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/*
* This file is part of Espruino, a JavaScript interpreter for Microcontrollers
*
* Copyright (C) 2013 Gordon Williams <gw@pur3.co.uk>
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*/
var AudioContext = window.AudioContext || window.webkitAudioContext;
var context = new AudioContext();
// some devices output an inverted waveform, some don't
var audio_serial_invert = false;
/** Send the given string of data out over audio.
This adds a 1 second preamble/postable to give the
capacitor time to charge (so we get a full 2V swing
on the output.
If you send characters outside the range 0-255,
they will be interpreted as a break (so not transmitted).
*/
function audio_serial_write(data, callback) {
var sampleRate = 44100;
var header = sampleRate; // 1 sec to charge/discharge the cap
var baud = 9600;
var samplesPerByte = parseInt(sampleRate*11/baud);
var bufferSize = samplesPerByte*data.length/*samples*/ + header*2;
var buffer = context.createBuffer(1, bufferSize, sampleRate);
var b = buffer.getChannelData(0);
for (var i=0;i<header;i++) b[i]=i / header;
var offset = header;
data.split("").forEach(function(c) {
var byte = c.charCodeAt(0);
if (byte>=0 && byte<=255) {
for (var i=0;i<samplesPerByte;i++) {
var bit = Math.round(i*baud/sampleRate);
var value = 1;
if (bit==0) value=0; // start bit
else if (bit==9 || bit==10) value=1; // stop bits
else value = (byte&(1<<(bit-1))) ? 1 : 0; // data
b[offset++] = value*2-1;
}
} else {
// just insert a pause
for (var i=0;i<samplesPerByte;i++)
b[offset++] = 1;
}
});
for (var i=0;i<header;i++) b[offset+i]=1-(i / header);
if (audio_serial_invert)
for (var i=0;i<bufferSize;i++) b[i] = 1-b[i];
var source = context.createBufferSource();
source.buffer = buffer;
source.connect(context.destination);
source.start();
if (callback)
window.setTimeout(callback, 1000*bufferSize/sampleRate);
}