Reinitialization of stm32f driver problem

[PaulFirs]

Issue with descriptor counter not resetting on driver reinitialization

Problem Description

• My goal is: To be able to reinitialize the Mongoose TCP/IP stack (mg_mgr and mg_tcpip) without losing network connectivity, specifically to change IP address at runtime.

• My actions were:

  1. Started application with stm32f driver using default 4 descriptors (ETH_DESC_CNT = 4)
  2. Sent a single ping to the device (incrementing TX descriptor counter s_txno from 0 to 1)
  3. Called reinitialization sequence:

     mg_mgr_free(mgr);
     mg_mgr_init(mgr);
     mg_tcpip_init(mgr, ifp);

• My expectation was: After reinitialization, the network stack should work correctly with the new IP address, and ping should work normally.

• The result I saw:

  • Ping stops working correctly after reinitialization
  • Either no ping responses, or very high latency values
  • RX interrupt logs show multiple packets arriving simultaneously/incorrectly
  • However, if I ensure the last ping arrives when s_txno == (ETH_DESC_CNT - 1) before reinitialization, then reinitialization works correctly and device is pingable at the new IP

• My question is: This doesn't seem like normal driver behavior. Is it a bug or is there something I'm missing?

Root Cause Analysis

The static variables in mg_tcpip_driver_stm32f.c are not reset during reinitialization:

static uint8_t s_txno;  // Current TX descriptor - NOT RESET on reinit
static uint8_t s_rxno;  // Current RX descriptor - NOT RESET on reinit

When hardware Ethernet MAC is reset (via RCC->AHB1RSTR), DMA descriptors are cleared to initial state, but the software counters retain their old values, causing mismatch.

Reproduction Steps

1. Initialize Mongoose with stm32f driver
2. Send one ping (s_txno becomes 1)
3. Call reinit sequence without resetting s_txno/s_rxno
4. Try to ping - fails or behaves incorrectly
5. Alternatively: ensure s_txno == 3 before reinit - works correctly

Workaround

The issue resolves if descriptor counter happens to be at maximum value before reinit, suggesting the counters need explicit reset.

Environment

• Mongoose version: 7.19
• Compiler/IDE and SDK: ARM GCC, VSCode
• Target hardware/board: STM32F407 / STM32F765
• Connectivity chip/module: Built-in STM32 Ethernet MAC with LAN87x PHY
• Target RTOS/OS: FreeRTOS

Proposed Solution

Add static variable reset in mg_tcpip_driver_stm32f_init():

static bool mg_tcpip_driver_stm32f_init(struct mg_tcpip_if *ifp) {
  // Reset static counters on reinitialization
  s_txno = 0;
  s_rxno = 0;
  
  // ... rest of init code
}

Or provide a proper deinitialization function that resets driver state.

[scaprile]

That is not the way our stack works.
If you change your IP, you don't need to restart Mongoose, except for the fact that you have to close all open connections. The driver has not been thought to be reinitialized, that may or may not work, though your problem does not seem to be that. Just close all connections, as we do in several examples or at the top of the mgr_free code, or search for it at the Wizard Discord channel, or let me know and I'll post some.
If you change IP, you need to force a link down then link up for the stack to work properly. Since you are resetting everything but the PHY, the stack is not starting at link down, as it should.
Please see how we simulate Auto-IP in the TAP or pcap examples, and how we manage AP/STA switch in Wi-Fi examples.

We'll re-open this if necessary, closing for now, we can keep talking here.