MKR1500 SARA R4 max baudrate and ftp REST command

Official Hardware MKR Family MKR NB 1500
1

I'm trying to find a 4G modem suitable to send data to a ftp. It thought it would be an easy task, but it's definitely not. Documentations are really basic and do not cope with real examples.
I have many issues with the SIM7600 modem using the FTP protocol. Then I wanted to try the MKR1500.

Until now, I get better results but I identified 2 big issues:

  1. The REST command (to resume transfer) is not properly implemented by SARA R4 (same issue with SIM7600), and FileZilla server does not handle it. Here is the log of fileZilla server:
[Command] REST 10
[Response] 350 Restarting at 10                 <==== RESUME at byte 10 =====>
[Command] PASV
[Trace] Trying listen(1, 64386) for data connection.
[Response] 227 Entering Passive Mode (X,X,148,107,251,130)
[Command] STOR example.txt
[Trace] open_file(C:\Users\...\Ftp\example.txt): fd = 880, res = 0

The last line shows the "res" value is not taken into account.
The file is erased and bytes are written at the beginning of the file.

  1. It is said on https://docs.arduino.cc/hardware/mkr-nb-1500 webpage, the datarate of LTE could reach UL 375 kbps / DL 300 kbps. But the maximum baudrate supported by the SARA-R410M-02B-00 is limited to 115200 so that webpage is wrong and misleading.
    I tried anyway to increase to 230400 since I was not sure of the two last digit of my modem version: Model: SARA-R410M-02B / Revision: L0.0.00.00.05.06 [Feb 03 2018 13:00:41]
    It seems impossible to go higher than 115200 (lower is ok) which results in a datarate of 1/3 of what I bought the module for. I managed to send 1MB of data at this datarate.
    Does anyone manage (after updating the firmware) to use higher baudrate (460800) ?

I attached a very simple ino sketch to test this with the MKR NB 1500.
mkr1500_2.ino (3,6 Ko)
To change the baudrate to 460800, send the char '#'. Send the char '%' to restore the value to 115200. The output of the file is:

Module MKR 1500 started
Starting modem test...modem.begin() succeeded
AT+IPR?
+IPR:115200 
OK
===> ['#' char sent] <===
Changing baud rate
AT+IPR=460800
ERROR
changed to 460800
===> ['%' char sent] <===

Restore to 115200
AT+IPR?
+IPR:115200 
OK

Like the modem SIM7600, it appears the SARA R4 is pretty useless for ftp transfers (low baudrate and no REST command). The only solution I have, it to reinvent the wheel by using sockets directly.

2

Whar kind of data do you want to send? If you want to send collected data, take MQTT, FTP is somehow the wrong protocol for a Arduino IMHO

3

I want to send images (500kB). About 50MB/day. I use a custom board with atmega1284P, not Arduino.

After contacting the SIMCOM company, they made me realize that the 4G module I received (from my french local distributor) was not designed for Europe. I order a new DRobot 4G module based on SIM7600G-H and it looks ok now.
"G" for global. But "E" should be fine as well.

So I let the SARA R4 and switch back to the SIM7600 module.

4

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