LwIP simply layers on top of the underlying transport code.
Look at how it dispatches frames.
Most of the HAL library is considered self-documenting
STM32Cube_FW_F4_V1.25.0\Drivers\STM32F4xx_HAL_Driver\Src\stm32f4xx_hal_eth.c
HAL_ETH_TransmitFrame()
STM32Cube_FW_F4_V1.25.0\Projects\STM324x9I_EVAL\Applications\LwIP\LwIP_IAP\Src\ethernetif.c
low_level_output(struct netif *netif, struct pbuf *p)
>>.. i find it very difficult to acquire resources online
Unfortunately support has no perceived value anymore..
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