Problem with Fleury TWI code

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My target device is an ATMega 168p with an external crystal at 16.384 Mhz. IDE is Atmel Studio 6 and GCC. Debugging with JTAGIce MKII and debugwire. I am attempting to use Peter Fleury's TWI code and am able to send a start and address byte. My slave device ACKS (verified with a logic analyzer). When I reach this line in i2c_start

	if ( (twst != TW_MT_SLA_ACK) && (twst != TW_MR_SLA_ACK) ) return 1;

I examine twst in the debugger and it equals 0x18 which is TW_MT_SLA_ACK the function returns failure rather than success. Here is the rest of the code.

/*
 * i2ctest.cpp
 */ 

#define F_CPU			16384000
#define TWI_READ_BIT	0 
#define PORT_PWR		PC1

#include 
#include 
#include 
#include 
#include 
#include "i2cmaster.h"

volatile uint8_t MsTick;
volatile uint16_t I2cCntr;
volatile uint8_t I2cTimeOut;
uint8_t I2cPacket[] = {1,2,3,4,5,6,7,8,9,0,1,2,3,4,5,6};
uint8_t I2cTarget = 0xe0;

void Timer_Init (void)
{
	//Timer0 is the 1ms tick
	//CTC mode
	//sysclk/256
	//interrupt occurs at 1 ms
	TCCR0A = (1<<WGM01);
	TCCR0B = (1<<CS02);
	OCR0A = 63;
	//Enable compare match interrupt
	TIMSK0 = (1<<OCIE0A);	
}

ISR (TIMER0_COMPA_vect)
{
	MsTick = true;
	I2cCntr++;
	I2cTimeOut++;
}

bool Packet_Write(void)
{
	uint8_t index;
	//power the device
	PORTC |= (1<<PORT_PWR);
	_delay_ms(10);
	
	//ensure the read bit is clear
	if(i2c_start(I2cTarget & ~(1<<TWI_READ_BIT)));
	{
		return false;
	}
	if(i2c_write(0x10));
	{
		return false;
	}
	for(index = 0;index < 16;index++)
	{
		if(i2c_write(I2cPacket
)); { return false; } } //send a stop i2c_stop(); return true; } int main(void) { DDRC = (1<<PORT_PWR); Timer_Init(); i2c_init(); sei(); while(1) { //send a packet every 900 ms if (I2cCntr >= 900) { I2cCntr = 0; Packet_Write(); PORTC &= ~(1<<PORT_PWR); } } }
#ifndef _I2CMASTER_H
#define _I2CMASTER_H   1
/************************************************************************* 
* Title:    C include file for the I2C master interface 
*           (i2cmaster.S or twimaster.c)
* Author:   Peter Fleury   http://jump.to/fleury
* File:     $Id: i2cmaster.h,v 1.10 2005/03/06 22:39:57 Peter Exp $
* Software: AVR-GCC 3.4.3 / avr-libc 1.2.3
* Target:   any AVR device
* Usage:    see Doxygen manual
**************************************************************************/

#ifdef DOXYGEN
/**
 @defgroup pfleury_ic2master I2C Master library
 @code #include  @endcode
  
 @brief I2C (TWI) Master Software Library

 Basic routines for communicating with I2C slave devices. This single master 
 implementation is limited to one bus master on the I2C bus. 

 This I2c library is implemented as a compact assembler software implementation of the I2C protocol 
 which runs on any AVR (i2cmaster.S) and as a TWI hardware interface for all AVR with built-in TWI hardware (twimaster.c).
 Since the API for these two implementations is exactly the same, an application can be linked either against the
 software I2C implementation or the hardware I2C implementation.

 Use 4.7k pull-up resistor on the SDA and SCL pin.
 
 Adapt the SCL and SDA port and pin definitions and eventually the delay routine in the module 
 i2cmaster.S to your target when using the software I2C implementation ! 
 
 Adjust the  CPU clock frequence F_CPU in twimaster.c or in the Makfile when using the TWI hardware implementaion.

