As a followup to my previous post on adding support for Olimex STM32-E407 to Mbed OS, I have created a tutorial on how to setup and run a basic networking example with the offline Mbed CLI.

Prerequisites

• git
• mercurial
• python3
• dfu-util

Python 2.7.x is mentioned in docs as of 2019-10-19, but I have used Python3 and it works fine for me. As Python 2 is not maintained past 2020, we will use Python3.

On Ubuntu you can install the prerequisites with the following command

sudo apt install python3 python3-pip git mercurial dfu-util

Installation

NOTE: Mbed recommends you install mbed-cli in an virtual environment (like virtualenv) but I have installed it globally for convenience and laziness.

sudo pip3 install mbed-cli

Next, we need to install a compiler for ARM. I chose GCC ARM

NOTE: installing gcc-arm-none-eabi using via apt package repositories is NOT recommended

Download the toolchain from https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-rm/downloads

Install the toolchain to /opt (or somewhere else)

cd ~/Downloads
tar xvf gcc-arm-none-eabi-8-2019-q3-update-linux.tar.bz2
sudo mv gcc-arm-none-eabi-8-2019-q3-update-linux /opt
sudo ln -s /opt/gcc-arm-none-eabi-8-2019-q3-update-linux /opt/gcc-arm-none-eabi

Configure Mbed to use your toolchain

mbed config --global GCC_ARM_PATH /opt/gcc-arm-none-eabi/bin

Setup Mbed CLI

Create a new project

mbed new ethernet-example
cd ethernet-example

You will need to update to Mbed 5.15.0 or later (you can tell if STM32-E407 support is present by running find mbed-os/targets/ -iname "*OLIMEX*")

cd mbed-os
# checkout the commit where STM32-E407 was merged to master
mbed update latest
cd ..

Create main.cpp inside the ethernet-example/ directory with the following code:

#include "mbed.h"
#include "EthernetInterface.h"

// Network interface
EthernetInterface net;
DigitalOut led1(LED1);

// Socket demo
int main() {

    // LED on while the request is being made
    led1 = 0;

    // Bring up the ethernet interface
    printf("Ethernet socket example\r\n");
    net.connect();

    // Show the network address
    const char *ip = net.get_ip_address();
    printf("IP address is: %s\r\n", ip ? ip : "No IP");

    // Open a socket on the network interface, and create a TCP connection to mbed.org
    TCPSocket socket;
    socket.open(&net);
    socket.connect("www.arm.com", 80);

    // Send a simple http request
    char sbuffer[] = "GET / HTTP/1.1\r\nHost: www.arm.com\r\n\r\n";
    int scount = socket.send(sbuffer, sizeof sbuffer);
    printf("sent %d [%.*s]\r\n", scount, strstr(sbuffer, "\r\n")-sbuffer, sbuffer);

    // Recieve a simple http response and print out the response line
    char rbuffer[64];
    int rcount = socket.recv(rbuffer, sizeof rbuffer);
    printf("recv %d [%.*s]\r\n", rcount, strstr(rbuffer, "\r\n")-rbuffer, rbuffer);

    // Close the socket to return its memory and bring down the network interface
    socket.close();

    // Bring down the ethernet interface
    net.disconnect();
    printf("Done\n");

    // LED off
    led1 = 1;
}

The code basically sets up an Ethernet connection using DHCP to obtain an address, then creates an HTTP request to www.arm.com, reads the response, then closes the connection and Ethernet interface.

Compiling

mbed compile -t GCC_ARM -m OLIMEX_STM32E407_F407ZG

Programming

Set the STM32-E407 board to DFU mode (move jumper B0_1 / B0_0 to B0_1 position)

Then run the following command to flash the board

sudo dfu-util -a 0 -s 0x08000000 -D BUILD/OLIMEX_STM32E407_F407ZG/GCC_ARM/ethernet-example.bin

Running

The following is required to see the output

• Disable DFU mode (B0_1 -> B0_0)
• Connect a serial port to the BOOT header (pinout is on the back of the board)
• Connect an Ethernet cable from the board to your network.
• Open the serial port at 9600 baud. On Linux I use picocom like so:

sudo picocom -b 9600 /dev/ttyUSB0

• Push the RESET button (by the DC barrel connector) to boot the code

You should get something like this on the serial port

IP address is: 10.42.0.193
sent 38 [GET / HTTP/1.1]
recv 64 [HTTP/1.1 301 Moved Permanently]
Done

Congrats you have Mbed OS running on the STM32-E407!

Changing the serial port baud

By default, stdout is written to USART3 on PB10 / PB11 at 9600 baud. If you want to use another port or baud rate for debugging (such as the UART on the UEXT header), add the following to mbed-app.json in the project directory.

{
    "target_overrides": {
        "OLIMEX_STM32E407_F407ZG": {
          "target.stdio_uart_tx": "PC_6",
          "target.stdio_uart_rx": "PC_7",
          "platform.stdio-baud-rate": 115200,
          "platform.default-serial-baud-rate": 115200
        }
    }
}