Hi, anybody,
I am using STM32F407ZG/STM32F429IG to build two similar control board. The main function is
some host send amount of data, about 1M bytes (STM32F407 with FSMC/SRAM) or 32M bytes (STM32F429 with FMC/SDRAM)
to STM32 and stored in memory. Then after some control command, the STM32 MCU control GPIOs
to drive another board. The problem is: both STM32F4 MCU claim that they have up to 100M bps
transmit speed, but I only got about 100 kbps.
The base code is generated with STM32CubeMX, enabled FreeRTOS with CMSIS_v2 API, LwIP (2.1.2) and mbedTLS (used for encrypt).
firmware is STM32Cube_FW_F4_V1.25.2, PHY is LAN8720A. And I config three task:
1. default task with 1024 words stack size for TCP handling
2. idle task which has low priority to broadcast MCU's IP and port (IP is DHCP supplied) through UDP, which is blocked by a binary semaphore when a TCP connection is accepted.
3. a realtime task for GPIO transmit, which is downgrade to normal priority for testing (empty task with osDelay now)
I have Googled around, and most tips are about sending throughtput, seems receiving are talked little.
[Low TCP/IP transmit perormance with STM32CubeMX and STM32F429ZG](https://community.st.com/s/question/0D50X00009XkZaV/low-tcpip-transmit-perormance-with-stm32cubemx-and-stm32f429zg)
talks about memcpy performance, but in testing scencio, I even do not use FSMC/FMC memory. But I changed
the memory map:
1. all code and RW ZI data are moved into CCM for better performance
2. ethernetif, lwip, mem, memp are keeped in SRAM 1 start with 0x20000000 for DMA accessable
3. SRAM 2 start with 0x2001C000 left for other purpose.
I use netconn API built a req/rep pattern server on MCU. When payload data is less than TCP_MSS,
it is fast enough, but when I send a 32 kbytes data block, it slows down.
I have enlarged the TCP_MSS to 1460, and TCP_WND to 11*TCP_MSS. All other tries are failed.
The last day's experiment show that: when I do some printf inside low_level_input to check the incoming
packet info, the performance suddenly run up to 500 kbytes/s, aka 4 Mbps. It is Incomprehensible, and seems
fail into quantum domain :(. I also tried sprintf and other method to check incomming packet info, but no lucky.
So how could I touch the 100Mbps?
