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[lwip-users] CRC of each IP Header is not calculated after some point (S

From: Michael Steinecke
Subject: [lwip-users] CRC of each IP Header is not calculated after some point (STM32F4)
Date: Tue, 23 Sep 2014 01:02:37 -0700 (MST)

Hello Folks,

its me again. I've discovered another strange behavior with the STM32F429ZG
device in conjunction with LwIP 1.4.1 (and FreeRTOS). Everything goes
smoothly for some time, several transfers and so on. But from one point on,
the CRC calculation for all outgoing packets fails or is not executed
In the attached pcap file, I've transferred the same file (~10 MB) from
SD-Card several times. Beginning with packet 452 every outgoing IP Header
has a checksum of zero. Eventually every packet gets discarded by PC. Then
with packet 463, the PC sends another command. The MCU tries to ACK it, but
still no CRC. Conclusion: CRC on receive either works or ist not checked by
After the RST from PC, the MCU falls back in auto discovery state. For that,
TCP data port 55557 gets closed and a new accept() socket with the same port
is initiated.
Now we can see a lot of UDP 55555 and DHCP discovery broadcasts. Each of
them with the same problem.
After a reset of the device, everything is working smoothly again.

CRC calculation is done by HW (SW calculation in LwIP turned off), therefore
I would expect another STM bug. Is there something known? Some ideas how to
track down this?


Turn on checksum calculation in Wireshark. (UDP/TCP settings)

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