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--- robotics:computing:communication_twi_entre_atmega [2013/09/27 15:49]
ldo [Slave]
+++ robotics:computing:communication_twi_entre_atmega [2013/09/27 15:56] (Version actuelle)
ldo [Master]
@@ Ligne 169: / Ligne 169: @@
 Ce code permet d'envoyer une donnée à un esclave.
-Dans un premier temps, on va définir la vitesse de communication en initialisant TWBR et le prescaler dans twiMasterInitialise().
+Dans un premier temps, on va définir la vitesse de communication en initialisant TWBR et le prescaler dans twi_master_setup().
 <code c>
 /*
@@ Ligne 178: / Ligne 178: @@
  */
-/* ATMEGA48 @20MHz
+volatile uint8_t slave_address;
- * pull up resistor 1.5kohm
- * LOW FUSE : F7
- * CKDIV8=1		no divided clock by 8
- * CKOUT=1		no clock output on PORTB
- * SUT1..0=11	slowly rising power
- * CKSEL3..0=0111	full swing crystal oscillator
-	*/
-#include<util/twi.h>
+volatile uint8_t twi_flag_read_complete = 1;
+volatile uint8_t twi_flag_write_complete = 1;
-//sets bitrate and prescaler
+volatile uint8_t *twi_receive_buffer;
-void twiMasterInitialise(unsigned char bitRate, unsigned char prescaler)
+volatile uint8_t *twi_transmit_buffer;
+volatile uint8_t twi_i = 0;
+uint8_t twi_mode;
+uint8_t twi_nb_data_to_transmit, twi_nb_data_to_receive;
+ISR(TWI_vect)
 {
-	PRR = (0 << PRTWI); // the PRTWI bit in PRR must be written to zero to enable the TWI
+  uint8_t status;
-	TWSR = prescaler & 0x03;
-	TWBR = bitRate;
+  status = TWSR & 0xF8;
+  switch (status)
+    {
+  case (TW_START): /* 0x08 : start condition transmitted */
+  case (TW_REP_START): /* 0x10 : repeated START condition transmitted */
+    twi_address();
+    twi_i = 0;
+    break;
+  case (TW_MT_ARB_LOST): /* 0x38 : arbitration lost in SLA+RW, SLA+R received, ACK returned */
+    break;
+    /* Master Transmitter */
+  case (TW_MT_SLA_ACK): /* 0x18 : SLA+W transmitted; ACK received */
+  case (TW_MT_SLA_NACK): /* 0x20 : SLA+W transmitted; NACK received */
+    TWDR = twi_transmit_buffer[0];
+    TWCR = (1 << TWEA) | (1 << TWEN) | (1 << TWIE) | (1 << TWINT);
+    twi_i++;
+    break;
+  case (TW_MT_DATA_ACK):/* 0x28 : data has been transmitted; ACK has been received */
+  case (TW_MT_DATA_NACK): /* 0x30 : data has been transmitted; NACK has been received */
+    if (twi_i == twi_nb_data_to_transmit)
+      {
+        if (twi_mode == WRITE)
+          {
+            twi_stop();
+            twi_flag_write_complete = 1;
+          }
+        else // READ
+          {
+            slave_address++;
+            twi_start();
+          }
+      }
+    else
+      {
+        twi_data(twi_transmit_buffer[twi_i]);
+        twi_i++;
+      }
+    break;
+    /* Master Receiver */
+  case (TW_MR_SLA_ACK):/* 0x40 : SLA+R has been transmitted; ACK has been received */
+  case (TW_MR_SLA_NACK): /* 0x48 : SLA+R has been transmitted; NACK has been received */
+    if (twi_nb_data_to_receive == 1)
+      {
+        TWCR &= ~(1 << TWEA); /* desactiver ACK pour la derniere demande */
+      }
+    break;
+  case (TW_MR_DATA_ACK):/* 0x50 : data received, ACK transmitted */
+  case (TW_MR_DATA_NACK): /* 0x58 : data received, NACK transmitted */
+    twi_receive_buffer[twi_i] = TWDR;
+    twi_i++;
+    if (twi_i == (twi_nb_data_to_receive - 1))
+      {
+        TWCR &= ~(1 << TWEA); /* desactiver ACK pour la derniere demande */
+      }
+    if (twi_i == twi_nb_data_to_receive)
