General • Raspberry Pi Pico serial behaviour with CTS/RTS

Code:

#############  Sending side (Rpi3)Host_ser  Serial port open baud= 230400 and timeout = 0.05 ***** Starting RPI Serial TestHarness2 / (RPI-T3)        mainThrottle = 0.001 (RPI-T3) sending      Host_ser sending len=303 mess3 = b'\x1eUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU\x1e\n' (RPI-T3) sending UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUHost_ser sending len=8 mess3 = b'\x1e     \x1e\n' (RPI-T3) sending      Host_ser sending len=303 mess3 = b'\x1eUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU\x1e\n' (RPI-T3) sending UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUHost_ser sending len=8 mess3 = b'\x1e     \x1e\n' (repeats)

Code:

PICO_ser  Serial port open baud= 230400 and timeout = 0***** Starting Pico Serial TestHarness2 / (Pico-T3)        mainThrottle = 0.1PICO_ser messageBytes is len = 274PICO_ser messageBytes = b'\x1eUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU'PICO_ser  rc=1 >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>PICO_ser  messageBytes is len = 274PICO_ser  messagesBytes   = b'\x1eUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU'(Pico-T3)  rc=1 = Full message did not arrive (corruption or timeout or buffer overflow?)(Pico-T3)  rc=1 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<PICO_ser messageBytes is len = 303PICO_ser messageBytes = b'\x1eUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU\x1e\n'PICO_ser  returning messageList = ['UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU'](Pico-T3) have 1 response(s)= ['UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU']PICO_ser messageBytes is len = 278PICO_ser messageBytes = b'\x1eUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU'PICO_ser  rc=1 >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>PICO_ser  messageBytes is len = 278PICO_ser  messagesBytes   = b'\x1eUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU'(Pico-T3)  rc=1 = Full message did not arrive (corruption or timeout or buffer overflow?)(Pico-T3)  rc=1 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

Code:

# serial-2-serial has 2 parts 'TestHarness' and (dumb) Serial_in_out# and Serial_in_out has several flavours, Pico, RPi, Jetson...from machine import UART, Pin # we need to import UART to use itimport timeclass SerialInOut:    ########## Class Attributes (shared by all instances of the class)    #  Record seperator (RS) = 0x1E  = 30 decimal    RS  = '\x1E'    #  chr(30) Type = <class 'str'>    RSb = b'\x1E'   #          Type = <class 'bytes'>    NL  = '\x0A'    # one end calls this NL and one LF but that is the same char(10) == \x0A    NLb = b'\x0A'     # MAXMsgLen = 4000    G_MyName = "Pico SerialInOut"    G_MyTag  = "PICO_ser "    ## Constructor(s) *********************************************************************    # WARNING for normal Python (RPI) timeout is 'maximum time to wait for the requested number of bytes to be received'    #         for microPython (Pico)  timeout is 'time (in milliseconds) to wait for the FIRST CHARACTER to arrive'    def __init__(self,     UartNo=0, TXPinNo=16, RXPinNo=17, baudrate=57600, timeout=0, CTSPinNo=18, RTSPinNo=19, port="tester"):        ########## instance Attributes        self.serNum     = UartNo        self.port       = port  #NA for Pico        self.baudrate   = baudrate        #self.timeoutSec = timeout       # Rpi3 wants sec        self.timeoutMs  = timeout       # Pico wants ms        self.txPin      = Pin(TXPinNo)        self.rxPin      = Pin(RXPinNo)        self.CTSPin     = Pin(CTSPinNo)        self.RTSPin     = Pin(RTSPinNo)                ########## Constructor actions        # Step 1. initialize the UART        try:            self.ser = UART(self.serNum,                baudrate = self.baudrate ,                 tx       = self.txPin,                 rx       = self.rxPin,                 timeout  = self.timeoutMs,                 cts      = self.CTSPin,                rts      = self.RTSPin                )            self.ser.init(rxbuf = 512,      # default was 256                # timeout_char = 1000,    no effect                flow     = UART.RTS | UART.CTS                )            print(f"{self.G_MyTag} Serial port open baud= {self.baudrate} and timeout = {self.timeoutMs} ")            print(f"{self.ser}")        except:            print(f"{self.G_MyTag} Error opening Serial / UART on pins {self.txPin}: {self.txPin}")            raise        # Give the serial port time to initialize        time.sleep(0.5)    ########## Class Methods    def send(self, message):        mess2 = self.RS + message + self.RS + self.NL        mess3 = mess2.encode('utf-8')                       # split out so we can print it 1st        print (f"{self.G_MyTag}sending mess3 = {mess3} ")            self.ser.write(mess3) # Encode the string to bytes        # self.ser.write(mess2.encode('utf-8')) # Encode the string to bytes and send in one step    # READ     # returns a 'rc' also    #   0 = OK    #   1 = Full message did not arrive (corruption or timeout or buffer overflow?)     #   2 = Fail - 1st byte is not a RS    #   3 = Fail - last byte is not a RS    #  and returns the message list or an empty list if there is nothing waiting or there is an error    def receive(self):        rc = 0        # if self.ser.in_waiting > 0:     # Rpi        if self.ser.any():                # Pico            #messageBytes = self.ser.read_until()          #  RPI    was (self.MAXMsgLen)            messageBytes = self.ser.readline()          #  Pico     was (self.MAXMsgLen)            # print (f"{self.G_MyTag} messageBytes is of type {type(messageBytes)} ")  # <class 'bytes'>            print (f"{self.G_MyTag} messageBytes is len = {len(messageBytes)} ")     # 1993 Next one was 4486!            print (f"{self.G_MyTag} messageBytes = {messageBytes} ")                        # stop compiler errors/warnings            if messageBytes is None:                return rc, []            # validation            # did the full message arrive including the NL?            if messageBytes[-1] != self.NLb[0]:     # RSb[0]:                rc = 1  #print(" Full message did not arrive (corruption or timeout or buffer overflow?) ")             elif messageBytes[0] != self.RSb[0]:                rc = 2  #print(" Fail: 1st byte is not a RS")    # This is important - we can receive just the tail of a message            elif messageBytes[-2] != self.RSb[0]:                rc = 3  #print(" Fail: last byte is not a RS")             if rc != 0:                print (f"{self.G_MyTag} rc={rc} >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>")                 print (f"{self.G_MyTag} messageBytes is len = {len(messageBytes)} ")     # 1993 Next one was 4486!                #print (f"{self.G_MyTag} messagesBytes!r = {messageBytes!r} ")  # !r : Applies repr() to the value, providing a developer-focused representation useful for debugging.                print (f"{self.G_MyTag} messagesBytes   = {messageBytes} ")                  self.ser.read()                    # Pico try and purge the buffer                 # self.ser.reset_input_buffer()    # RPI  try and purge the buffer                 return rc, []            messages = messageBytes[:-1].decode('utf-8') # , in pico there is no option > "errors='ignore' " # this .decode() removes the byte string format; strip() removes all common leading and trailing whitespace             # print (f"     messages = {messages} ")            tempList    = messages.split(self.RS)  # this will create empty items - especially at <end> <start> sequences            messageList = list(filter(None, tempList))  #delete all empty items            print(f"{self.G_MyTag} returning messageList = {messageList}")            return rc, messageList        else:            return rc, []

