STM32H7, LWIP and multi threading done right ?

[Manu Abraham]

Hi,

The more I am reading LWIP documentation, the more I get confused.

The entire LWIP codebase is scattered with #ifdefs making it look like a minefield and nightmare regarding maintainability. At least that's what I feel, maybe it is because I have not worked with LWIP before.

I see @Piranha​  citing clearly documented issues regarding CubeH7 package and multi threading regarding LWIP.

So, I have taken some interest to implement the code, the best possible way possible by me, based on LWIP documentation. But the more I look into it, I get even more confused.

To begin with, https://www.nongnu.org/lwip/2_1_x/multithreading.html

"How to get threading done right"

Did a search within the CubeH7 package regarding "LWIP_MARK_TCPIP_THREAD"

Searching 42199 files for "LWIP_MARK_TCPIP_THREAD" (case sensitive)

0 matches

@Amel NASRI​ @Imen DAHMEN​ After a few night outs, I have a splitting headache trying to sort things out. It appears as though the Cube H7 package is not really stable as far as Ethernet/LWIP is concerned.

I cant find even a single example, which properly implements LWIP guidelines, not even LWIP has sample code to describe the stack usage properly. It looks like a very poor stack regarding proper documentation too, forget maintainability and readability.

@Piranha​ Can you please point to at least a single properly implemented LWIP sample application code base ?

If anyone else has any pointers on this subject, please chime in even if it is 2c. I am all ears.

Thanks,

Manu

[Pavel A.]

ST's clone of LwIP repo is here.

LwIP has a mailing list: https://lists.nongnu.org/archive/html/lwip-users https://lists.nongnu.org/mailman/listinfo/lwip-users

If you're looking how to write asynchronously to a socket from which another thread reads,

see this question: https://lists.nongnu.org/archive/html/lwip-users/2020-04/msg00087.html

Note that FreeRTOS has their own TCP/IP stack, you may try it instead.

-- pa

[EmbeddedVito]

If yuu want to make your application thread safe you have to implement lwip multithreading.

The list of what to do that im going to show helped me resolving this problem: i wanted 5 thread calling the same function UDP_Server() (an UDP client created by me) every 1s. I always ended up in Hard Fault or problem related with memory in the LWIP library.

What to do:

• here you can read "See the example sys_arch.c files in unix and Win32 port in the contrib repository". the mentioned repository can be found here. You have to search for the file sys_arch.c inside the port folder. Choose the folder freertos. Inside this file you will see all the 4 functions mentioned about multithreading: sys_marc_tcpip_thread(), sys_check_core_locking(), sys_lock_tcpip_core() and sys_unlock_tcpip_core(). if you are working with CSIS RTOS you have to change the functions and put them inside your sys_arch.c file:

static osThreadId lwip_tcpip_thread;
static u8_t lwip_core_lock_count;
static osThreadId lwip_core_lock_holder_thread;
extern sys_mutex_t lock_tcpip_core;
 
void sys_lock_tcpip_core(void)
{
   if (lwip_core_lock_count == 0) {
     lwip_core_lock_holder_thread = osThreadGetId();
   }
   lwip_core_lock_count++;
   sys_mutex_lock(&lock_tcpip_core); //spostato sotto perchè in questa funzione si aspetta
}
 
void sys_unlock_tcpip_core(void)
{
	lwip_core_lock_count--;
	if (lwip_core_lock_count == 0) {
		lwip_core_lock_holder_thread = 0;
	}
	sys_mutex_unlock(&lock_tcpip_core);
}
 
void sys_mark_tcpip_thread(void)
{
	lwip_tcpip_thread = osThreadGetId();
}
 
void sys_check_core_locking(void)
{
	taskENTER_CRITICAL();
	taskEXIT_CRITICAL();
 
	if(lwip_tcpip_thread != 0)
	{
		osThreadId current_thread = osThreadGetId();
		LWIP_ASSERT("Function called without core lock",
				current_thread == lwip_core_lock_holder_thread && lwip_core_lock_count > 0);
	}

after doing this you have to put the declarations of these functions in your sys_arch.h and make LWIP_ASSERT_CORE_LOCKED and LWIP_MARK_TCPIP_THREAD (these macros are inside opt.h) points to sys_check_core_locked() and sys_mark_tcpip_thread()

• You have to declare the mutex lock_tcpip_core external inside your sys_arch.c (see line 4 of the previous code)
• you finally have to make LOCK_TCPIP_CORE and UNLOCK_TCPIP_CORE (inside tcpip.h file) pointing to sys_lock_tcpip_core() and sys_unlock_tcpip_core()
• the last thing you have to implement is a semaphore or mutex that will protect the ethernet to send a packet at time (ask if you want a detailed explanation)

[mak1308]

Hello, EmbeddedVito!

Can you give an example of using a mutex when sending a packet?

This is about the last point in your message: "the last thing you have to implement is a semaphore or mutex that will protect the ethernet to send a packet at time"

Thanks!