The received data is not complete

[Andy Smith]

When programming with uart.readline(), there is a problem that the received data is not complete.
How do I solve the problem?

[jcaron]

@Andy-Smith have you set timeout_chats in the UART constructor?

[neil jepsen]

Hi Andy,
coincidently I have been playing with reading a GPS and trying to get to the bottom of how the various uart instructions work, which is not entirely clear to me from the docs.
I have the following code running on a fipy'

import time
import utime
import socket
import machine
dir(machine)
import gc
from time import sleep
from machine import UART
from utime import sleep_ms, ticks_ms, ticks_diff,ticks_add
from machine import Pin
from machine import RTC
import pycom
import math


pycom.wifi_on_boot(False)
pycom.smart_config_on_boot(False)


valid = ""
latitude  = 0
longitude = 0
GMT_time= 0
satellites_used=0

gps=UART(1,baudrate=9600,pins =('P8','P13'),rx_buffer_size = 4096)
print('uart done')



def read_gps():
    
  try:
    t = utime.ticks_us()
    global gps,latitude,longitude,GMT_time,satellites_used
    if gps.any():
        print(gps.any())
        index = 0
        sleep(0.1)
        print('chars after 0.1 =',gps.any())
        nmea_str= str(gps.readline())   # reads from buffer not gps. looks like b'$  nema string  ' and is a byte array 
              
        print('gps said',nmea_str,'len=',len(nmea_str))
       
        if nmea_str.find('$GNGGA') >-1:     
                     
             index = nmea_str.strip().split(',')           # strip spaces, split on ','  split takes 17ms 
             valid = index[6]
             gps_time = index[1]                          #time is battery backed up
                                 
             
             if valid =='1':  
                    
                   latitude = index[2]
                   longitude=index[4]
                   GMT_time = index[1]
                   satellites_used = index[7]
#                    
             else:
                 print('invalid response',nmea_str,'validity = ',valid)
#                              
                
#            
        if nmea_str.find('$GPGSV') >-1:
                  index = nmea_str.strip().split(',')
                  print()
                  print()
                  print ('last good lat',latitude,'at time',GMT_time, 'from',satellites_used,'satellites')
                  print ('last good long',longitude)
                  print('satellites in view=',index[3], 'at time',GMT_time)
                  print()
                  print()
                  sleep(5)
                  print('chars=',gps.any())
                  gps.read()  #read all - flush buffer
                  print('chars after flush =',gps.any())
                 
  except Exception as e:   
            print("## failed to read GPS",e)
            

 
while True:
   r = read_gps()
  

The code runs OK. Things i have learned are:
uart.any() returns the number of bytes in the uart buffer.
If the buffer is too small and overflows, data is lost but the processor doesn't crash and
as far as I know other code/var/ are not overwritten
uart.readline() reads a line of code if there is a complete line in the buffer at that point in time.
Data is not removed from the buffer with uart.readline(), unlike uart.read()
uart.read() will read verything in the uart buffer and clear the buffer.
In the above code, whilst the first line of gps nmea data is being read and processed, GPS data is still coming in and being stored in the buffer.

[Andy Smith]

@neil-jepsen Thanks for your reply, I would like to know how this uart.readline() determines the end of reception.

[Andy Smith]

@jcaron Actually it doesn't, the data I receive in this one would be longer, something like ST<{"cmd_code": "set_value", "type": "label", "widget": "label2", "value":1.23, "format":"%.2f"}>ET.

[neil jepsen]

@Andy-Smith that line reads a GPS response which are coming in at 10 lines or more each second (depending on the gps) and the function falls out the end, only printing the ones that I am interested in decoding.