 @note 
    The module i2cmaster.S is based on the Atmel Application Note AVR300, corrected and adapted 
    to GNU assembler and AVR-GCC C call interface.
    Replaced the incorrect quarter period delays found in AVR300 with 
    half period delays. 
    
 @author Peter Fleury pfleury@gmx.ch  http://jump.to/fleury

 @par API Usage Example
  The following code shows typical usage of this library, see example test_i2cmaster.c

 @code

 #include 


 #define Dev24C02  0xA2      // device address of EEPROM 24C02, see datasheet

 int main(void)
 {
     unsigned char ret;

     i2c_init();                             // initialize I2C library

     // write 0x75 to EEPROM address 5 (Byte Write) 
     i2c_start_wait(Dev24C02+I2C_WRITE);     // set device address and write mode
     i2c_write(0x05);                        // write address = 5
     i2c_write(0x75);                        // write value 0x75 to EEPROM
     i2c_stop();                             // set stop conditon = release bus


     // read previously written value back from EEPROM address 5 
     i2c_start_wait(Dev24C02+I2C_WRITE);     // set device address and write mode

     i2c_write(0x05);                        // write address = 5
     i2c_rep_start(Dev24C02+I2C_READ);       // set device address and read mode

     ret = i2c_readNak();                    // read one byte from EEPROM
     i2c_stop();

     for(;;);
 }
 @endcode

*/
#endif /* DOXYGEN */

/**@{*/

#if (__GNUC__ * 100 + __GNUC_MINOR__) < 304
#error "This library requires AVR-GCC 3.4 or later, update to newer AVR-GCC compiler !"
#endif

#include 

/** defines the data direction (reading from I2C device) in i2c_start(),i2c_rep_start() */
#define I2C_READ    1

/** defines the data direction (writing to I2C device) in i2c_start(),i2c_rep_start() */
#define I2C_WRITE   0


/**
 @brief initialize the I2C master interace. Need to be called only once 
 @param  void
 @return none
 */
extern void i2c_init(void);


/** 
 @brief Terminates the data transfer and releases the I2C bus 
 @param void
 @return none
 */
extern void i2c_stop(void);


/** 
 @brief Issues a start condition and sends address and transfer direction 
  
 @param    addr address and transfer direction of I2C device
 @retval   0   device accessible 
 @retval   1   failed to access device 
 */
extern unsigned char i2c_start(unsigned char addr);


/**
 @brief Issues a repeated start condition and sends address and transfer direction 

 @param   addr address and transfer direction of I2C device
 @retval  0 device accessible
 @retval  1 failed to access device
 */
extern unsigned char i2c_rep_start(unsigned char addr);


/**
 @brief Issues a start condition and sends address and transfer direction 
   
 If device is busy, use ack polling to wait until device ready 
 @param    addr address and transfer direction of I2C device
 @return   none
 */
extern void i2c_start_wait(unsigned char addr);

 
/**
 @brief Send one byte to I2C device
 @param    data  byte to be transfered
 @retval   0 write successful
 @retval   1 write failed
 */
extern unsigned char i2c_write(unsigned char data);


/**
 @brief    read one byte from the I2C device, request more data from device 
 @return   byte read from I2C device
 */
extern unsigned char i2c_readAck(void);

/**
 @brief    read one byte from the I2C device, read is followed by a stop condition 
 @return   byte read from I2C device
 */
extern unsigned char i2c_readNak(void);

/** 
 @brief    read one byte from the I2C device
 
 Implemented as a macro, which calls either i2c_readAck or i2c_readNak
 
 @param    ack 1 send ack, request more data from device
0 send nak, read is followed by a stop condition @return byte read from I2C device */ extern unsigned char i2c_read(unsigned char ack); #define i2c_read(ack) (ack) ? i2c_readAck() : i2c_readNak(); /**@}*/ #endif
/*************************************************************************
* Title:    I2C master library using hardware TWI interface
* Author:   Peter Fleury   http://jump.to/fleury
* File:     $Id: twimaster.c,v 1.3 2005/07/02 11:14:21 Peter Exp $
* Software: AVR-GCC 3.4.3 / avr-libc 1.2.3
* Target:   any AVR device with hardware TWI 
* Usage:    API compatible with I2C Software Library i2cmaster.h
**************************************************************************/
#include 
#include 

