Add I2C slave library

- Add I2C slave library for general use.

2 files changed, 119 insertions, 0 deletions

diff --git a/drivers/avr/i2c_slave.c b/drivers/avr/i2c_slave.c
new file mode 100755
index 000000000..3edf85b12
--- /dev/null
+++ b/drivers/avr/i2c_slave.c
@@ -0,0 +1,100 @@
+/* Library made by: g4lvanix
+ * Github repository: https://github.com/g4lvanix/I2C-slave-lib
+ */
+
+#include <avr/io.h>
+#include <util/twi.h>
+#include <avr/interrupt.h>
+
+#include "i2c_slave.h"
+
+void i2c_init(uint8_t address){
+        // load address into TWI address register
+        TWAR = (address << 1);
+        // set the TWCR to enable address matching and enable TWI, clear TWINT, enable TWI interrupt
+        TWCR = (1<<TWIE) | (1<<TWEA) | (1<<TWINT) | (1<<TWEN);
+}
+
+void i2c_stop(void){
+        // clear acknowledge and enable bits
+        TWCR &= ~( (1<<TWEA) | (1<<TWEN) );
+}
+
+ISR(TWI_vect){
+        
+        // temporary stores the received data
+        uint8_t data;
+        
+        // own address has been acknowledged
+        if( (TWSR & 0xF8) == TW_SR_SLA_ACK ){  
+                buffer_address = 0xFF;
+                // clear TWI interrupt flag, prepare to receive next byte and acknowledge
+                TWCR |= (1<<TWIE) | (1<<TWINT) | (1<<TWEA) | (1<<TWEN); 
+        }
+        else if( (TWSR & 0xF8) == TW_SR_DATA_ACK ){ // data has been received in slave receiver mode
+                
+                // save the received byte inside data 
+                data = TWDR;
+                
+                // check wether an address has already been transmitted or not
+                if(buffer_address == 0xFF){
+                        
+                        buffer_address = data; 
+                        
+                        // clear TWI interrupt flag, prepare to receive next byte and acknowledge
+                        TWCR |= (1<<TWIE) | (1<<TWINT) | (1<<TWEA) | (1<<TWEN); 
+                }
+                else{ // if a databyte has already been received
+                        
+                        // store the data at the current address
+                        rxbuffer[buffer_address] = data;
+                        
+                        // increment the buffer address
+                        buffer_address++;
+                        
+                        // if there is still enough space inside the buffer
+                        if(buffer_address < 0xFF){
+                                // clear TWI interrupt flag, prepare to receive next byte and acknowledge
+                                TWCR |= (1<<TWIE) | (1<<TWINT) | (1<<TWEA) | (1<<TWEN); 
+                        }
+                        else{
+                                // Don't acknowledge
+                                TWCR &= ~(1<<TWEA); 
+                                // clear TWI interrupt flag, prepare to receive last byte.
+                                TWCR |= (1<<TWIE) | (1<<TWINT) | (1<<TWEN); 
+                        }
+                }
+        }
+        else if( (TWSR & 0xF8) == TW_ST_DATA_ACK ){ // device has been addressed to be a transmitter
+                
+                // copy data from TWDR to the temporary memory
+                data = TWDR;
+                
+                // if no buffer read address has been sent yet
+                if( buffer_address == 0xFF ){
+                        buffer_address = data;
+                }
+                
+                // copy the specified buffer address into the TWDR register for transmission
+                TWDR = txbuffer[buffer_address];
+                // increment buffer read address
+                buffer_address++;
+                
+                // if there is another buffer address that can be sent
+                if(buffer_address < 0xFF){
+                        // clear TWI interrupt flag, prepare to send next byte and receive acknowledge
+                        TWCR |= (1<<TWIE) | (1<<TWINT) | (1<<TWEA) | (1<<TWEN); 
+                }
+                else{
+                        // Don't acknowledge
+                        TWCR &= ~(1<<TWEA); 
+                        // clear TWI interrupt flag, prepare to receive last byte.
+                        TWCR |= (1<<TWIE) | (1<<TWINT) | (1<<TWEN); 
+                }
+                
+        }
+        else{
+                // if none of the above apply prepare TWI to be addressed again
+                TWCR |= (1<<TWIE) | (1<<TWEA) | (1<<TWEN);
+        } 
+}
diff --git a/drivers/avr/i2c_slave.h b/drivers/avr/i2c_slave.h
new file mode 100755
index 000000000..3fda7f8c0
--- /dev/null
+++ b/drivers/avr/i2c_slave.h
@@ -0,0 +1,19 @@
+/* Library made by: g4lvanix
+ * Github repository: https://github.com/g4lvanix/I2C-slave-lib
+
+ Info: Inititate the library by giving the required address.
+       Read or write to the necessary buffer according to the opperation.
+ */
+
+#ifndef I2C_SLAVE_H
+#define I2C_SLAVE_H
+
+volatile uint8_t buffer_address;
+volatile uint8_t txbuffer[0xFF];
+volatile uint8_t rxbuffer[0xFF];
+
+void i2c_init(uint8_t address);
+void i2c_stop(void);
+ISR(TWI_vect);
+
+#endif // I2C_SLAVE_H