add API to disable serial padding. (#2145)

* add API to desiable serial padding.

* renamed api

libs/core/serial.ts

@@ -8,6 +8,7 @@ namespace serial {
      * The string used to mark a new line, default is \r\n
      */
     export let NEW_LINE = "\r\n";
+    let writeLinePadding = 32;
 
     /**
      * Print a line of text to the serial port
@@ -19,15 +20,31 @@ namespace serial {
     //% text.shadowOptions.toString=true
     export function writeLine(text: string): void {
         if (!text) text = "";
+        serial.writeString(text);
         // pad data to the 32 byte boundary
         // to ensure apps receive the packet
-        let r = (32 - (text.length + 2) % 32) % 32;
+        if (writeLinePadding > 0) {
-        serial.writeString(text);
+            let r = (writeLinePadding - (text.length + NEW_LINE.length) % writeLinePadding) % writeLinePadding;
             for (let i = 0; i < r; ++i)
                 serial.writeString(" ");
+        }
         serial.writeString(NEW_LINE);
     }
 
+    /**
+     * Sets the padding length for lines sent with "write line".
+     * @param length the number of bytes alignment, eg: 0
+     *
+     */
+    //% weight=1
+    //% help=serial/set-write-line-padding
+    //% blockId=serialWriteNewLinePadding block="serial set write line padding to $length"
+    //% advanced=true
+    //% length.min=0 length.max=128
+    export function setWriteLinePadding(length: number) {
+        writeLinePadding = length | 0;
+    }
+
     /**
      * Print a numeric value to the serial port
      */