Faster Serial Communication?

Forum 2005-2010 (read only) Software Interfacing
1

I think I'm going to build an electronic drum kit with my Arduino. I just wrote a bit of code for a bass pedal:

int butpin = 2;
int last;
int but;


void setup() {
  Serial.begin(31250);
  pinMode(butpin, INPUT);
}

void loop() {
  but = digitalRead(butpin);
 if (but == HIGH && last == 0){
   noteOff(1, 20, 0);
   last = 1;
 } else{
 }
 if (but == LOW && last == 1){
   noteOn(1, 20, 64);
   last = 0;
 } else {
 }
// delay(1);
}

void noteOn(byte channel, byte note, byte velocity) {
  midiMsg( (0x90 | (channel & 0xf)), note, velocity);
}

// Send a MIDI note-off message.  Like releasing a piano key
void noteOff(byte channel, byte note, byte velocity) {
  midiMsg( (0x80 | (channel & 0xf)), note, velocity);
}


// Send a general MIDI message
void midiMsg(byte cmd, byte data1, byte data2) {
  //digitalWrite(ledPin,HIGH);  // indicate we're sending MIDI data
  Serial.print(cmd, BYTE);
  Serial.print(data1, BYTE);
  Serial.print(data2, BYTE);
  //digitalWrite(ledPin,LOW);
}

When I press the pedal it sends a midi note(yippy). The only issue is I can hear the lag. Right now I have my Arduino hooked up to a USB1.1 port, will I gain any speed by using a USB2.0 port? Is there any way for me to improve this performance? My expansion plans involve piezos and the analog pins. There isn't much point in continuing if I can't significantly reduce this lag.

Right now I'm running the Roland Serial Midi driver.

Thanks in advance.

2

You should be able to send somewhere between close to 3K characters a second with the serial (unless there is software overhead I am missing). However digitalRead has some error checking and has a significant delay. As I recall, it is around 1/60 of a second.

If digitalRead/Write are slowing you down you can read/write directly to the port close to 4million times a second. Look up "port manipulation". There are several forum posts on the subject. The serialWrite code is pretty tight and I doubt you could do it any faster than the library.

3

As I recall, it is around 1/60 of a second.

No it's not it's closer to 0.4mS. If you can hear any lag then it is the rest of the system not what you posted here.

USB1.1 port, will I gain any speed by using a USB2.0 port?

No you are just using serial bridge running at the MIDI rate.

Are you feeding the Arduino MIDI output directly into your system or is there some other software in between?

4

i have heard of lag in MIDI if you send more then one note and keep sending the overhead, you will heard the lag, but if you send 3 note in the same message that lag should not be there!
Not sure if this is what you need

5

Thanks for the info, it's quite helpful. After your posts I focused on my software rather than my code/the arduino. Turns out that Ableton Live is just really slow. Maybe it is my computer though. I changed programs and it responds MUCH faster.