#include "i2cmaster.h"


/* define CPU frequency in Mhz here if not defined in Makefile */
#ifndef F_CPU
#define F_CPU 16384000UL
#endif

/* I2C clock in Hz */
#define SCL_CLOCK  100000L


/*************************************************************************
 Initialization of the I2C bus interface. Need to be called only once
*************************************************************************/
void i2c_init(void)
{
  /* initialize TWI clock: 100 kHz clock, TWPS = 0 => prescaler = 1 */
  
  TWSR = 0;                         /* no prescaler */
  TWBR = 235;

}/* i2c_init */


/*************************************************************************	
  Issues a start condition and sends address and transfer direction.
  return 0 = device accessible, 1= failed to access device
*************************************************************************/
unsigned char i2c_start(unsigned char address)
{
    uint8_t   twst;

	// send START condition
	TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);

	// wait until transmission completed
	while(!(TWCR & (1<<TWINT)));

	// check value of TWI Status Register. Mask prescaler bits.
	twst = TW_STATUS & 0xF8;
	if ( (twst != TW_START) && (twst != TW_REP_START)) return 1;

	// send device address
	TWDR = address;
	TWCR = (1<<TWINT) | (1<<TWEN);

	// wail until transmission completed and ACK/NACK has been received
	while(!(TWCR & (1<<TWINT)));

	// check value of TWI Status Register. Mask prescaler bits.
	twst = TW_STATUS & 0xF8;
	if ( (twst != TW_MT_SLA_ACK) && (twst != TW_MR_SLA_ACK) ) return 1;

	return 0;

}/* i2c_start */


/*************************************************************************
 Issues a start condition and sends address and transfer direction.
 If device is busy, use ack polling to wait until device is ready
 
 Input:   address and transfer direction of I2C device
*************************************************************************/
void i2c_start_wait(unsigned char address)
{
    uint8_t   twst;


    while ( 1 )
    {
	    // send START condition
	    TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);
    
    	// wait until transmission completed
    	while(!(TWCR & (1<<TWINT)));
    
    	// check value of TWI Status Register. Mask prescaler bits.
    	twst = TW_STATUS & 0xF8;
    	if ( (twst != TW_START) && (twst != TW_REP_START)) continue;
    
    	// send device address
    	TWDR = address;
    	TWCR = (1<<TWINT) | (1<<TWEN);
    
    	// wail until transmission completed
    	while(!(TWCR & (1<<TWINT)));
    
    	// check value of TWI Status Register. Mask prescaler bits.
    	twst = TW_STATUS & 0xF8;
    	if ( (twst == TW_MT_SLA_NACK )||(twst ==TW_MR_DATA_NACK) ) 
    	{    	    
    	    /* device busy, send stop condition to terminate write operation */
	        TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);
	        
	        // wait until stop condition is executed and bus released
	        while(TWCR & (1<<TWSTO));
	        
    	    continue;
    	}
    	//if( twst != TW_MT_SLA_ACK) return 1;
    	break;
     }

}/* i2c_start_wait */


/*************************************************************************
 Issues a repeated start condition and sends address and transfer direction 

 Input:   address and transfer direction of I2C device
 
 Return:  0 device accessible
          1 failed to access device
*************************************************************************/
unsigned char i2c_rep_start(unsigned char address)
{
    return i2c_start( address );

}/* i2c_rep_start */


/*************************************************************************
 Terminates the data transfer and releases the I2C bus
*************************************************************************/
void i2c_stop(void)
{
    /* send stop condition */
	TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);
	
	// wait until stop condition is executed and bus released
	while(TWCR & (1<<TWSTO));

}/* i2c_stop */


/*************************************************************************
  Send one byte to I2C device
  
