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i2c.c: review error handling yet again. 

- Flag I2C_MODE_FREE was misleading, because one couldn't test
   for it the same way as for I2C_MODE_BUSY. At an error
   condition, 'i2c_mode & I2C_MODE_FREE' would still evaluate
   to true.

 - On error, drop not only the buffer, but the entire
   transmission.

All of a sudden, the display works reliably, even at the
previously shaky speed of 100'000 bits/s!

TBH, probably I didn't understand some parts of Ruslan's code
earlier but tweaked it anyways. Shame on me!
This commit is contained in:
Markus Hitter 2016-04-26 23:21:35 +02:00
parent 6e8067208e
commit d803883cdb
1 changed files with 18 additions and 17 deletions
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35
i2c.c
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@ -57,13 +57,9 @@
#define I2C_MODE_ENHA 0b00001000
// Transponder is busy.
#define I2C_MODE_BUSY 0b01000000
// Transponder is free.
#define I2C_MODE_FREE 0b10111111
// Transmission interrupted.
#define I2C_INTERRUPTED 0b10000000
// Transmission not interrupted.
#define I2C_NOINTERRUPTED 0b01111111
#define I2C_ERROR 0b00000001
#define I2C_ERROR_LOW_PRIO 0b00100000
@ -73,7 +69,7 @@
uint8_t i2c_address;
// State of TWI component of MCU.
volatile uint8_t i2c_state = I2C_MODE_FREE;
volatile uint8_t i2c_state = 0;
/**
Wether transmission should be terminated on buffer drain. This also means
@ -207,19 +203,20 @@ uint8_t i2c_busy(void) {
*/
void i2c_write(uint8_t data, uint8_t last_byte) {
// Drop characters until transmission end. Transmissions to the display
// start with a command byte, so sending truncated transmissions is harmful.
if (i2c_state & I2C_ERROR) {
if (last_byte) {
i2c_state &= ~I2C_ERROR;
}
return;
}
while (i2c_should_end || ! buf_canwrite(send)) {
delay_us(10);
}
// Recover from error conditions by draining the buffer.
if (i2c_state & I2C_ERROR) {
while (buf_canread(send)) {
buf_pop(send, TWDR);
}
i2c_state = I2C_MODE_FREE;
}
if (i2c_state & I2C_MODE_FREE) {
if ( ! (i2c_state & I2C_MODE_BUSY)) {
// No transmission ongoing, start one.
i2c_state = I2C_MODE_SAWP;
TWCR = (1<<TWINT)|(0<<TWEA)|(1<<TWSTA)|(0<<TWSTO)|(1<<TWEN)|(1<<TWIE);
@ -328,7 +325,7 @@ ISR(TWI_vect) {
TWCR = (1<<TWINT)|(I2C_MODE<<TWEA)|(0<<TWSTA)|(0<<TWSTO)|(1<<TWEN)|(1<<TWIE);
} else {
// Buffer drained because transmission is completed.
i2c_state = I2C_MODE_FREE;
i2c_state = 0;
i2c_should_end = 0;
// Send stop condition.
TWCR = (1<<TWINT)|(I2C_MODE<<TWEA)|(0<<TWSTA)|(1<<TWSTO)|(1<<TWEN)|(0<<TWIE);
@ -470,7 +467,7 @@ ISR(TWI_vect) {
// We sent the last byte and received NACK or ACK (doesn't matter here).
if (i2c_state & I2C_INTERRUPTED) {
// There was interrupted master transfer.
i2c_state &= I2C_NOINTERRUPTED;
i2c_state &= ~I2C_INTERRUPTED;
// Generate start as the bus became free.
TWCR = (1<<TWINT)|(1<TWEA)|(1<<TWSTA)|(0<<TWSTO)|(1<<TWEN)|(1<<TWIE);
} else {
@ -507,9 +504,13 @@ ISR(TWI_vect) {
serial_writechar('8');
#endif
i2c_state |= I2C_ERROR;
i2c_state |= I2C_ERROR | I2C_INTERRUPTED;
// Let i2c_write() continue.
i2c_should_end = 0;
// Drain the buffer.
while (buf_canread(send)) {
buf_pop(send, TWDR);
}
// Send stop condition.
TWCR = (1<<TWINT)|(I2C_MODE<<TWEA)|(0<<TWSTA)|(1<<TWSTO)|(1<<TWEN)|(0<<TWIE);
break;