tools/pyboard: Add automatic PTY device detection for QEMU.

Apply the same PTY detection fix to pyboard.py as mpremote (commit 5fb9bc1).

The official test suite uses pyboard.py (tests/run-tests.py line 369), not
mpremote. Both tools received the same breaking change in commit aaedd59
(May 2025), so both need the fix.

This eliminates intermittent hangs when running tests against QEMU targets.

Signed-off-by: Andrew Leech <[email protected]>

Author: pi-anl

tools/pyboard.py

@@ -70,6 +70,7 @@
 import ast
 import errno
 import os
+import stat
 import struct
 import sys
 import time
@@ -333,6 +334,39 @@ def __init__(
             if delayed:
                 print("")
 
+        # Detect if this is a PTY device (e.g., QEMU serial output)
+        # PTY devices don't reliably report inWaiting() status, so we need
+        # to use blocking reads instead of checking for data availability.
+        # Only check for actual serial devices, not exec/telnet connections.
+        if not (
+            device.startswith("exec:")
+            or device.startswith("execpty:")
+            or (device and device[0].isdigit() and device[-1].isdigit() and device.count(".") == 3)
+        ):
+            self.is_pty = self._is_pty_device(device)
+        else:
+            self.is_pty = False
+
+    def _is_pty_device(self, device):
+        """
+        Detect if device is a PTY (pseudo-terminal).
+
+        PTY devices are commonly used by emulators like QEMU. Unlike real serial
+        devices, PTY inWaiting() may not report data availability correctly,
+        requiring use of blocking reads instead.
+        """
+        try:
+            # Linux Unix98 PTY pattern: /dev/pts/N
+            if device.startswith("/dev/pts/"):
+                st = os.stat(device)
+                # Unix98 PTY slaves have major device number 136 on Linux
+                if stat.S_ISCHR(st.st_mode) and os.major(st.st_rdev) == 136:
+                    return True
+        except (OSError, AttributeError):
+            # If detection fails or os.major not available, assume not a PTY
+            pass
+        return False
+
     def close(self):
         self.serial.close()
 
@@ -358,22 +392,27 @@ def read_until(
         while True:
             if data.endswith(ending):
                 break
-            elif self.serial.inWaiting() > 0:
+
+            # PTY: always read (blocking with timeout), Serial: check inWaiting() first
+            if self.is_pty or self.serial.inWaiting() > 0:
                 new_data = self.serial.read(1)
-                if data_consumer:
-                    data_consumer(new_data)
-                    data = new_data
-                else:
-                    data = data + new_data
-                begin_char_s = time.monotonic()
-            else:
-                if timeout is not None and time.monotonic() >= begin_char_s + timeout:
-                    break
-                if (
-                    timeout_overall is not None
-                    and time.monotonic() >= begin_overall_s + timeout_overall
-                ):
-                    break
+                if new_data:
+                    if data_consumer:
+                        data_consumer(new_data)
+                        data = new_data
+                    else:
+                        data = data + new_data
+                    begin_char_s = time.monotonic()
+
+            # Check timeouts (applies to both PTY and real serial)
+            if timeout is not None and time.monotonic() >= begin_char_s + timeout:
+                break
+            if (
+                timeout_overall is not None
+                and time.monotonic() >= begin_overall_s + timeout_overall
+            ):
+                break
+            if not self.is_pty:
                 time.sleep(0.01)
         return data