From 02230362e98c08338b79a3375a2fe9276ee69e39 Mon Sep 17 00:00:00 2001
From: Vincent Slotman <vincent.slotman@bench.com>
Date: Fri, 24 Mar 2017 18:37:04 +0100
Subject: [PATCH] Raise timeout exception if <4 bytes received

---
 usbtmc/usbtmc.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/usbtmc/usbtmc.py b/usbtmc/usbtmc.py
index 5e38af0..1773d29 100644
--- a/usbtmc/usbtmc.py
+++ b/usbtmc/usbtmc.py
@@ -655,6 +655,9 @@ def read_raw(self, num=-1):
 
                 resp = self.bulk_in_ep.read(read_len+USBTMC_HEADER_SIZE+3, timeout=self._timeout_ms)
 
+                if len(resp) < 4:
+                    raise usb.core.USBError('Operation timed out', errno=110)
+
                 if sys.version_info >= (3, 2):
                     resp = resp.tobytes()
                 else: