Using LwIP on the STM32H7

[Robin Müller]

Some clarification: The linker script used for RTEMS is of course the
default RTEMS linker script, the FreeRTOS example used the linker file
taken from the STM32CubeH7 repository.

Kind Regards
Robin Müller

On Thu, 28 Jan 2021 at 14:35, Robin Müller <robin.mueller.m at gmail.com>
wrote:

> Hi,
>
> I am trying to get LwIP working on the STM32H7 because it has a low RAM
> usage (at least that's what I heard). We already did this for FreeRTOS, but
> we used the LwIP Raw API to not be bound specifically to the OS. I am now
> trying to adapt LwIP to RTEMS , but I'm not really a LwIP expert and most
> did copy & paste up until now.
>
> So far, transferring the code has worked, but there are some specific
> sections in the code used for our FreeRTOS example which put the ethernet
> DMA descriptors in specific sections:
>
> ETH_DMADescTypeDef DMARxDscrTab[ETH_RX_DESC_CNT]
> __attribute__((section(".RxDecripSection"))); /* Ethernet Rx DMA
> Descriptors */
> ETH_DMADescTypeDef DMATxDscrTab[ETH_TX_DESC_CNT]
> __attribute__((section(".TxDecripSection")));   /* Ethernet Tx DMA
> Descriptors */
> uint8_t Rx_Buff[ETH_RX_DESC_CNT][ETH_RX_BUFFER_SIZE]
> __attribute__((section(".RxArraySection"))); /* Ethernet Receive Buffers */
>
> /* For RTEMS can we put this in the text section? */
> //ETH_DMADescTypeDef DMARxDscrTab[ETH_RX_DESC_CNT]; /* Ethernet Rx DMA
> Descriptors */
> //ETH_DMADescTypeDef DMATxDscrTab[ETH_TX_DESC_CNT];   /* Ethernet Tx DMA
> Descriptors */
> //uint8_t Rx_Buff[ETH_RX_DESC_CNT][ETH_RX_BUFFER_SIZE]; /* Ethernet
> Receive Buffers */
>
> I got an "section `.unexpected_sections' will not fit in region
> *   `UNEXPECTED_SECTIONS'" error because of this. I checked the linker
> script used, which was taken from the STM32CubeH7 repository and found this
> LwIP specific section:
>
>   .lwip_sec (NOLOAD) : {
>     . = ABSOLUTE(0x30040000);
>     *(.RxDecripSection)
>
>     . = ABSOLUTE(0x30040060);
>     *(.TxDecripSection)
>
>     . = ABSOLUTE(0x30040200);
>     *(.RxArraySection)
>   } >RAM_D2 AT> FLASH
>
> So the descriptors are placed at RAM_D2 (or SRAM_3 in RTEMS). I've placed
> the following
> section in linkcmds.base now:
>
>     .lwip_sec (NOLOAD) : ALIGN_WITH_INPUT {
>         . = ABSOLUTE(0x30040000);
>         *(.RxDecripSection)
>
>         . = ABSOLUTE(0x30040060);
>         *(.TxDecripSection)
>
>         . = ABSOLUTE(0x30040200);
>        *(.RxArraySection)
>   } >SRAM_3 AT> REGION_TEXT_LOAD
>
> Are any STM32 or LwIP experts here that see a problem with this adaption?
> I still need to do some other stuff to integrate LwIP properly so I haven't
> tested it yet. Are there any other thinks I need to take into account for
> making LwIP work with RTEMS?
>
> Kind Regards
> Robin
>
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