From f4452865d16cd60a5aee1fecd926e96b48b39bf1 Mon Sep 17 00:00:00 2001
From: Alex <akazaev@proton.me>
Date: Sun, 12 Apr 2026 17:30:29 -0500
Subject: [PATCH] Fix USB read length to match official tool protocol

The XVF3800 expects exact wLength: count * type_size + 1 (status byte).
Requesting wrong length caused stale/corrupted responses when polling.
Split _read into _read_uint16 and _read_float matching official format.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 xvf3800.py | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/xvf3800.py b/xvf3800.py
index 1d06eea..cd98e5e 100644
--- a/xvf3800.py
+++ b/xvf3800.py
@@ -53,17 +53,25 @@ class XVF3800:
         # don't call set_configuration() or detach_kernel_driver(),
         # the audio driver needs to keep its interface.
 
-    def _read(self, resid: int, cmdid: int, length: int) -> bytes:
-        """Read parameter via USB control transfer.
-        wValue = cmdid | 0x80 (read flag), wIndex = resid."""
+    def _read_uint16(self, resid: int, cmdid: int, count: int) -> bytes:
+        """Read uint16 parameters. Returns raw bytes including 1-byte status header."""
         try:
+            length = count * 2 + 1  # +1 for status byte
             data = self.dev.ctrl_transfer(
                 CTRL_REQUEST_TYPE_IN, 0,
-                0x80 | cmdid,  # wValue: cmdid with read bit
-                resid,         # wIndex: resource ID
-                length * 4,    # bytes to read (length is in words)
-                timeout=1000
-            )
+                0x80 | cmdid, resid, length, timeout=1000)
+            return bytes(data)
+        except Exception as e:
+            logger.debug("USB read error (resid=%d, cmd=%d): %s", resid, cmdid, e)
+            return b""
+
+    def _read_float(self, resid: int, cmdid: int, count: int) -> bytes:
+        """Read float32 parameters. Returns raw bytes including 1-byte status header."""
+        try:
+            length = count * 4 + 1  # +1 for status byte
+            data = self.dev.ctrl_transfer(
+                CTRL_REQUEST_TYPE_IN, 0,
+                0x80 | cmdid, resid, length, timeout=1000)
             return bytes(data)
         except Exception as e:
             logger.debug("USB read error (resid=%d, cmd=%d): %s", resid, cmdid, e)
@@ -88,10 +96,10 @@ class XVF3800:
     def read_doa(self) -> tuple[int, bool]:
         """Read Direction of Arrival. Returns (angle 0-359, vad True/False).
         Response format: 1 status byte + 2 uint16 words (angle, vad)."""
-        data = self._read(GPO_RESID, DOA_VALUE_CMD, 2)  # 2 uint16 words
-        if len(data) < 5:  # 1 header + 4 data bytes
+        data = self._read_uint16(GPO_RESID, DOA_VALUE_CMD, 2)
+        if len(data) < 5:
             return 0, False
-        angle, vad = struct.unpack_from("<HH", data, 1)  # skip 1-byte header
+        angle, vad = struct.unpack_from("<HH", data, 1)  # skip status byte
         return angle % 360, bool(vad)
 
     # --- LEDs ---