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# This is a simple serial port terminal demo.
#
# Its primary purpose is to demonstrate the native serial port access offered via
# win32file.
# It uses 3 threads:
# - The main thread, which cranks up the other 2 threads, then simply waits for them to exit.
# - The user-input thread - blocks waiting for a keyboard character, and when found sends it
# out the COM port. If the character is Ctrl+C, it stops, signalling the COM port thread to stop.
# - The COM port thread is simply listening for input on the COM port, and prints it to the screen.
# This demo uses userlapped IO, so that none of the read or write operations actually block (however,
# in this sample, the very next thing we do _is_ block - so it shows off the concepts even though it
# doesnt exploit them.
import msvcrt # For the getch() function.
import sys
import threading
import win32con # constants.
from win32event import * # We use events and the WaitFor[Multiple]Objects functions.
from win32file import * # The base COM port and file IO functions.
def FindModem():
# Snoop over the comports, seeing if it is likely we have a modem.
for i in range(1, 5):
port = "COM%d" % (i,)
try:
handle = CreateFile(
port,
win32con.GENERIC_READ | win32con.GENERIC_WRITE,
0, # exclusive access
None, # no security
win32con.OPEN_EXISTING,
win32con.FILE_ATTRIBUTE_NORMAL,
None,
)
# It appears that an available COM port will always success here,
# just return 0 for the status flags. We only care that it has _any_ status
# flags (and therefore probably a real modem)
if GetCommModemStatus(handle) != 0:
return port
except error:
pass # No port, or modem status failed.
return None
# A basic synchronous COM port file-like object
class SerialTTY:
def __init__(self, port):
if type(port) == type(0):
port = "COM%d" % (port,)
self.handle = CreateFile(
port,
win32con.GENERIC_READ | win32con.GENERIC_WRITE,
0, # exclusive access
None, # no security
win32con.OPEN_EXISTING,
win32con.FILE_ATTRIBUTE_NORMAL | win32con.FILE_FLAG_OVERLAPPED,
None,
)
# Tell the port we want a notification on each char.
SetCommMask(self.handle, EV_RXCHAR)
# Setup a 4k buffer
SetupComm(self.handle, 4096, 4096)
# Remove anything that was there
PurgeComm(
self.handle, PURGE_TXABORT | PURGE_RXABORT | PURGE_TXCLEAR | PURGE_RXCLEAR
)
# Setup for overlapped IO.
timeouts = 0xFFFFFFFF, 0, 1000, 0, 1000
SetCommTimeouts(self.handle, timeouts)
# Setup the connection info.
dcb = GetCommState(self.handle)
dcb.BaudRate = CBR_115200
dcb.ByteSize = 8
dcb.Parity = NOPARITY
dcb.StopBits = ONESTOPBIT
SetCommState(self.handle, dcb)
print("Connected to %s at %s baud" % (port, dcb.BaudRate))
def _UserInputReaderThread(self):
overlapped = OVERLAPPED()
overlapped.hEvent = CreateEvent(None, 1, 0, None)
try:
while 1:
ch = msvcrt.getch()
if ord(ch) == 3:
break
WriteFile(self.handle, ch, overlapped)
# Wait for the write to complete.
WaitForSingleObject(overlapped.hEvent, INFINITE)
finally:
SetEvent(self.eventStop)
def _ComPortThread(self):
overlapped = OVERLAPPED()
overlapped.hEvent = CreateEvent(None, 1, 0, None)
while 1:
# XXX - note we could _probably_ just use overlapped IO on the win32file.ReadFile() statement
# XXX but this tests the COM stuff!
rc, mask = WaitCommEvent(self.handle, overlapped)
if rc == 0: # Character already ready!
SetEvent(overlapped.hEvent)
rc = WaitForMultipleObjects(
[overlapped.hEvent, self.eventStop], 0, INFINITE
)
if rc == WAIT_OBJECT_0:
# Some input - read and print it
flags, comstat = ClearCommError(self.handle)
rc, data = ReadFile(self.handle, comstat.cbInQue, overlapped)
WaitForSingleObject(overlapped.hEvent, INFINITE)
sys.stdout.write(data)
else:
# Stop the thread!
# Just incase the user input thread uis still going, close it
sys.stdout.close()
break
def Run(self):
self.eventStop = CreateEvent(None, 0, 0, None)
# Start the reader and writer threads.
user_thread = threading.Thread(target=self._UserInputReaderThread)
user_thread.start()
com_thread = threading.Thread(target=self._ComPortThread)
com_thread.start()
user_thread.join()
com_thread.join()
if __name__ == "__main__":
print("Serial port terminal demo - press Ctrl+C to exit")
if len(sys.argv) <= 1:
port = FindModem()
if port is None:
print("No COM port specified, and no modem could be found")
print("Please re-run this script with the name of a COM port (eg COM3)")
sys.exit(1)
else:
port = sys.argv[1]
tty = SerialTTY(port)
tty.Run()