AVR Freaks

Well Mr. Moe123,

first, this helpful instructive code does not just show the initialization and second, it would be nice if you could offer specific help on the subject here.

Your objections, however, do not make much hope , or?

What should the sensor provide with these data?

Where do you set the address to read from? For that matter, what is the slave device? There is no mention of it in your code.

Hello, sir.

I am on the totally same kind of project now.

If you don't mind, please let me refer to your full code.

I don't want you to think I'm rude because of my short english.

Thank you.

Thank you. I thought I had something wrong in the code and thought it best to just delete the post, but I verified it was correct so I will post again.

The code below is just a starting point and is also minimal, but it does work (should work for any avr0/1). It is a master-only/polled/simplified version rewritten in C from what I have in C++. In this case tested on a tiny3217 with an lcd and a temp sensor, but any avr0/1 will do. It may or may not be easier to decipher than an atmel start version, but I would like to think it is.

Not complete, but a good start for simple reading/writing.  Contrary to what the datasheet describes (smart mode simplifies code and minimizes user interaction), I think smart mode can be left unused as these mcu's have no dma. In smart mode you have to set the NACK before the last read, in normal mode you just ACKread after each read (and NACKstop after done reading), so it amounts to just doing one thing (check if last byte, set to NACK) or the other (ACKread) in the read loop and there seems to be no advantage to smart mode that I can see. I suspect they are thinking of a dma capable mcu where a dma read would then do the ack when the dma transfer/read takes place. If there is something good about smart mode, anyone can correct me.

The reads/writes below can be 'chained' by specifying 'false' for the doStop argument, and the next read/write will end up being a repeated start. For both the read and write, the first buffer byte has to be the (unshifted) slave address. Check for the return value, if less than you planned then an error or nack occurred.

There are things missing (like slave, irq's), but should be good enough to talk to relatively simple/small data things that do not need irq's to move data or respond to other masters.

//Twi.h header avr0/1

#include <stdint.h>

#include <stdbool.h>

#define U8 uint8_t

void Twi_baudReg    (U8 v);

void Twi_on         ();

U8   Twi_readBytes  (U8* buf, const U8 len, bool doStop);

U8   Twi_writeBytes (const U8* buf, const U8 len, bool doStop);

#undef U8

//Twi.c avr0/1

#include <avr/io.h>

#include <stdint.h>

#include <stdbool.h>

#include "Twi.h"

#define U8 uint8_t

bool isAnyFlag      ()      { return TWI0.MSTATUS & 0b11101100; } //rif,wif,hold,arblost,buserr
bool isAnyErrFlag   ()      { return TWI0.MSTATUS & 0b00001100; } //arblost,buserr
void clearErrFlags  ()      { TWI0.MSTATUS = 0b00001100; } //arblost,buserr
void addressRead    (U8 v)  { TWI0.MADDR = (v<<1) | 1; }
void addressWrite   (U8 v)  { TWI0.MADDR = v<<1; }
void dataWR         (U8 v)  { TWI0.MDATA = v; }
U8   dataRD         ()      { return TWI0.MDATA; }
void Twi_baudReg    (U8 v)  { TWI0.MBAUD = v; }
void toStateIdle    ()      { TWI0.MSTATUS = 0b11101101; } //clear all flags, IDLE
void NACKstop       ()      { TWI0.MCTRLB = 0b0111; } //NACK,stop
void stop           ()      { TWI0.MCTRLB = 0b0011; } //ACK,stop
void ackActionACK   ()      { TWI0.MCTRLB = 0b0000; } //ACk,no cmd
void ACKread        ()      { TWI0.MCTRLB = 0b0010; } //ACK,read
bool isWriteOK      ()      { return TWI0.MSTATUS == 0b01100010; } //wif,hold,rxack=0,owner = ok
bool isReadOK       ()      { return TWI0.MSTATUS == 0b10100010; } //rif,hold,rxack=0(from a previous write ack),owner = ok
void Twi_on         ()      { toStateIdle(); TWI0.MCTRLA = 1; }

//can make timeout whatever value you want, is 256 clks in this case

bool waitTimeout () {
    U8 t = 0;
    while( ++t && !isAnyFlag() );
    return t != 0; //if t==0, is timeout, t!=0 is any flag set
}

//if any error flags, just clear error flags, else send stop
void anyFail () {
    if( isAnyErrFlag() ) clearErrFlags(); //or toStateIdle() if want to force state
    else stop();
}

bool waitWriteOK () {
    if( waitTimeout() && isWriteOK() ) return true;
    anyFail();
    return false;
}

bool waitReadOK () {
    if( waitTimeout() && isReadOK() ) return true;
    anyFail();
    return false;
}

// buf[0] = address, len = bytes to read into buf, doStop = true = stop when done
// return bytes read
U8 Twi_readBytes (U8* buf, const U8 len, bool doStop) {
    U8 readLen = 0;
    ackActionACK();                            //we ack reads
    addressRead(*buf);                         //start, ack, read 1 byte

    //if was ok, we already have 1 byte
    while( true ){
        if( ! waitReadOK() ) return readLen;   //error?
        *buf++ = dataRD();                     //store data
        if( ++readLen >= len ) break;          //done?
        ACKread();                             //allow read next byte
    }
    if( doStop ) NACKstop();                   //send stop? (also NACK last read)
    return readLen;
}

// buf[0] = address, len = bytes to write from buf, doStop = true = stop when done
// return bytes written (including address)
U8 Twi_writeBytes (const U8* buf, const U8 len, bool doStop) {
    U8 writeLen = 0;
    addressWrite(*buf++);                        //start
    while( true ){
        if( ! waitWriteOK() ) return writeLen;   //error? (or NACK)
        if( ++writeLen >= len ) break;           //more?
        dataWR(*buf++);                          //send next byte
    }
    if( doStop ) stop();                         //send stop?
    return writeLen;
}

#undef U8

//end Twi.c

/*

twi baud - too fast is not ok, too slow is ok
the typical maximum value for baud register will be 95 - (20MHz cpu clk, 100kHz scl)
so use 95 if you don't want to do any thinking (will be slower than 100kHz)
you can also eliminate rise time in calculations (probably unknown), 
  will just end up being a little slower than ideal

pins- use portmux if want to use the alternate pins

pins- the twi takes over the pins completely so nothing to do to set them up (even overrides inputdisable)

EXAMPLE

read ID register (2 bytes) of TMP117
write 15 to set pointer to ID register
then read 2 bytes

remember readBytes needs an address in the first byte of the buffer

in this case we are reusing the write buffer so address is already in place

*/

#include "Twi.h"

#include <stdint.h>

int main(){

Twi_baudReg( 95 );                         //100kHz@20MHz, 50kHz@10Mhz, etc.
Twi_on();                                  //to IDLE, enable

const uint8_t addr = 0x48;                 //TMP117 address
uint16_t id = 0;
uint8_t buf[2] = { addr, 15 };             //use same buffer for write and read in this case
if( 2 == Twi_writeBytes(buf, 2, false) &&  //no stop, so read will
    2 == Twi_readBytes(buf, 2, true) ) {   //be a repeat start
    id = (buf[0]<<8) | buf[1];             //big endian to little endian

    //id was read ok
}

}

edit- changed a couple C++ things found, like 'not' to !

In an online compiler (for mega4809, as that is the only avr0/1 io.h info they have it seems, but is the same code)

https://godbolt.org/z/k-BP66

a little simpler, where readBytes/writeBytes just returns true/false (not really going to make use of bytes read/written if not what we wanted, so true/false is fine)

https://godbolt.org/z/7jDe4i