  Input:    byte to be transfered
  Return:   0 write successful 
            1 write failed
*************************************************************************/
unsigned char i2c_write( unsigned char data )
{	
    uint8_t   twst;
    
	// send data to the previously addressed device
	TWDR = data;
	TWCR = (1<<TWINT) | (1<<TWEN);

	// wait until transmission completed
	while(!(TWCR & (1<<TWINT)));

	// check value of TWI Status Register. Mask prescaler bits
	twst = TW_STATUS & 0xF8;
	if( twst != TW_MT_DATA_ACK) return 1;
	return 0;

}/* i2c_write */


/*************************************************************************
 Read one byte from the I2C device, request more data from device 
 
 Return:  byte read from I2C device
*************************************************************************/
unsigned char i2c_readAck(void)
{
	TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWEA);
	while(!(TWCR & (1<<TWINT)));    

    return TWDR;

}/* i2c_readAck */


/*************************************************************************
 Read one byte from the I2C device, read is followed by a stop condition 
 
 Return:  byte read from I2C device
*************************************************************************/
unsigned char i2c_readNak(void)
{
	TWCR = (1<<TWINT) | (1<<TWEN);
	while(!(TWCR & (1<<TWINT)));
	
    return TWDR;

}/* i2c_readNak */
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Your TWBR is definitely not 100kHz bus.

I suspect that you have omitted 4k7 external pull-up resistors.

Personally, I would place F_CPU=16384000 in the AS6.1 Symbols or in a Makefile.

I really don't like dependence on people leaving these things to chance !

It also means that you never edit twimaster.c.
So the whole world knows you are using proven code.

Your Fleury calls look fine to me.
I have no intention of diffing your files with the official distribution. I suggest that you do that first.

Yes, you do need to edit i2c_master.S for your particular chip.
But ASM programmers are probably more careful.

David.

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Quote:
Your TWBR is definitely not 100kHz bus.
That is correct.
Quote:
I suspect that you have omitted 4k7 external pull-up resistors.
No. I haven't
Quote:
Personally, I would place F_CPU=16384000 in the AS6.1 Symbols or in a Makefile.
That is the way I did it in the actual program. This is an extract that demonstrates the problem.
Quote:
I really don't like dependence on people leaving these things to chance !
Not sure what you mean there.
Quote:
Yes, you do need to edit i2c_master.S for your particular chip.
As I understand it i2c_master.S is a bitbanged implementation for chips without the TWI interface.
Quote:
But ASM programmers are probably more careful.
I was an ASM programmer for about a decade before switching to C.
Interestingly my problem went awar after I modified the code to return the TW_STATUS value and test it in my Packet_Write() function.
uint8_t i2c_start(unsigned char address)
{
    uint8_t   twst;

	// send START condition
	TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);

	// wait until transmission completed
	while(!(TWCR & (1<<TWINT)));

	// check value of TWI Status Register. Mask prescaler bits.
	twst = TW_STATUS & 0xF8;
	if ( (twst != TW_START) && (twst != TW_REP_START)) 
		return 0;

	// send device address
	TWDR = address;
	TWCR = (1<<TWINT) | (1<<TWEN);

	// wail until transmission completed and ACK/NACK has been received
	while(!(TWCR & (1<<TWINT)));

	// check value of TWI Status Register. Mask prescaler bits.
	twst = TW_STATUS & 0xF8;
	return twst;
	/*if ( (twst != 0x18) && (twst != 0x40) ) 
		return 1;

	return 0;*/

}/* i2c_start */
unsigned char i2c_write( unsigned char data )
{	
    uint8_t   twst;
    
	// send data to the previously addressed device
	TWDR = data;
	TWCR = (1<<TWINT) | (1<<TWEN);

	// wait until transmission completed
	while(!(TWCR & (1<<TWINT)));

	// check value of TWI Status Register. Mask prescaler bits
	twst = TW_STATUS & 0xF8;
	return twst;
	/*if( twst != TW_MT_DATA_ACK) return 1;
	return 0;*/

