fixed timeout issue for big sdo block transfers

source/device.js

@@ -132,13 +132,14 @@ class Device extends EventEmitter {
      * @param {number} message.id - CAN message identifier.
      * @param {Buffer} message.data - CAN message data;
      * @param {number} message.len - CAN message length in bytes.
+     * @returns {number} number of bytes sent or -1 for error
      * @protected
      */
     send(message) {
         if(this._send === null)
             throw ReferenceError("please call setTransmitFunction() first");
 
-        this._send(message);
+        return this._send(message);
     }
 
     /**

source/protocol/sdo.js

@@ -311,9 +311,10 @@ class SdoTransfer {
      * Send a data buffer.
      *
      * @param {Buffer} data - data to send.
+     * @returns {number} Number of bits sent or -1 for error
      */
     send(data) {
-        this.device.send({
+        return this.device.send({
             id: this.cobId,
             data: data,
         });

source/protocol/sdo_client.js

@@ -96,6 +96,8 @@ class SdoClient {
         this.servers = {};
         this.transfers = {};
         this._blockSize = 127;
+        // Minimum timeout for the sdo block download.
+        this._blockDownloadTimeout = 1;
     }
 
     /**
@@ -641,6 +643,10 @@ class SdoClient {
                 return;
             }
 
+            if(this._blockDownloadTimeout > 1){
+                this._blockDownloadTimeout = this._blockDownloadTimeout >> 1;
+            }
+
             const sendBuffer = Buffer.alloc(8);
             const offset = 7 * (transfer.blockSequence
                 + (transfer.blockCount * transfer.blockSize));
@@ -652,15 +658,19 @@ class SdoClient {
             }
 
             transfer.data.copy(sendBuffer, 1, offset, offset + 7);
-            transfer.send(sendBuffer);
+            const ret = transfer.send(sendBuffer);
+            if(ret < 0 ){
+                this._blockDownloadTimeout = this._blockDownloadTimeout << 8;
+                transfer.blockSequence -= 1
+            }
             transfer.refresh();
 
             if(transfer.blockFinished
                 || transfer.blockSequence >= transfer.blockSize) {
                 clearInterval(transfer.blockInterval);
                 transfer.blockInterval = null;
             }
-        });
+        }, this._blockDownloadTimeout);
     }
 
     /**