# HG changeset patch
# User Daniel O'Connor <doconnor@gsoft.com.au>
# Date 1611038601 -37800
# Node ID bf411c7f5e7871cb37ce4964b659dd36714de849
# Parent  29bcef5592839c0ca603b53d3bb7dea31174262d
Perform a dummy write/read after initiateClear and check the event/error queue bit.

diff -r 29bcef559283 -r bf411c7f5e78 usb488.py
--- a/usb488.py	Tue Jan 19 16:06:29 2021 +1030
+++ b/usb488.py	Tue Jan 19 17:13:21 2021 +1030
@@ -116,6 +116,9 @@
 STATUS_SPLIT_NOT_IN_PROGRESS = 0x82
 STATUS_SPLIT_IN_PROGRESS = 0x83
 
+# SCPI error/event queue status register bit
+STATUS_EVE_QUEUE = 0x04
+
 class USB488Device(object):
     def __init__(self, vendor = None, product = None, serial = None, path = None):
         """Search for a USB488 class device, if specified vendor,
@@ -213,7 +216,21 @@
             raise BaseException("Can't find bulk-out endpoint")
 
         self.tag = 1
+
+        # Flush out any pending data
         self.initiateClear()
+        # Perform dummy write/read otherwise the next read times out
+        try:
+            self.ask('*STB?', timeout = 0.001)
+        except usb.USBError:
+            pass
+        # Clear status register
+        for i in range(10):
+            self.write('*CLS')
+            if int(self.ask('*STB?')) & STATUS_EVE_QUEUE == 0:
+                break
+        else:
+            raise BaseException('Unable to clear status register')
 
     def __str__(self):
         rtn = "Mfg: %s Prod: %s" % (self.vendname, self.prodname)
@@ -221,7 +238,7 @@
             rtn += " S/N: " + self.serial
 
         return rtn
-    
+
     def incrtag(self):
         self.tag = (self.tag + 1) % 255
         if self.tag == 0:
@@ -250,7 +267,7 @@
 
         # Bump the tag
         self.incrtag()
-            
+
         # Split it up into maxPacket sized chunks and send..
         while len(pkt) > 0:
             chunk = pkt[0:self.maxPacket]