OS X long delays between writes and multiple callbacks fired.

[programmarchy]

I'm using serialport to connect to a bluetooth module on an AVR micro with the following code:

#include <avr/io.h>
#include <avr/wdt.h>
#include <stdlib.h>

volatile uint8_t bt_rx;

int main(void)
{
    // usart
    UBRR1L = 25; // 38.4k
    UCSR1A |= _BV(U2X1);
    UCSR1A |= _BV(TXC1);
    UCSR1B |= (_BV(RXEN1) | _BV(TXEN1));
    UCSR1C |= (_BV(UCSZ11) | _BV(UCSZ10)); // 8 bits, 1 stop bit

    while (1)
    {
        wdt_reset();
        loop_until_bit_is_clear(UCSR1A, RXC1);
        bt_rx = UDR1;
    }
}

All this does is consume bytes sent to it, pretty simple.

I also wrote a node program to dump a file through serialport:

if (process.argv.length !== 4) {
    console.log('Usage: node test COM FILE');
    return 0;
}

var SerialPort = require('serialport').SerialPort;
var fs = require('fs');

var comPort = process.argv[2];
var inputFilePath = process.argv[3];

var serialPort = new SerialPort(comPort);
var inputData = fs.readFileSync(inputFilePath);

serialPort.on('open', function (err) {
    if (err) {
        console.error('open', err);
    } else {
        console.log('open');
        serialPort.write(inputData, function (err) {
            if (err) {
                console.error('write', err);
            } else {
                console.log('done')
            }
        });
    }
});

process.on('SIGINT', function() {
  serialPort.close();
});

Then I dump a binary file with 20000 bytes: node serialport COM4 input.bin

On Windows, everything goes great. The output goes:

open
done

And I have a logic analyzer connected to the USART on my Bluetooth module:

Everything comes in nice and smoothly.

On Mac, it's a totally different story. The output goes:

open
done
done
done
done
done
done
done
done
done
done
done
done
done
done
done
done
done
done
done

And the logic analyzer has huge gaps between data:

Has anyone seen this before? Anyone know if this an issue with SerialPort, or OS X?

I am running OS X Yosemite (which has been rife with Bluetooth issues since I upgraded from Mavericks).

[programmarchy]

This looks like it could be a hardware issue. Tested on a Mid 2010 MBP with Yosemite, and everything was great. Late 2012 MBP has issues.

[jacobrosenthal]

@programmarchy Any further updates? Was it that machine?

[programmarchy]

Yes, it was the machine. Thanks for ping back.

Still haven't figured out the problem with the machine, but the same exact code worked on another Mac of the same model.

Closing.