Code:

# 2026/02/04 V3 enabling hardware flow control (CTS/RTS)#               (just pass the pin numbers in)#from serial_in_out_RPi import SerialInOutfrom serial_in_out_pico import SerialInOutfrom machine import Timerimport time# ================================================================# ===  Call-back Functions for Threads# ================================================================    ##############################################################################    # handle_burst_mode_trigger    #   just the variable to trigger the output    ##############################################################################def handle_burst_mode_trigger(t):      # Pico has parm 't'#def handle_burst_mode_trigger():      # Rpi has no Parm    global G_doSendBurst    G_doSendBurst     = True # ================================================================# ===  Initialize# ================================================================G_MyName = "Pico Serial TestHarness3"G_MyTag  = "(Pico-T3) "# instantiate a SerialInOut object# for baudrate choose from 115200, 230400, 460800 (obviously both end have to be the same)test_uart = SerialInOut(UartNo=0, TXPinNo=16, RXPinNo=17, baudrate=230400, CTSPinNo=18, RTSPinNo=19)  # for Pico need to specify which Uart and pins# test_uart = SerialInOut(baudrate=230400, port='/dev/serial0')  # for RPi-3 "/dev/ttyUSB0 is the USB-2-serial breakout, /dev/serial0 is via pins 14/15"port='/dev/serial0'# test_uart = SerialInOut(baudrate=230400, port='/dev/ttyUSB0' ) # for PCmsg2Send = ['First',    #300 char        "300UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU"             ]            # pause time - make it different for each end to prove, almost, that multiple messages will queue up#pauseTime = 5 #in secondsbatch_sent   = FalsemainThrottle = 0.01 #in seconds (at 0.01 the 'swamp' of messages was handled. At 0.1 and even 0.02 they were truncated)######## items concerned with sending the output messages in a 'burst'G_doSendBurst      = FalseG_timer_send_every =  10000      # millisec. How ofter we send our batch of messages out# PicoburstTimer      = Timer(-1)## disable following 'burstTimer.init()' line to suppress outgoing messagesburstTimer.init(mode=Timer.PERIODIC, period=G_timer_send_every, callback=handle_burst_mode_trigger)# RPI#   burstTimer         = threading.Timer(G_timer_send_every, handle_burst_mode_trigger)      # RPI / normal python#   burstTimer.daemon  = True#   # disable following 'burstTimer.start' line to suppress outgoing messages#   burstTimer.start()      # RPI / normal pythonNoResponsesReceivedCount = 0# receive return-code decodes RC_decode = {        0: "OK",        #  - and Message is in 2nd return var    1: "Full message did not arrive (corruption or timeout or buffer overflow?) ",    2: "Fail - 1st byte is not a RS ",    3: "Fail - last byte is not a RS ",    4: "Fail - ",    5: "Fail - ",    6: "Fail - ",}print(f"***** Starting {G_MyName} / {G_MyTag}       mainThrottle = {mainThrottle} ")# ================================================================# ===               Main Code Loop                             ===# ================================================================try:    while True:        if G_doSendBurst:            for m in msg2Send:                test_uart.send(m)  # Send message to the other device (Pico or RPi or Jetson)                print(f"{G_MyTag}sending {m}")            G_doSendBurst = False        # now just listen a lot - quickly        rc, respList = test_uart.receive()        if rc != 0:            print(f"{G_MyTag} rc={rc} = {RC_decode.get(rc)}")            print (f"{G_MyTag} rc={rc} <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<")         # The childSerial will return an empty list if there is an error         if respList:   # list is NOT empty            print(f"{G_MyTag}have {len(respList)} response(s)= {respList}")            print(f"{G_MyTag} interveening 'No responses' received = {NoResponsesReceivedCount} ")            NoResponsesReceivedCount = 0        else:            NoResponsesReceivedCount += 1        time.sleep(mainThrottle)      # Wait for 'n' secondsexcept KeyboardInterrupt:     print("Program stopped by user")