From 061225f72d8dcb545cf12938f6280dad633a654b Mon Sep 17 00:00:00 2001
From: Markus Hitter <mah@jump-ing.de>
Date: Sun, 3 Apr 2016 21:08:18 +0200
Subject: [PATCH] I2C: get rid of these unimplemented error handlers.

Naively restarting I2C immediately is certainly not the solution
and just leads to an interrupt flood. As I2C is currently meant
to drive displays, where successful data transmission isn't
crucial, we now simply stop transmission on errors.

This saves another 80 bytes binary size:

    FLASH  : 23094 bytes
    RAM    :  2051 bytes
    EEPROM :    32 bytes
---
 i2c.c    | 53 +++++++++++++++--------------------------------------
 i2c.h    | 19 +------------------
 mendel.c |  2 +-
 3 files changed, 17 insertions(+), 57 deletions(-)

diff --git a/i2c.c b/i2c.c
index 133ff97..ea08c04 100644
--- a/i2c.c
+++ b/i2c.c
@@ -59,12 +59,8 @@ uint8_t i2c_byte_count;
   uint8_t *i2c_buffer;
 #endif /* I2C_SLAVE_MODE */
 
-I2C_HANDLER i2c_master_func = &i2c_do_nothing;
-I2C_HANDLER i2c_slave_func = &i2c_do_nothing;
-I2C_HANDLER i2c_error_func = &i2c_do_nothing;
 
-
-void i2c_init(uint8_t address, I2C_HANDLER func) {
+void i2c_init(uint8_t address) {
 
   i2c_address = address;
 
@@ -74,8 +70,6 @@ void i2c_init(uint8_t address, I2C_HANDLER func) {
       I2C_PORT |= (1 << I2C_SCL_PIN) | (1 << I2C_SDA_PIN);
     #endif /* I2C_ENABLE_PULLUPS */
 
-    i2c_master_func = func;
-
     /**
       TWI Bit Rate register
       SCL_freq = CPU_freq / (16 + 2 * TWBR)
@@ -92,7 +86,6 @@ void i2c_init(uint8_t address, I2C_HANDLER func) {
   #endif /* I2C_MASTER_MODE */
 
   #ifdef I2C_SLAVE_MODE
-    i2c_slave_func = func;
     TWAR = i2c_address; // We listen to broadcasts if lowest bit is set.
     TWCR = (0<<TWINT)|(0<<TWEA)|(0<<TWSTA)|(0<<TWSTO)|(1<<TWEN)|(1<<TWIE);
   #endif
@@ -101,8 +94,6 @@ void i2c_init(uint8_t address, I2C_HANDLER func) {
 static void i2c_send_handler(void) {
 
   i2c_state = I2C_MODE_SAWP; // Just send.
-  i2c_master_func = &i2c_send_handler;
-  i2c_error_func = &i2c_send_handler;
 
   // Start transmission.
   TWCR = (1<<TWINT)|(0<<TWEA)|(1<<TWSTA)|(0<<TWSTO)|(1<<TWEN)|(1<<TWIE);
@@ -122,12 +113,6 @@ void i2c_send(uint8_t address, uint8_t* block, uint8_t tx_len) {
   i2c_send_handler();
 }
 
-/**
-  Empty handler.
-*/
-void i2c_do_nothing(void) {
-}
-
 /**
   This is the interrupt for all the I2C things.
 
@@ -163,8 +148,8 @@ ISR(TWI_vect) {
     case TW_BUS_ERROR:
       // A hardware error was detected.
       i2c_state |= I2C_ERROR_BUS_FAIL;
-      TWCR = (1<<TWINT)|(I2C_MODE<<TWEA)|(0<<TWSTA)|(1<<TWSTO)|(1<<TWEN)|(1<<TWIE);
-      MACRO_I2C_ERROR;
+      // Send stop condition.
+      TWCR = (1<<TWINT)|(I2C_MODE<<TWEA)|(0<<TWSTA)|(1<<TWSTO)|(1<<TWEN)|(0<<TWIE);
       break;
     case TW_START:
       // Start happens, send a target address.
@@ -202,8 +187,8 @@ ISR(TWI_vect) {
     case TW_MT_SLA_NACK:
       // SLA+W was sent, got NACK, so slave is busy or out of bus.
       i2c_state |= I2C_ERROR_NO_ANSWER;
-      TWCR = (1<<TWINT)|(I2C_MODE<<TWEA)|(0<<TWSTA)|(1<<TWSTO)|(1<<TWEN)|(1<<TWIE);
-      MACRO_I2C_ERROR;
+      // Send stop condition.
+      TWCR = (1<<TWINT)|(I2C_MODE<<TWEA)|(0<<TWSTA)|(1<<TWSTO)|(1<<TWEN)|(0<<TWIE);
       break;
     case TW_MT_DATA_ACK:
       // A byte was sent, got ACK.
@@ -236,8 +221,8 @@ ISR(TWI_vect) {
       //  - a slave stops transmission and it is ok, or
       //  - a slave became crazy.
       i2c_state |= I2C_ERROR_NACK;
-      TWCR = (1<<TWINT)|(I2C_MODE<<TWEA)|(0<<TWSTA)|(1<<TWSTO)|(1<<TWEN)|(1<<TWIE);
-      MACRO_I2C_MASTER; // process exit state
+      // Send stop condition.
+      TWCR = (1<<TWINT)|(I2C_MODE<<TWEA)|(0<<TWSTA)|(1<<TWSTO)|(1<<TWEN)|(0<<TWIE);
       break;
     case TW_MT_ARB_LOST:  // Collision, identical to TW_MR_ARB_LOST.
       // It looks like there is another master on the bus.
@@ -264,8 +249,8 @@ ISR(TWI_vect) {
     case TW_MR_SLA_NACK:
       // SLA+R was sent, got NАСК, it seems the slave is busy.
       i2c_state |= I2C_ERROR_NO_ANSWER;
-      TWCR = (1<<TWINT)|(I2C_MODE<<TWEA)|(0<<TWSTA)|(1<<TWSTO)|(1<<TWEN)|(1<<TWIE);
-      MACRO_I2C_ERROR;
+      // Send stop condition.
+      TWCR = (1<<TWINT)|(I2C_MODE<<TWEA)|(0<<TWSTA)|(1<<TWSTO)|(1<<TWEN)|(0<<TWIE);
       break;
     case TW_MR_DATA_ACK:
       i2c_buffer[i2c_index++] = TWDR;
@@ -281,8 +266,8 @@ ISR(TWI_vect) {
     case TW_MR_DATA_NACK:
       // Last byte received, send NACK to make the slave to release the bus.
       i2c_buffer[i2c_index] = TWDR;
-      TWCR = (1<<TWINT)|(I2C_MODE<<TWEA)|(0<<TWSTA)|(1<<TWSTO)|(1<<TWEN)|(1<<TWIE);
-      MACRO_I2C_MASTER;
+      // Send stop condition.
+      TWCR = (1<<TWINT)|(I2C_MODE<<TWEA)|(0<<TWSTA)|(1<<TWSTO)|(1<<TWEN)|(0<<TWIE);
       break;
 
