From caea7bb39d174095531cb86080c3552735139137 Mon Sep 17 00:00:00 2001
From: Alex McLean <alex@slab.org>
Date: Fri, 2 Dec 2022 10:45:01 +0000
Subject: [PATCH] Support sending CRC16 bytes with serial messages (#276)

Optionally add a crc16 checksum.
Optionally support sending names in name/value pairs as single characters
---
 packages/serial/serial.mjs | 78 +++++++++++++++++++++++++++++---------
 1 file changed, 60 insertions(+), 18 deletions(-)

diff --git a/packages/serial/serial.mjs b/packages/serial/serial.mjs
index 27f2bb58..e5e7c188 100644
--- a/packages/serial/serial.mjs
+++ b/packages/serial/serial.mjs
@@ -6,7 +6,7 @@ This program is free software: you can redistribute it and/or modify it under th
 
 import { Pattern, isPattern } from '@strudel.cycles/core';
 
-var serialWriter;
+var writeMessage;
 var choosing = false;
 
 export async function getWriter(br = 38400) {
@@ -14,18 +14,30 @@ export async function getWriter(br = 38400) {
     return;
   }
   choosing = true;
-  if (serialWriter) {
-    return serialWriter;
+  if (writeMessage) {
+    return writeMessage;
   }
   if ('serial' in navigator) {
     const port = await navigator.serial.requestPort();
     await port.open({ baudRate: br });
-    // eslint-disable-next-line no-undef
-    const textEncoder = new TextEncoderStream();
-    const writableStreamClosed = textEncoder.readable.pipeTo(port.writable);
-    const writer = textEncoder.writable.getWriter();
-    serialWriter = function (message) {
-      writer.write(message);
+    const encoder = new TextEncoder();
+    const writer = port.writable.getWriter();
+    writeMessage = function (message, chk) {
+      const encoded = encoder.encode(message)
+      if (!chk) {
+        writer.write(encoded);
+      }
+      else {
+        const bytes = new Uint8Array(4);
+        bytes[0] = 124; // | symbol
+        bytes[1] = (chk >> 8) & 0xFF;
+        bytes[2] = chk & 0xFF;
+        bytes[3] = 59; // semicolon
+        const withchk = new Uint8Array(encoded.length+4)
+        withchk.set(encoded);
+        withchk.set(bytes, encoded.length);
+        writer.write(withchk);
+      }
     };
   } else {
     throw 'Webserial is not available in this browser.';
@@ -34,18 +46,41 @@ export async function getWriter(br = 38400) {
 
 const latency = 0.1;
 
-Pattern.prototype.serial = function (...args) {
-  return this._withHap((hap) => {
-    if (!serialWriter) {
-      getWriter(...args);
+// crc16 (CCITT-FALSE) https://gist.github.com/tijnkooijmans/10981093
+function crc16(data) {
+  const length = data.length
+  if (length == 0) {
+    return 0;
+  }
+
+  var crc = 0xFFFF;
+  for (var i = 0; i < length; ++i) {
+    crc ^= data.charCodeAt(i) << 8;
+    for (var j = 0; j < 8; ++j) {
+      crc = (crc & 0x8000) > 0 ? (crc << 1) ^ 0x1021 : crc << 1;
+    }
+  }
+
+  return crc & 0xffff;
+}
+
+Pattern.prototype.serial = function (br=38400,sendcrc=false,singlecharids=false) {
+  return this.withHap((hap) => {
+    if (!writeMessage) {
+      getWriter(br);
     }
     const onTrigger = (time, hap, currentTime) => {
       var message = '';
+      var chk = 0;
       if (typeof hap.value === 'object') {
         if ('action' in hap.value) {
-          message += hap.value['action'] + '(';
+          var action = hap.value['action'];
+          if (singlecharids) {
+            action = action.charAt(0);
+          }
+          message += action + '(';
           var first = true;
-          for (const [key, val] of Object.entries(hap.value)) {
+          for (var [key, val] of Object.entries(hap.value)) {
             if (key === 'action') {
               continue;
             }
@@ -54,19 +89,26 @@ Pattern.prototype.serial = function (...args) {
             } else {
               message += ',';
             }
-            message += `${key}:${val}`;
+            if (singlecharids) {
+              key = key.charAt(0);
+            }
+            message += key + ':' + val;
           }
           message += ')';
+          if (sendcrc) {
+            chk = crc16(message)
+          }
         } else {
           for (const [key, val] of Object.entries(hap.value)) {
-            message += `${key}:${val};`;
+            message += `${key}:${val}`;
           }
         }
       } else {
         message = hap.value;
       }
       const offset = (time - currentTime + latency) * 1000;
-      window.setTimeout(serialWriter, offset, message);
+
+      window.setTimeout(function () {writeMessage(message, chk)}, offset);
     };
     return hap.setContext({ ...hap.context, onTrigger, dominantTrigger: true });
   });