Handle BrailliantB devices that do not report their number of cells (#17526)

Partially fixes #17518

Summary of the issue:
Some HumanWare devices do not report the number of cells in their HID capabilities report. This is the case for Brailliant BI 40X since firmware 2.4.

Description of user facing changes
The Brailliant BI 40X and similar display with firmware version 2.4 is working correctly again.

Description of development approach
This PR fixes the issue by using the HID output report size to calculate the number of cells. If the device reports a cell count, this is still being used.

Testing strategy:
Tested with a Brailliant BI 40X over Bluetooth.

Known issues with pull request:
Since firmware 2.4 this device is recognized by the Standard HID driver over Bluetooth. However, the keys do not work using that driver. This PR does not fix the Standard HID driver.

Author: bramd

source/brailleDisplayDrivers/brailliantB.py

@@ -190,11 +190,27 @@ def __init__(self, port="auto"):
 
 	def _initAttempt(self):
 		if self.isHid:
+			# Ensure to set self.numCells only at the end of this method to prevent display writes before the capabilities/numCells request
+			numCells = 0
+			# First try to get cell count from _writeSize
+			try:
+				# _writeSize includes 4 bytes of overhead, so subtract 4
+				numCells = self._dev._writeSize - 4
+			except AttributeError:
+				log.debugWarning("Could not get _writeSize from HID device")
+
+			# Adjust numCells based on reported number of cells
 			try:
 				data: bytes = self._dev.getFeature(HR_CAPS)
+				reportedNumCells = data[24]
+				if reportedNumCells > 0:
+					# Update numCells based on reported cell count from the device
+					numCells = reportedNumCells
+				else:
+					log.debugWarning("Could not get number of cells from HID device using HR_CAPS")
 			except WindowsError:
 				return  # Fail!
-			self.numCells = data[24]
+			self.numCells = numCells
 		else:
 			# This will cause the display to return the number of cells.
 			# The _serOnReceive callback will see this and set self.numCells.

user_docs/en/changes.md

@@ -4,6 +4,8 @@
 
 ### Bug Fixes
 
+* Humanware Brailliant BI 40X devices running firmware version 2.4 now work as expected. (#17518, @bramd)
+
 ## 2024.4.1
 
 This is a patch release to fix a bug when saving speech symbol dictionaries.