     #ifdef I2C_SLAVE_MODE
@@ -322,15 +307,8 @@ ISR(TWI_vect) {
     case TW_SR_DATA_NACK:
     case TW_SR_GCALL_DATA_NACK:
       i2c_in_buffer[i2c_index] = TWDR;
-      if (i2c_state & I2C_INTERRUPTED) {
-        // Если у нас был прерываный сеанс от имени мастера
-        // Влепим в шину свой Start поскорей и сделаем еще одну попытку
-        TWCR = (1<<TWINT)|(1<TWEA)|(1<<TWSTA)|(0<<TWSTO)|(1<<TWEN)|(1<<TWIE);
-      } else {
-        // Если не было такого факта, то просто отвалимся и будем ждать
-        TWCR = (1<<TWINT)|(1<TWEA)|(0<<TWSTA)|(0<<TWSTO)|(1<<TWEN)|(1<<TWIE);
-      }
-      MACRO_I2C_SLAVE;
+      // Send stop condition.
+      TWCR = (1<<TWINT)|(I2C_MODE<<TWEA)|(0<<TWSTA)|(1<<TWSTO)|(1<<TWEN)|(0<<TWIE);
       break;
     case TW_SR_STOP:
       // We got a Restart. What we will do?
@@ -378,10 +356,9 @@ ISR(TWI_vect) {
         // Generate start as the bus became free.
         TWCR = (1<<TWINT)|(1<TWEA)|(1<<TWSTA)|(0<<TWSTO)|(1<<TWEN)|(1<<TWIE);
       } else {
-        // If we alone then just release the bus.
-        TWCR = (1<<TWINT)|(1<TWEA)|(0<<TWSTA)|(0<<TWSTO)|(1<<TWEN)|(1<<TWIE);
+        // Send stop condition.
+        TWCR = (1<<TWINT)|(I2C_MODE<<TWEA)|(0<<TWSTA)|(1<<TWSTO)|(1<<TWEN)|(0<<TWIE);
       }
-      MACRO_I2C_SLAVE;
       break;
 
     #endif /* I2C_SLAVE_MODE */
diff --git a/i2c.h b/i2c.h
index aa91ff9..051ef92 100644
--- a/i2c.h
+++ b/i2c.h
@@ -54,26 +54,9 @@
 #define I2C_ERROR_NO_ANSWER             0b00010000
 #define I2C_ERROR_LOW_PRIO              0b00100000
 
-#define MACRO_I2C_ERROR         (i2c_error_func)()
-#ifdef I2C_SLAVE_MODE
-  #define MACRO_I2C_SLAVE         (i2c_slave_func)()
-#else
-  #define MACRO_I2C_MASTER        (i2c_master_func)()
-#endif /* I2C_SLAVE_MODE */
 
-
-typedef void (*I2C_HANDLER)(void);
-
-extern I2C_HANDLER i2c_error_func;
-#ifdef I2C_SLAVE_MODE
-  extern I2C_HANDLER i2c_slave_func;
-#else
-  extern I2C_HANDLER i2c_master_func;
-#endif /* I2C_SLAVE_MODE */
-
-void i2c_init(uint8_t address, I2C_HANDLER func);
+void i2c_init(uint8_t address);
 void i2c_send(uint8_t address, uint8_t* block, uint8_t tx_len);
-void i2c_do_nothing(void);
 
 #endif /* I2C */
 
diff --git a/mendel.c b/mendel.c
index 36774bd..a6280f8 100644
--- a/mendel.c
+++ b/mendel.c
@@ -96,7 +96,7 @@ void init(void) {
   #endif
 
   #ifdef I2C
-    i2c_init(DISPLAY_I2C_ADDRESS, i2c_do_nothing);
+    i2c_init(DISPLAY_I2C_ADDRESS);
   #endif
 
 	// set up timers