AVR Freaks

Thanks for replying!

I'm using the internal oscillator, configured at 8MHz: Int. RC Osc. 8 MHz; Start-up time PWRDWN/RESET: 6 CK/14CK + 65ms INTRCOSC_8MHZ_6CK_14CK_65MS

The LOW.CKDIV8 fuse was indeed set -- perhaps this is default? Clearing it, and the communications look a lot better, but still not perfect.

Where the ATMEGA16 would "achieve" perfect comms at 115200 baud, I'm currently receiving something like this (if I re-run/reset the avr):

USART_SendString("HEI VELKOMMEN VERDEN");

HEI VELKOMMEN VERDEN

HEI VELKOMMEN VERDEN

HEI VELKOMMEN VERDEN

HEI VELKOMMEN VERDEN
HEI VELKOMMEN VERDEN

HEI VELKOMMEN VERDEN

HEI VELKOMMEN VERDEN

HEI VELKOMMEN VERDEN
HEI VELKOMMEN VERDEN

HEI VELKOMMEN VERDEN

ÈÅI ÖÅÌËÏÍMÅÎ ÖEÒÄÅN

HEI VELKOMMEN VERÄEN
HEI VELKOMMEN VERDEN

HEI VELKOMMEN VÃ…RDEN

Is there reason to expect different "performance" of the internal clock of an ATMEGA88 than that of an ATMEGA16? 

I guess I should use an external crystal, but I'd hope to understand more of this problem while I'm at it.

Here are the fuses as set:

Joakim

Currently, I have the on board oscillator set to 3.686MHz, with the STK jumpers mounted to default settings:

Does this mean the ATMEGA88 (and the ATMEGA16, for that matter) is clocked at 3.686MHz, and not to the 8MHz I'm trying to configure in the software?

I'm still struggling to port my code from ATMEGA16 to AMTEGA88. Adapting the code (as described earlier/above) proves to be complicated, especially so when I can never be sure if the serial comms is not working due to improper clocking. I have tried to compare the datasheets to get the UART setup (registers) correct --- mostly, the register names are the same but with an extra "0" appended to them:

Meanwhile, I have ordered some crystals from Digikey, and now have a bag of 3.6864 MHz (and 9.2160MHz), but then I'm facing problems understanding how to hook up an external crystal in the STK500 properly. Reading the STK manual, it seems I should simply plug the crystal in the socket, and change the OSCSEL and XTAL1 jumpers, but then I also need to change a fuse in the ATMEGA88 (the LOW.SUT_CKSEL fuse), which is currently set to "Int. RC Osc. 8 MHz)? As in my previous question, are the prescaler calculations the same as for 8MHz?

Here's what happens when I try to change the fuse to some external crystal setting. Programming (setting) the fuse seems to go OK (the yellow ! icon on LOW.SUT_CKSEL in the above screenshot turns into a green check) but after that the chips is toast.

It does not run, and I'm unable to re-program the fuses using Atmel Studio:

But the fuse setting was "Ext. Low-Freq. Crystal"...

The crystal I'm using is 3.6864MHz -- I have no idea if this is low or high frequency?

I did, however, manage to set the fuses correctly (it didn't brick, at least) by using an online fuse calculator: http://www.engbedded.com/fusecalc

By guessing "Ext. Full-swing crystal" (again, crystal), and un-checking CKDIV8, it output: 

Low: 0xC6

High: 0xDF

Extended: 0xF9

Entering these hex values in the Fuses dialog of Atmel Studio, I was able to program (a new) ATMEGA88-20PU. Yet, I'm in no way confident these are correct settings?

It's been a long thread, so I hope a brief repetition is OK: I want to set up the ATMEGA88's UART for 115200 baud, 8n1.

The terminal program now only displays "junk bytes"...

Are these baud prescaler calculations still proper?

#define F_CPU 3686400UL					/* Define CPU clock Frequency */
#include <avr/io.h>							/* Include AVR std. library file */
#include <math.h>

//#define DOUBLE_SPEED_MODE

#ifdef DOUBLE_SPEED_MODE
	#define BAUD_PRESCALE (int)round(((((double)F_CPU / ((double)BAUDRATE * 8UL))) - 1UL))	/* Define prescale value */
#else
	#define BAUD_PRESCALE (int)round(((((double)F_CPU / ((double)BAUDRATE * 16UL))) - 1UL))	/* Define prescale value */
#endif

and here is my registers setup for the UART:

void USART_Init(unsigned long BAUDRATE)				/* USART initialize function */
{
#ifdef DOUBLE_SPEED_MODE
	UCSR0A |=(1 << U2X0);
#endif
	UCSR0B |= (1 << RXEN0) | (1 << TXEN0);	/* Enable USART transmitter and receiver */
	UCSR0C |= (1<<USBS0)| (1 << UCSZ00 ) | (1 << UCSZ01 );	/* Write USCRC for 8 bit data and 1 stop bit */ 
	UBRR0L = BAUD_PRESCALE;							/* Load UBRRL with lower 8 bit of prescale value */
	UBRR0H = (BAUD_PRESCALE >> 8);					/* Load UBRRH with upper 8 bit of prescale value */
	UCSR0B |= (1 << RXCIE0 );
}

OK, finally, this seems to have converged to something stable :D

Setting high-freq crystal, as below, does not brick the AVR and the program seems to run as intended!

Furthermore, the UART is now communicating reliably with the ESP8266 -- just like the ATMEGA16 did.

So it seems I'm back on track, having ported from ATMEGA16 to ATMEGA88. Thanks for all the help and guidance, everyone!