tools: Add PTY device detection for QEMU serial support.

Improve mpremote and pyboard.py serial connection handling to detect and
properly configure PTY devices. This enables running tests via QEMU's
serial PTY output.

Changes to transport_serial.py and pyboard.py to check if the serial
device is a PTY and adjust timeout/configuration accordingly.

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

Author: pi-anl

tools/mpremote/mpremote/transport_serial.py

@@ -35,7 +35,7 @@
 # Once the API is stabilised, the idea is that mpremote can be used both
 # as a command line tool and a library for interacting with devices.
 
-import ast, io, os, re, struct, sys, time
+import ast, io, os, re, stat, struct, sys, time
 import serial
 import serial.tools.list_ports
 from errno import EPERM, ENOTTY
@@ -105,6 +105,31 @@ def __init__(self, device, baudrate=115200, wait=0, exclusive=True, timeout=None
         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.
+        self.is_pty = self._is_pty_device(device)
+
+    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):
         # ESP Windows quirk: Prevent target from resetting when Windows clears DTR before RTS
         try:
@@ -140,22 +165,27 @@ 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
 

tools/pyboard.py

@@ -70,6 +70,7 @@
 import ast
 import errno
 import os
+import stat
 import struct
 import sys
 import time
@@ -333,6 +334,41 @@ 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.
+        if device.startswith("execpty:"):
+            # execpty: explicitly uses PTY devices
+            self.is_pty = True
+        elif device.startswith("exec:") or (
+            device and device[0].isdigit() and device[-1].isdigit() and device.count(".") == 3
+        ):
+            # exec: (non-PTY) and telnet connections are not PTYs
+            self.is_pty = False
+        else:
+            # For direct serial device paths, auto-detect
+            self.is_pty = self._is_pty_device(device)
+
+    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 +394,27 @@ 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