+      {
+        twi_flag_read_complete = 1;
+        twi_stop();
+      }
+    break;
+  default:
+    break;
+    }
+  TWCR |= (1 << TWINT); // TWINT flag bit is cleared
 }
-void twiError(void)
+/*
+ * twi master setup
+ * SCLfreq = CPUfreq / (16 + 2 * TWBR * presc)
+ * */
+void
+twi_master_setup(void)
 {
+  PORTC = (1 << PC5) | (1 << PC4); // activate internal pull_ups for twi
+  TWSR = 0x00;    // no prescaler
+  TWBR = 72; // 100kHz @16Mhz
+  //TWBR = 0x0C;    // 400 KHz @16MHz
+  TWCR = (1 << TWEA) | (1 << TWEN) | (1 << TWIE) | (1 << TWINT);
+  SREG |= (1 << SREG_I);
 }
-void twiWait(unsigned char myStatus)
+void
+TWI_wait(void)
 {
-	while (!(TWCR & (1 << TWINT)))
+  while (!(TWCR & (1 << TWINT)))
-		;
+    ;
-	if ((TWSR & 0xF8) != myStatus)
-	{
-		twiError();
-	}
 }
-/* send START condition bit */
+/* transmit START condition */
-void twiStart(void)
+void
+twi_start(void)
 {
-	/* TWINT : TWI interrupt flag
+  TWCR = (1 << TWEA) | (1 << TWEN) | (1 << TWIE) | (1 << TWINT) | (1 << TWSTA); /* send start condition */
-	 * TWSTA : TWI START condition bit
-	 * TWSTO : TWI STOP condition bit
-	 * TWEN : TWI enable bit */
-	TWCR = (1 << TWINT) | (1 << TWSTA) | (0 << TWSTO) | (1 << TWEN);
-	twiWait(TW_START);
 }
-/* send slave address */
+/* transmit slave address SLA */
-void twiAddress(unsigned char myAddress)
+void
+twi_address(void)
 {
-	TWDR = myAddress;
+  TWDR = slave_address; /* load SLA into TWDR */
-	TWCR = (1 << TWINT) | (0 << TWSTA) | (0 << TWSTO) | (1 << TWEN);
-	twiWait(TW_MT_SLA_ACK); // 0x18, 0x20 or 0x38
+  TWCR &= ~(1 << TWSTA); /* desactivate START */
 }
-/* send data */
+/* transmit data */
-void twiData(unsigned char myData)
+void
+twi_data(uint8_t data)
 {
-	TWDR = myData;
+  TWDR = data;
-	TWCR = (1 << TWINT) | (0 << TWSTA) | (0 << TWSTO) | (1 << TWEN);
-	twiWait(TW_MT_DATA_ACK);
 }
-/* send STOP condition bit */
+/* transmit STOP condition */
-void twiStop(void)
+void
+twi_stop(void)
 {
-	TWCR = (1 << TWINT) | (0 << TWSTA) | (1 << TWSTO) | (1 << TWEN);
+  TWCR |= (1 << TWSTO); /* STOP */
 }
-/* write data to slaveAddress */
+void
-void twiWriteData(unsigned char slaveAddress, unsigned char data)
+twi_write_bytes(uint8_t add, uint8_t nb_bytes, volatile uint8_t *buffer)
 {
-	twiStart();
+  if (twi_flag_write_complete == 1)
-	twiAddress(slaveAddress);
+    {
-	twiData(data);
+      twi_flag_write_complete = 0;
-	twiStop();
+      slave_address = add << 1;
+      twi_transmit_buffer = buffer;
+      twi_start();
+    }
 }
+void
+twi_read_bytes(uint8_t add, volatile uint8_t *reg, uint8_t nb_bytes,
+    volatile uint8_t *buffer)
+{
+  if (twi_flag_read_complete == 1)
+    {
+      twi_flag_read_complete = 0;
+      twi_flag_write_complete = 0;
-int main(void)
+      slave_address = add;
+      twi_transmit_buffer = reg;
+      twi_mode = READ;
+      twi_nb_data_to_transmit = 1;
+      twi_nb_data_to_receive = nb_bytes;
+      twi_receive_buffer = buffer;
+      twi_start();
+      while (twi_flag_read_complete == 0)
+        ;
+    }
+}
+void
+setup(void)
 {
-	twiMasterInitialise(92, 0);	//set TWBR = 92 for 100kHz SCL @ 20MHz
+  twi_master_setup();
+}
-	while (1)
+int
-	{
+main(void)
-		twiWriteData(0x20, 0x05); //write 0x05 @0x20
+{
-	}
+  uint8_t * buf;
-	return 1;
+  setup();
+  while (1)
+    {
+      twi_read_bytes(0x68, 0x42, 1, buf);
+    }
 }
 </code>

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