AVR Freaks

Thank you for the replies, everyone! Sounds like I've got some exciting days ahead of me either finding an XMEGA i2c lib or writing my own i2c library (*shudders*). 

Out of curiosity, any ideas on why the T817 seems like a tiny/mega hybrid? 

If it helps, here is the Build output from Atmel Studio: 

------ Build started: Project: headphones, Configuration: Debug AVR ------
Build started.
Project "headphones.cproj" (default targets):
Target "PreBuildEvent" skipped, due to false condition; ('$(PreBuildEvent)'!='') was evaluated as (''!='').
Target "CoreBuild" in file "C:\Program Files (x86)\Atmel\Studio\7.0\Vs\Compiler.targets" from project "C:\Users\Mike\Documents\Atmel Studio\7.0\headphones\headphones\headphones.cproj" (target "Build" depends on it):
    Task "RunCompilerTask"
        Shell Utils Path C:\Program Files (x86)\Atmel\Studio\7.0\shellUtils
        C:\Program Files (x86)\Atmel\Studio\7.0\shellUtils\make.exe all --jobs 4 --output-sync 
        Building file: .././twi_master_driver.c
        Invoking: AVR/GNU C Compiler : 4.9.2
        "C:\Program Files (x86)\Atmel\Studio\7.0\toolchain\avr8\avr8-gnu-toolchain\bin\avr-gcc.exe"  -x c -funsigned-char -funsigned-bitfields -DDEBUG  -I"C:\Program Files (x86)\Atmel\Studio\7.0\Packs\atmel\ATtiny_DFP\1.1.102\include"  -O1 -ffunction-sections -fdata-sections -fpack-struct -fshort-enums -g2 -Wall -mmcu=attiny817 -B "C:\Program Files (x86)\Atmel\Studio\7.0\Packs\atmel\ATtiny_DFP\1.1.102\gcc\dev\attiny817" -c -std=gnu99 -MD -MP -MF "twi_master_driver.d" -MT"twi_master_driver.d" -MT"twi_master_driver.o"   -o "twi_master_driver.o" ".././twi_master_driver.c" 
        Finished building: .././twi_master_driver.c
        Building file: .././main.c
        Invoking: AVR/GNU C Compiler : 4.9.2
        "C:\Program Files (x86)\Atmel\Studio\7.0\toolchain\avr8\avr8-gnu-toolchain\bin\avr-gcc.exe"  -x c -funsigned-char -funsigned-bitfields -DDEBUG  -I"C:\Program Files (x86)\Atmel\Studio\7.0\Packs\atmel\ATtiny_DFP\1.1.102\include"  -O1 -ffunction-sections -fdata-sections -fpack-struct -fshort-enums -g2 -Wall -mmcu=attiny817 -B "C:\Program Files (x86)\Atmel\Studio\7.0\Packs\atmel\ATtiny_DFP\1.1.102\gcc\dev\attiny817" -c -std=gnu99 -MD -MP -MF "main.d" -MT"main.d" -MT"main.o"   -o "main.o" ".././main.c" 
        Finished building: .././main.c
        Building target: headphones.elf
        Invoking: AVR/GNU Linker : 4.9.2
        "C:\Program Files (x86)\Atmel\Studio\7.0\toolchain\avr8\avr8-gnu-toolchain\bin\avr-gcc.exe" -o headphones.elf  main.o twi_master_driver.o   -Wl,-Map="headphones.map" -Wl,--start-group -Wl,-lm  -Wl,--end-group -Wl,--gc-sections -mmcu=attiny817 -B "C:\Program Files (x86)\Atmel\Studio\7.0\Packs\atmel\ATtiny_DFP\1.1.102\gcc\dev\attiny817"  
        Finished building target: headphones.elf
        "C:\Program Files (x86)\Atmel\Studio\7.0\toolchain\avr8\avr8-gnu-toolchain\bin\avr-objcopy.exe" -O ihex -R .eeprom -R .fuse -R .lock -R .signature -R .user_signatures  "headphones.elf" "headphones.hex"
        "C:\Program Files (x86)\Atmel\Studio\7.0\toolchain\avr8\avr8-gnu-toolchain\bin\avr-objcopy.exe" -j .eeprom  --set-section-flags=.eeprom=alloc,load --change-section-lma .eeprom=0  --no-change-warnings -O ihex "headphones.elf" "headphones.eep" || exit 0
        "C:\Program Files (x86)\Atmel\Studio\7.0\toolchain\avr8\avr8-gnu-toolchain\bin\avr-objdump.exe" -h -S "headphones.elf" > "headphones.lss"
        "C:\Program Files (x86)\Atmel\Studio\7.0\toolchain\avr8\avr8-gnu-toolchain\bin\avr-objcopy.exe" -O srec -R .eeprom -R .fuse -R .lock -R .signature -R .user_signatures "headphones.elf" "headphones.srec"
        "C:\Program Files (x86)\Atmel\Studio\7.0\toolchain\avr8\avr8-gnu-toolchain\bin\avr-size.exe" "headphones.elf"
           text       data        bss        dec        hex    filename
            310          0          0        310        136    headphones.elf
    Done executing task "RunCompilerTask".
    Using "RunOutputFileVerifyTask" task from assembly "C:\Program Files (x86)\Atmel\Studio\7.0\Extensions\Application\AvrGCC.dll".
    Task "RunOutputFileVerifyTask"
                Program Memory Usage     :    310 bytes   3.8 % Full
                Data Memory Usage         :    0 bytes   0.0 % Full
    Done executing task "RunOutputFileVerifyTask".
Done building target "CoreBuild" in project "headphones.cproj".
Target "PostBuildEvent" skipped, due to false condition; ('$(PostBuildEvent)' != '') was evaluated as ('' != '').
Target "Build" in file "C:\Program Files (x86)\Atmel\Studio\7.0\Vs\Avr.common.targets" from project "C:\Users\Mike\Documents\Atmel Studio\7.0\headphones\headphones\headphones.cproj" (entry point):
Done building target "Build" in project "headphones.cproj".
Done building project "headphones.cproj".

