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

Applies the same PTY detection fix to pyboard.py as mpremote.
The official test suite uses pyboard.py (tests/run-tests.py),
so both tools need the fix.

See PR micropython#18327 for detailed analysis and validation.

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