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Diffstat (limited to 'keyboards/lets_split/i2c.c')
| -rw-r--r-- | keyboards/lets_split/i2c.c | 162 |
1 files changed, 162 insertions, 0 deletions
diff --git a/keyboards/lets_split/i2c.c b/keyboards/lets_split/i2c.c new file mode 100644 index 0000000000..084c890c40 --- /dev/null +++ b/keyboards/lets_split/i2c.c @@ -0,0 +1,162 @@ +#include <util/twi.h> +#include <avr/io.h> +#include <stdlib.h> +#include <avr/interrupt.h> +#include <util/twi.h> +#include <stdbool.h> +#include "i2c.h" + +#ifdef USE_I2C + +// Limits the amount of we wait for any one i2c transaction. +// Since were running SCL line 100kHz (=> 10μs/bit), and each transactions is +// 9 bits, a single transaction will take around 90μs to complete. +// +// (F_CPU/SCL_CLOCK) => # of μC cycles to transfer a bit +// poll loop takes at least 8 clock cycles to execute +#define I2C_LOOP_TIMEOUT (9+1)*(F_CPU/SCL_CLOCK)/8 + +#define BUFFER_POS_INC() (slave_buffer_pos = (slave_buffer_pos+1)%SLAVE_BUFFER_SIZE) + +volatile uint8_t i2c_slave_buffer[SLAVE_BUFFER_SIZE]; + +static volatile uint8_t slave_buffer_pos; +static volatile bool slave_has_register_set = false; + +// Wait for an i2c operation to finish +inline static +void i2c_delay(void) { + uint16_t lim = 0; + while(!(TWCR & (1<<TWINT)) && lim < I2C_LOOP_TIMEOUT) + lim++; + + // easier way, but will wait slightly longer + // _delay_us(100); +} + +// Setup twi to run at 100kHz +void i2c_master_init(void) { + // no prescaler + TWSR = 0; + // Set TWI clock frequency to SCL_CLOCK. Need TWBR>10. + // Check datasheets for more info. + TWBR = ((F_CPU/SCL_CLOCK)-16)/2; +} + +// Start a transaction with the given i2c slave address. The direction of the +// transfer is set with I2C_READ and I2C_WRITE. +// returns: 0 => success +// 1 => error +uint8_t i2c_master_start(uint8_t address) { + TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTA); + + i2c_delay(); + + // check that we started successfully + if ( (TW_STATUS != TW_START) && (TW_STATUS != TW_REP_START)) + return 1; + + TWDR = address; + TWCR = (1<<TWINT) | (1<<TWEN); + + i2c_delay(); + + if ( (TW_STATUS != TW_MT_SLA_ACK) && (TW_STATUS != TW_MR_SLA_ACK) ) + return 1; // slave did not acknowledge + else + return 0; // success +} + + +// Finish the i2c transaction. +void i2c_master_stop(void) { + TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO); + + uint16_t lim = 0; + while(!(TWCR & (1<<TWSTO)) && lim < I2C_LOOP_TIMEOUT) + lim++; +} + +// Write one byte to the i2c slave. +// returns 0 => slave ACK +// 1 => slave NACK +uint8_t i2c_master_write(uint8_t data) { + TWDR = data; + TWCR = (1<<TWINT) | (1<<TWEN); + + i2c_delay(); + + // check if the slave acknowledged us + return (TW_STATUS == TW_MT_DATA_ACK) ? 0 : 1; +} + +// Read one byte from the i2c slave. If ack=1 the slave is acknowledged, +// if ack=0 the acknowledge bit is not set. +// returns: byte read from i2c device +uint8_t i2c_master_read(int ack) { + TWCR = (1<<TWINT) | (1<<TWEN) | (ack<<TWEA); + + i2c_delay(); + return TWDR; +} + +void i2c_reset_state(void) { + TWCR = 0; +} + +void i2c_slave_init(uint8_t address) { + TWAR = address << 0; // slave i2c address + // TWEN - twi enable + // TWEA - enable address acknowledgement + // TWINT - twi interrupt flag + // TWIE - enable the twi interrupt + TWCR = (1<<TWIE) | (1<<TWEA) | (1<<TWINT) | (1<<TWEN); +} + +ISR(TWI_vect); + +ISR(TWI_vect) { + uint8_t ack = 1; + switch(TW_STATUS) { + case TW_SR_SLA_ACK: + // this device has been addressed as a slave receiver + slave_has_register_set = false; + break; + + case TW_SR_DATA_ACK: + // this device has received data as a slave receiver + // The first byte that we receive in this transaction sets the location + // of the read/write location of the slaves memory that it exposes over + // i2c. After that, bytes will be written at slave_buffer_pos, incrementing + // slave_buffer_pos after each write. + if(!slave_has_register_set) { + slave_buffer_pos = TWDR; + // don't acknowledge the master if this memory loctaion is out of bounds + if ( slave_buffer_pos >= SLAVE_BUFFER_SIZE ) { + ack = 0; + slave_buffer_pos = 0; + } + slave_has_register_set = true; + } else { + i2c_slave_buffer[slave_buffer_pos] = TWDR; + BUFFER_POS_INC(); + } + break; + + case TW_ST_SLA_ACK: + case TW_ST_DATA_ACK: + // master has addressed this device as a slave transmitter and is + // requesting data. + TWDR = i2c_slave_buffer[slave_buffer_pos]; + BUFFER_POS_INC(); + break; + + case TW_BUS_ERROR: // something went wrong, reset twi state + TWCR = 0; + default: + break; + } + // Reset everything, so we are ready for the next TWI interrupt + TWCR |= (1<<TWIE) | (1<<TWINT) | (ack<<TWEA) | (1<<TWEN); +} +#endif |