How to configure and ping Ethernet on STM32

This tutorial is the start of the Ethernet series in STM32. Today we will simply see how to configure the Hardware.

For some of the MCUs, this will be as easy as the default setup, but for others, this part could be very complicated. Specially the Cortex M7 Series MCUs, where the cacheable region causes data coherency issues.

So I will try to explain the process in the best possible way. To better understand the result of different settings, I would suggest you to watch the Video at the end of this post.

CubeMX Configuration

After enabling the Ethernet, you must cross check the pins configured by the cubeMX with the schematic of the board. Most of the times, the pins are configured incorrectly and it becomes one of the most popular error for the ethernet to not work.

Ethernet Configuration

There are many types of configurations available with different MCUs. Some MCUs let you configure the memory in the CubeMX, while others don’t. Some of the Boards have the MII Hardware, while other have RMII.

Below is the picture showing different configuration available in different ST Boards.

• The First board (Nucleo F207ZG) and second board (Disco F7508) uses the RMII pinout, while the third board (Disco H745) uses the MII pinout.
• On the first board we have the option to choose the PHY Address. This should be set to 0, if you are using the on board LAN Port, and it should be 1 in case of the external module.
• The 2nd and 3rd boards allow us to configure the memory addresses while the first one does not. If your board does not allow the memory configuration, you can simply skip those steps.
• The H745 discovery board is letting us configure the addresses for Tx and Rx DMA descriptors, and for the Rx Buffer as well. But the F7508 Discovery board does not let us configure the address for the Rx Buffer.
• Assuming that each DMA Descriptor takes 32 bits (MAXIMUM Possible), the RX Descriptor and Tx Descriptor have a maximum size of 128 Bytes (32×4) each.
• The Memory between them is spaced keeping this 128 bytes in mind.
• The Rx Buffer length is set to 1524 Bytes, but the number of RX buffers to be used can be defined later in the LWIP configuration. By default the cubeMX sets the number to 12 buffers. This would make the total length of Rx Buffer around 18KB.
• The memories are allocated in the SRAM region, whose properties can be modified later in the MPU.

LWIP Configuration

The LightWeight IP can be enabled in the middleware section. If the MCU does not let you enable it, make sure the cache (DCache and ICache) are enabled.

The most of the Configuration in the LWIP remains same. Except, some MCUs let us choose the address for the Heap.

• Here we are going to disable the DHCP, and configure a static IP for our ethernet module. I have set the IP 192.168.0.123 for the board.
• In the Key Option tab, I am using 5KB memory for the Heap. The location for this heap is defined as 0x30004000.
• In the Platform Settings tab, set the PHY as LAN8742.

MPU Configuration

We have the DMA Descriptors in the SRAM Region. This is why we need to configure the MPU.

If your MCU didn’t let you choose the memory region, then probably you don’t need to do it. But for the cortex M7 devices, this is a must, or else you will get hardfault.

Remember that during the configuration, we set up everything in the SRAM (0x30000000). The complete memory structure is shown in the image below.

Below is the image showing the MPU configuration for the above Region.

• Here I have selected the 32 KB region so that it will cover our total RAM region, which is around 24KB.
• The rest of the configuration is to set the region as non-cacheable region.
• This would prevent the cache coherency issue between the CPU and the DMA.
• This is explained in the cortex M7 playlist, so do check that out.

Other Configuration

If you are connecting the STM32 board to the Router, there is nothing you need to do at the computer end. But if you are connecting the ethernet cable directly to the computer, you need to configure your computer’s ethernet as per the images shown below.

Below is the configuration for a Windows computer.

Below is the configuration for Mac.

The CODE

Once the project is generated, open the LWIP -> Target -> ethernetif.c file. Here you will some memory locations that needs to be defined in the flash script file.

We need to define these memory locations in the flash script file, as per the configuration done in the cubeMX.

Below is the code is for the H745 Discovery board according to the configuration done in the cubeMX.

    .lwip_sec (NOLOAD) : {
    . = ABSOLUTE(0x30000000);
    *(.RxDecripSection) 
    
    . = ABSOLUTE(0x30000080);
    *(.TxDecripSection)
    
    . = ABSOLUTE(0x30000100);
    *(.Rx_PoolSection) 
  } >RAM_D2

Below is the code is for the F7508 Discovery board according to the configuration done in the cubeMX.

    .lwip_sec (NOLOAD) : 
  {    
    . = ABSOLUTE(0x2004C000);
    *(.RxDecripSection) 
    
    . = ABSOLUTE(0x2004C0A0);
    *(.TxDecripSection)
  } >RAM

The main file

Since this tutorial is more focused on connection part, there is not much in the code. We will just test the ping to our IP Address, and the code for the same is shown below.

extern struct netif gnetif;

int main()
{
  int wait = 10000000;
  while (wait-- >0);  // Wait for sometime before initializing the system
  
  MPU_Config();
  SCB_EnableICache();
  SCB_EnableDCache();
  HAL_Init();
  
  HAL_Delay (1000);  // wait for some time here
  
  SystemClock_Config();
  MX_GPIO_Init();
  MX_LWIP_Init();
  while (1)
  {
     ethernetif_input(&gnetif);
     sys_check_timeouts();
  }
}

RESULT

Below is the result from the ping test.

You can see the ping is working on the IP Address that we set during the configuration.