}/* i2c_write */
bool Packet_Write(void)
{
	uint8_t index;
	//ensure the read bit is clear
	i2creturnvalue = i2c_start(I2cTarget & ~(1<<TWI_READ_BIT));
	if((i2creturnvalue != TW_MT_SLA_ACK)&&(i2creturnvalue != TW_MR_SLA_ACK))
	{
		return false;
	}
	i2creturnvalue = i2c_write(0x10);
	if( i2creturnvalue != TW_MT_DATA_ACK)	
	{
		return false;
	}
	for(index = 0;index < 16;index++)
	{
		i2creturnvalue = i2c_write(IkeyPacket_Enc
); if( i2creturnvalue != TW_MT_DATA_ACK) { return false; } } //send a stop i2c_stop(); return true; }

This however brings me to the reason that I switched to the Fleury code in the first place. If I do a read all works well if I read 17 bytes or less. If I try to read 18 bytes rather than terminating at the last byte with a NAK and STOP I get an ACK and no STOP. Here is my read code

bool Packet_Read(void)
{
	uint8_t index;
	//ensure the read bit is set
	i2creturnvalue = i2c_start(I2cTarget | (1<<TWI_READ_BIT));
	if((i2creturnvalue != TW_MT_SLA_ACK)&&(i2creturnvalue != TW_MR_SLA_ACK))
	{
		return false;
	}
	//first byte is 0x10 discard it
	i2creturnvalue = i2c_readAck();
	//get the packet
	//if limit is set to 15 all works fine
	//if limit is set to 16 no NAK or STOP
	for(index = 0;index < 15;index++)
	{
		
		IkeyPacket_Enc
= i2c_readAck(); } //read and discard one more byte and nack i2c_readNak(); //send a stop i2c_stop(); return true; }
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Yes, i2c_master.S is the bit-banged version. Not relevant here, but I just mentioned that you need to edit before use.

The C files require no editing.

Yes, I prefer to return TWSTATUS as GOOD and 0 as BAD.
However, Fleury's convention is an equally good approach.

Why have you hard-coded a non-standard bus speed ?

Personally, I would start afresh with the Fleury distribution.
Set F_CPU in Symbols.
Measure the 4k7 pull-up resistors with a multimeter.

If you still have a problem, ask again.

Which I2C chip are you talking too?

David.

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What I'm talking to is an electronic key for a security system. The key has a Microchip processor. It is a legacy device and can't be changed due to compatibility with other products. The non-standard bus speed is part of the protocol that I need to comply with. This is a firmware upgrade of an existing product with about 10,000 units in the field so I'm pretty sure the pullup resistors are OK.

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Well, M*crochip's I2C works just fine. (if you use it as intended)

Of course, if it is deliberately misused for 'security' purposes, the gloves are off.

You can measure the pull-up resistors without accessing the pcb. Just place a milliammeter between SDA and GND. I would expect 4mA or so.

An alternative is to observe the SCL line with an oscilloscope.
This will reveal the bus capacitance from the risetime.

Having determined the R and C by the above methods, you can determine whether the I2C bus is 'legal' or deliberately misused.

Just sniff the good transactions with a Logic Analyser. I2C is very straightforward to use.

However, you appear to read a dummy readAck, 15 readAcks and a dummy readNak. 'Normal' transactions would be 15 readAck + final readNak giving you 16 bytes of data.

David.

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Quote:
However, you appear to read a dummy readAck, 15 readAcks and a dummy readNak. 'Normal' transactions would be 15 readAck + final readNak giving you 16 bytes of data.
Like I said it's deliberately non standard. Everything works now after I tuned optimizations off temporarily for debugging. After I reenabled them all works great. I figure that forced a clean rebuild.

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I know you just got it working, but for future reference, there's also a TWI library on Atmel Spaces:
http://spaces.atmel.com/gf/proje...

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Interesting. I haven't see that site before. Is it new?

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Quote:

Is it new?

First mentioned October 2012:

https://www.avrfreaks.net/index.p...