From 9ad1fd8f25328c35a92e67ceac95c93d6d3dddab Mon Sep 17 00:00:00 2001
From: Robert Jordens <rj@m-labs.hk>
Date: Tue, 20 Mar 2018 17:40:03 +0100
Subject: [PATCH] urukul: add comment and doc about the AD9910 MASTER_RESET

---
 artiq/coredevice/urukul.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/artiq/coredevice/urukul.py b/artiq/coredevice/urukul.py
index c9c3edf4e..d2739a6d3 100644
--- a/artiq/coredevice/urukul.py
+++ b/artiq/coredevice/urukul.py
@@ -166,9 +166,12 @@ class CPLD:
     def init(self):
         """Initialize and detect Urukul.
 
-        Resets the DDS and verifies correct CPLD gateware version.
+        Resets the DDS I/O interface and verifies correct CPLD gateware
+        version.
+        Does not pulse the DDS MASTER_RESET as that confuses the AD9910.
         """
         cfg = self.cfg_reg
+        # Don't pulse MASTER_RESET (m-labs/artiq#940)
         self.cfg_reg = cfg | (0 << CFG_RST) | (1 << CFG_IO_RST)
         proto_rev = urukul_sta_proto_rev(self.sta_read())
         if proto_rev != STA_PROTO_REV_MATCH: