pySerial : Can't read data more than 8 characters

Question

I use pyserial to write and read between two Raspberry pi(s) via UART

Raspberry pi 1 : send data to Raspberry pi 2

    while 1:
        ser=serial.Serial('/dev/ttyAMA0')
        if not ser.isOpen():
            ser.open()
        msg=raw_input('RPi 1 send:')
        ser.write(msg)
        ser.close()

Raspberry pi 2 : receive data from Raspberry pi 1

    while 1:
        ser=serial.Serial('/dev/ttyAMA0' ,timeout=0)
        if not ser.isOpen():
            ser.open()
        data=ser.read(1024)
        if data.__len__()>0:
            print 'RPi 2 receive:',data
        ser.close()

I run both code.

and send data

    RPi 1 send : Hello

and receive data

    RPi 2 receive : Hello

But if RPi 1 send data more than 8 characters

for example

    RPi 1 send : Hello Raspberry pi NO.2

The result is

    RPi 2 receive: Hello Ra
    RPi 2 receive: spberry 
    RPi 2 receive: pi NO.2

This is my problem. Because I want it to receive like this

(RPi 2 receive: Hello Raspberry pi NO.2) #show only one line.

and if send (more 8 char) again, it show in a new line.

What code to join it in one line? or other way to do this? :)

Answer 1

I like to do this

sender.py

delim = "\x00"
ser.write(msg+delim)

reciever.py

delim = "\x00"
recvd = "".join(iter(lambda:ser.read(1),delim))
print recvd

Answer 2

When reading using ser.read, you're just reading what is already in the buffer, or waiting for chars to arrive in the buffer. The size you specify is a maximum number of chars to receive, but it can be much less as you experienced.

You have 2 easy solutions:

1. use ser.readline and put a terminator in your strings (like \n)
2. if you know in advance how many characters to read, repeat reading until you've received them all

In both cases, specify a timeout (for example 1 second) when opening the serial line, to get back control on your code if the remote end doesn't send anything for whatever reason.

Hope it helps.