Valid baud rates for Duemilanove clone

Using Arduino Programming Questions
1

I'm having a Duemilanove clone with an pl2303hx chip for usb communication.

Which are valid baud rates for that chip in the Arduino IDE and on Linux? I need baud rates >= 500000, but only can get it working through 230400 (or i receive crap). The chip should support baud rates up to 6M.

Thanks
TheChief

2

It also depends on the wires and the other device (is it to the computer ?) and the USB bus.
Inside a computer the USB port could be shared with other USB ports. This will reduce the maximum speed a lot.

Is the microcontroller a ATmega328P ? If that chip is too slow, the bytes still get transmitted but the gaps between the burst of data is getting larger and larger.

Is the data only being transmitted ? Or is a protocol used that waits for data to be able to transmit the next buch of data ?

Read also other posts about the maximum baudrate:
http://arduino.cc/forum/index.php/topic,98364.0.html

3 
Just a simple sketch:

[code]
void setup() {
  Serial.begin(230400);
}


void loop() {
  if (Serial.available() > 0)
  {
      byte val = Serial.read();
      Serial.write(val); 
  }
}

Results are ok, sending 8 bytes.

Received (after 0ms): 9C DA 00 03 63 60 3B 36 
20ms waiting
Sending frame with 3 bytes
Received (after 0ms): 9C DA 00 03 49 0D 44 36 
20ms waiting
Sending frame with 3 bytes
Received (after 0ms): 9C DA 00 03 5A 5F 1A 36 
20ms waiting

Same procedure with 500k baud rate

Received (after 0ms): 9C DA 80 83 C9 8D C4 B6 
20ms waiting
Sending frame with 3 bytes
Received (after 0ms): 9C DA 80 83 DA DF 9A B6 
20ms waiting

First 4 bytes and last byte should always be the same, but with 500k i get different results.

The chipp supports the following baud rates:

75, 150, 300, 600, 1200, 1800, 2400, 3600,4800, 7200, 9600, 14400, 19200, 28800, 38400, 57600, 115200, 230400, 460800, 614400, 921600, 1228800, 2457600, 3000000 and 6000000, but this does not match 500k and 1M used in Arduino.[/code]

4

No more ideas to drivethe chip with more than 230400 baud?

5

At a certain moment you can only use whole dividers of the clock speed as only then you can get the timing right over the 10 bits of a byte.

Note that if there is a inaccuracy of 10% you will fail at least one bit (draw a timing/sample diagram) and at higher speeds every cpu ccyle becomes a larger percentage..

6

BTW, Arduino supports far more baud rates when tweaked a little. See - http://arduino.cc/forum/index.php?topic=138497.0 -

I got the Arduino also working on 345600, 400.000 and 500.000 but only for small (<10 ) char bursts, mainly sending.

Teensy2.0 however has the fastest Serial IO I used so far (claims 12 Mbit IIRC)