Thomas33:
I will post the final code, just to make sure that I haven't overseen anything, but it may take a few days until I can split of some time again.
Well - it took more than a month now - but as I promised: Here is the code. Unfortunately there is one compile error left, but i am sure some of you guys will help me out of that 
ADDED: The error is:
RS_Heartbeat.cpp: In function 'void __vector_17()':
RS_Heartbeat:97: error: redefinition of 'void __vector_17()'
RS_Heartbeat:53: error: 'void __vector_17()' previously defined here
/*
roboshock heartbeat server
- receives data from ethernet and sends it out via serial
- requests data from serial all 20 ms and sends the response out via ethernet.
If receving certain chars from ethernet at the beginning of a new string
it takes special actions (and does not send such chars to serial)
created 2012
by Thomas Schuett
*/
// #define FASTADC 1
// defines for setting and clearing register bits
#ifndef cbi
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#endif
#ifndef sbi
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#endif
#include <SPI.h>
#include <Ethernet.h>
// #include "TimerOne.h"
// Enter a MAC address and IP address for your controller below.
// The IP address will be dependent on your local network:
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
byte ip[] = { 192,168,0, 111 };
//byte gateway[] = {192,168,0,1};
//byte subnet[] = { 255, 255, 255, 0 };
volatile boolean fired = false;
int TIME_FOR_ONE_CMD = 10; // in ms, starting conservative, depends on bautrate, includes time for sending to eth
long startTime = 0;
// ethernet send data must be buffered, to let it all go into one ethernet packet
char buffer[200];
int instructions_sent = 0;
int left_time = 0;
// Initialize the Ethernet server library
// with the IP address and port you want to use
// (port 80 is default for HTTP):
Server server(80);
Client client;
ISR(TIMER1_COMPA_vect)
{
fired = true;
}
void setup()
{
// from the forum:
#if FASTADC
// set prescale to 16, speeds up analogRead by around 0.1 ms per read
sbi(ADCSRA,ADPS2) ;
cbi(ADCSRA,ADPS1) ;
cbi(ADCSRA,ADPS0) ;
#endif
buffer[0] = 0;
// start the Ethernet connection and the server:
Ethernet.begin(mac, ip);
server.begin();
delay(1000);
blink();
Serial.begin(9600);
Serial2.begin(9600);
// Timer3.initialize(500000); // initialize timer1, and set a 1/2 second period
// Timer3.pwm(9, 512); // setup pwm on pin 9, 50% duty cycle
// Timer3.attachInterrupt(callback); // attaches callback() as a timer overflow interrupt
//Timer1::setMode (4, Timer1::PRESCALE_8, Timer1::NO_PORT);
// CTC mode with clk/8 prescaler
TCCR1A = 0;
TCCR1B = 1<<WGM12 | 1<<CS11;
TCNT1 = 0; // reset counter
OCR1A = 39999; // compare A register value
TIFR1 |= _BV (OCF1A); // clear interrupt flag
TIMSK1 = _BV (OCIE1A); // interrupt on Compare A Match
}
SIGNAL (TIMER1_COMPA_vect)
{
// handle_interrupts(_timer5, &TCNT5, &OCR5A);
// not needed in CTC mode: TCNT1 = 0; // reset the timer
fired = true;
TIFR1 = 1<<OCF1A; // clear the Output Compare A Match Flag
}
// ================================================================================
void loop()
{
if (fired)
{
fired = false;
startTime = millis();
// we want to use the same connection over and over
if (! client || ! client.connected()) {
client = server.available();
}
if (! client || ! client.connected()) {
return;
}
request_analog_from_serial();
instructions_sent = 0;
if (time_left() > TIME_FOR_ONE_CMD) {
if (forward_one_instruction_from_ethernet())
instructions_sent++;
}
if (time_left() > TIME_FOR_ONE_CMD) {
if (forward_one_instruction_from_ethernet())
instructions_sent++;
}
if (fired) {
// bad_timing ...
left_time= -1;
}
else {
// check_time_left ...
left_time= time_left();
}
sprintf(buffer+strlen(buffer),"Commands sent=%d\n", instructions_sent);
sprintf(buffer+strlen(buffer),"Time left=%d\n", left_time);
bufferToEthernet();
}
} // end of loop
long time_left() {
long now = millis();
return (20 - (now - startTime));
}
boolean forward_one_instruction_from_ethernet() {
if (! client.available()) { return false; }
char c = client.read();
if (c == 'V') { // needs 10 to 11 ms for all 16 analogValues :-)
char a[170];
a[0]=0;
for (int analogChannel = 0; analogChannel < 16; analogChannel++) {
sprintf(a+strlen(a),"a%02d=%d\n",
analogChannel,analogRead(analogChannel));
}
client.write(a);
client.println("END.");
}
else if (c == 'X') {
return false;
}
else if (c == 'H') {
Serial2.begin(38400);
}
else if (c == 'L') {
Serial2.begin(9600);
}
else {
while (c != '\n') {
Serial.print(c);
Serial2.print(c);
while (! client.available()) {
}
c = client.read();
}
Serial2.print("\r"); // !!! \r !!!
Serial.print("\n");
}
return true;
}
void request_analog_from_serial() {
Serial2.print("5a\r\n");
serialToBuffer();
}
void serialToBuffer() {
int i;
// have a timeout
long start = millis();
while (true) {
if (Serial2.available()) {
i = strlen(buffer);
char c2 = Serial2.read();
buffer[i] = c2;
buffer[i+1] = 0;
if (c2 == '\n') {
return;
}
}
long now = millis();
if ((now - start) > 100) {
buffer[i] = 0;
return;
}
if (strlen(buffer) > 168) {
return;
}
}
}
boolean bufferToEthernet() {
if (client.connected()) {
client.write(buffer);
buffer[0] = 0;
return true;
}
return false;
}
void blink() {
digitalWrite(13, HIGH); // set the LED on
delay(200); // wait for a second
digitalWrite(13, LOW); // set the LED off
delay(500); // wait for a second
}
void blink2() {
digitalWrite(13, HIGH); // set the LED on
delay(100); // wait for a second
digitalWrite(13, LOW); // set the LED off
delay(100); // wait for a second
}
If you have any remarks on the code, please feel free to mention it.
And if you want to know, for what all this shall be good for, you are welcome to visit my (recently ennewed) project page at roboshock.de