0acc182f459a51797321728168>
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*
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* Some other (more complete) TWI libraries for the Teensy 2.0 (and other Atmel
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* processors):
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* - [i2cmaster] (http://homepage.hispeed.ch/peterfleury/i2cmaster.zip)
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* - written by [peter-fleury] (http://homepage.hispeed.ch/peterfleury/)
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* - [the arduino twi library]
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* (https://github.com/arduino/Arduino/tree/master/libraries/Wire/utility)
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* - look for an older version if you need one that doesn't depend on all
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* the other Arduino stuff
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*/
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#include <util/twi.h>
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#include "../twi.h"
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// ----------------------------------------------------------------------------
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/** macros/OPT__TWI__FREQUENCY/description
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* Implementation notes:
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* - The max speed for the ATmega32U4 is 400kHz (datasheet sec. 20.1)
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* - The max speed for the MCP23017 is 1.7MHz (datasheet pg. 1)
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* - The max speed for the MCP23018 is 3.4MHz (datasheet pg. 1)
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*/
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#if OPT__TWI__FREQUENCY > 400000
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#error "OPT__TWI__FREQUENCY must be <= 400000"
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#endif
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// ----------------------------------------------------------------------------
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void twi__init(void) {
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// set the prescaler value to 0
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TWSR &= ~( (1<<TWPS1)|(1<<TWPS0) );
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// set the bit rate
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// - TWBR should be 10 or higher (datasheet section 20.5.2)
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TWBR = ((F_CPU / OPT__TWI__FREQUENCY) - 16) / 2;
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}
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uint8_t twi__start(void) {
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// send start
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TWCR = (1<<TWINT)|(1<<TWEN)|(1<<TWSTA);
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// wait for transmission to complete
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while (!(TWCR & (1<<TWINT)));
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// if it didn't work, return the status code (else return 0)
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if ( (TW_STATUS != TW_START) &&
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(TW_STATUS != TW_REP_START) )
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return TW_STATUS; // error
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return 0; // success
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}
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void twi__stop(void) {
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// send stop
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TWCR = (1<<TWINT)|(1<<TWEN)|(1<<TWSTO);
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// wait for transmission to complete
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while (TWCR & (1<<TWSTO));
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}
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uint8_t twi__send(uint8_t data) {
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// load data into the data register
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TWDR = data;
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// send data
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TWCR = (1<<TWINT)|(1<<TWEN);
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// wait for transmission to complete
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while (!(TWCR & (1<<TWINT)));
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// if it didn't work, return the status code (else return 0)
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if ( (TW_STATUS != TW_MT_SLA_ACK) &&
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(TW_STATUS != TW_MT_DATA_ACK) &&
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(TW_STATUS != TW_MR_SLA_ACK) )
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return TW_STATUS; // error
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return 0; // success
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}
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uint8_t twi__read(uint8_t * data) {
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// read 1 byte to TWDR, send ACK
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TWCR = (1<<TWINT)|(1<<TWEN)|(1<<TWEA);
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// wait for transmission to complete
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while (!(TWCR & (1<<TWINT)));
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// set data variable
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*data = TWDR;
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// if it didn't work, return the status code (else return 0)
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if (TW_STATUS != TW_MR_DATA_ACK)
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return TW_STATUS; // error
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return 0; // success
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}
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