From 94e7bb511b720f4ac795ad2016ffbf2b8d24856d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20C=C3=B4t=C3=A9?= <dccote@cervo.ulaval.ca>
Date: Mon, 18 May 2026 15:10:28 -0400
Subject: [PATCH] Match Sutter MP-285 GET_POSITION 13-byte reply (no prefix
 echo)

The library expected a 14-byte reply for GET_POSITION:
<xlllx> = pad + 3 int32 + terminator, where the leading pad is
the echoed command prefix 'C'. Testing against live hardware
(serial SIDCACD9, after a power cycle) showed the device replies
with only 13 bytes: 3 int32 + b'\r' -- no prefix echo.

The protocol has two reply modes (echo on / off). The mode appears
to depend on firmware state and is reset by a power cycle. The
prior 14-byte assumption worked for the previous device state
earlier in the session; this commit accepts the no-echo mode.

Changes:
- SutterDevice.commands['GET_POSITION']:
    replyDataLength: 14 -> 13
    unpackingMask:   '<xlllx' -> '<lllx'
    responseFormat:  '<clllc' -> '<lllc'      (mock side)
    responseFields:  drops 'header'           (mock side)
- DebugSerialPort.process_command for 'GET_POSITION':
    drops the {'header': b'c', ...} entry in the returned dict.
- testSutterSerialPort.py::testMoveGet:
    readData length: 14 -> 13
    unpack format: '<xlllx' -> '<lllx'

Caveat: if a future MP-285 boots into echo-on mode, this commit
will break GET_POSITION for it. The robust long-term fix is
either to detect/toggle the mode at init or to accept both reply
lengths. Filed as a follow-up to be addressed before this is
trusted across all MP-285 firmwares.

Verified against live hardware: 7/7 SutterDevice tests pass with
real stage motion (1.33s testDeviceMoveBy, 0.91s testDeviceMove,
0.89s testDeviceHome) and 7/7 DebugSerialPort tests still pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 hardwarelibrary/motion/sutterdevice.py        | 9 ++++-----
 hardwarelibrary/tests/testSutterSerialPort.py | 4 ++--
 2 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/hardwarelibrary/motion/sutterdevice.py b/hardwarelibrary/motion/sutterdevice.py
index 3e6500ad..c7abc73a 100644
--- a/hardwarelibrary/motion/sutterdevice.py
+++ b/hardwarelibrary/motion/sutterdevice.py
@@ -25,9 +25,9 @@ class SutterDevice(LinearMotionDevice):
                             replyDataLength=1, unpackingMask='<c'),
         "GET_POSITION": DataCommand(name="GET_POSITION", prefix=b'C',
                                     data=pack('<cc', b'C', b'\r'),
-                                    replyDataLength=14, unpackingMask='<xlllx',
-                                    responseFormat='<clllc',
-                                    responseFields=('header', 'x', 'y', 'z', 'terminator')),
+                                    replyDataLength=13, unpackingMask='<lllx',
+                                    responseFormat='<lllc',
+                                    responseFields=('x', 'y', 'z', 'terminator')),
         "HOME": DataCommand(name="HOME", prefix=b'H',
                             data=pack('<cc', b'H', b'\r'),
                             replyDataLength=1, unpackingMask='<c'),
@@ -172,8 +172,7 @@ def process_command(self, name, params, endPointIndex):
                 self.zSteps = params['z']
                 return b'\r'
             elif name == 'GET_POSITION':
-                return {'header': b'c', 'x': self.xSteps,
-                        'y': self.ySteps, 'z': self.zSteps,
+                return {'x': self.xSteps, 'y': self.ySteps, 'z': self.zSteps,
                         'terminator': b'\r'}
             elif name == 'HOME':
                 self.xSteps = self.ySteps = self.zSteps = 0
diff --git a/hardwarelibrary/tests/testSutterSerialPort.py b/hardwarelibrary/tests/testSutterSerialPort.py
index d506dc6f..85f7a553 100644
--- a/hardwarelibrary/tests/testSutterSerialPort.py
+++ b/hardwarelibrary/tests/testSutterSerialPort.py
@@ -56,8 +56,8 @@ def testMoveGet(self):
 
             payload = bytearray('c',encoding='utf-8')
             self.port.writeData(payload)
-            data = self.port.readData(length=1 + 4*3 + 1)
-            (x,y,z) = unpack("<xlllx", data)
+            data = self.port.readData(length=4*3 + 1)
+            (x,y,z) = unpack("<lllx", data)
             self.assertTrue( x == 1)
             self.assertTrue( y == 2)
             self.assertTrue( z == 3)