Build succeeded.
========== Build: 1 succeeded or up-to-date, 0 failed, 0 skipped ==========

Ok, I've fixed my previous problems and actually got my code to compile. However, the pins that I think should be the SDA and SCL for the TWI module are not outputting anything. I've attached my code, which right now is just a main.c file. I've read many times through relevant parts of the ATtiny817's datasheet (TWI, IO Pin Setup) and I would say that I am about 50% confident that I am initializing and using the TWI module correctly. I haven't implemented anything with interrupts yet, as I wanted to check the base functionality of my TWI 'library' before fully committing to interrupts. I would greatly appreciate it if someone that has experience with TWI on other boards would be able to look through my code and hazard a guess as to where I might be going wrong. Thank you!

Okay, that would be great. Thank you. 

Also, the example project uses the equation (F_CPU/(2*F_SCL) - 5) (found in the at30tse75x.c file) for calculating the baud rate to feed into the TWI_MasterInit function. However that is not the baud rate calculation found in the datasheet. According to the ATtiny817 datasheet, that equation (rearranging the f_SCL equation found on page 395) should be BAUD = ((F_CPU/F_SCL)-10-F_CPU*T_RISE)/2. I'm assuming the datasheet equation should be right, so why the inconsistency in the at30tse75x.c equation? Can the F_CPU*T_RISE term be neglected? 

I'm interfacing with a Sparkfun magnetometer breakout board that has 4.7k pullup resistors on the SCL and SDA lines on its end.

I am writing to the alternate pin function register to enable PA1 and PA2 being used for the TWI pins. I'm doing this because I'm also using the ATtiny for UART communication with a bluetooth module and PB1 and PB0 are used for XCK and XDIR for the USART0. Although this brings up a question: I'm not actually using XCK and XDIR for UART communication, but I assumed that if I enable the USART0 communication, those pins would automatically be assigned to XCK and XDIR functions. Can I overwrite those pins and use them instead as TWI pins? I just wasn't sure what would happen if you had two modules that were enabled and used some of the same pins. 

Update: I got the TWI communication working (kind of) using the PB1 and PB0 pins (although I didn't have the USART0 module enabled so we'll see what happens when I add that in). My code is structured in the following way:

1-Write several initialization values to magnetometer

2-Main loop:

    a. Write to magnetometer, requesting data from reg 0x5

    b. Read data from magnetometer

    c. Write to magnetometer, requesting data from reg 0x6

    d. Read data from magnetometer

    e. Perform processing on data

So far, I've determined (using a logic analyzer) that the initialization process (1) and the first request for data (2a) are being sent from the ATtiny817 and being acknowledged by the magnetometer. However, the first data read (2b) never happens. The logic analyzer shows that the first request for data just keeps repeating, as if there's some event that needs to happen to allow it to move on to the data read (2b). I've looked through the twi_master.c code and don't think I've missed anything. Can anyone help me pinpoint what could be happening here?  I've copy-pasted my code below.

#define F_CPU 3330000UL

#include <avr/io.h>
#include <avr/interrupt.h>
#include <stdio.h>
#include <stdlib.h>
#include <util/delay.h>
#include <atmel_start.h>
#include <twi_master.h>

#define MAG_ADDR 0x0E
#define F_CPU 3330000UL
#define CPU_SPEED 3330000
#define BAUDRATE 100000
#define true 1
#define false 0

/* TWI Master */
TWI_Master_t twi_master;
TWI_t inst;

void init_MAG(void){
    uint8_t data[2];
    data[0] = 0x11;
    data[1] = 0x80;
    
    TWI_MasterWrite(&twi_master, MAG_ADDR, data, 2);
    
    _delay_ms(15);

    data[0] = 0x10;
    data[1] = 0x01;
    
    TWI_MasterWrite(&twi_master, MAG_ADDR, data, 2);
}

volatile uint8_t readReg(uint8_t regAddr){
    volatile uint8_t data = 0;
    volatile uint8_t result = 0;
    uint8_t array[1];
    array[0] = regAddr;
    TWI_MasterWrite(&twi_master, MAG_ADDR, array, 1);
    
    _delay_us(5); //delay 5 microseconds
    
    result = TWI_MasterRead(&twi_master, MAG_ADDR, 1);
    
    if(result == true){
        data = twi_master.readData[0];
    }
    
    return data;
}

volatile uint16_t readMagValue(uint8_t msb_reg, uint8_t lsb_reg){
    volatile uint16_t val_low = 0;
    volatile uint16_t val_high = 0;
    volatile uint16_t out_val = 0;
    
    val_high =     readReg(msb_reg);
    
    //_delay_us(2); //delay 2 microseconds
    
    val_low = readReg(lsb_reg);
    
    out_val = (val_low | (val_high << 8));
    return out_val;
}

//Read z-axis magnetometer data
volatile uint16_t read_z(void){
    return readMagValue(0x05, 0x06); //z-axis data is in mag registers 0x05, 0x06
}

int main(void)
{
    volatile uint8_t result = 0;
    inst = TWI0;
    
    //PORTMUX.CTRLB |= PORTMUX_TWI0_ALTERNATE_gc;
    volatile uint8_t baud_rate = (CPU_SPEED/(2*BAUDRATE) - 5);
     
    TWI_MasterInit(&twi_master, &TWI0, (TWI_RIEN_bm | TWI_WIEN_bm), baud_rate);
    
    sei(); 
    
    init_MAG();
    
    while (1) 
    {
        result = read_z();
        
        if(result > 1000){
            PORTC.OUTSET |= (1<<0);
        }
        else{
            PORTC.OUTCLR |= (1<<0);
        }
        
        _delay_ms(100);
    }
}

ISR(TWI0_TWIM_vect)
{
    /* Needed for the TWI to complete transactions */
    TWI_MasterInterruptHandler(&twi_master);
}