Week-12 @RTEMS-GSoC-2025

Overview

This week, I completed the following tasks :

• Work on pbuf allocation for RX BDs
• Testing RX test

Work completed this week

1. Work on pbuf allocation for RX BDs
   • Worked on formulating mechanism for allocation of empty pbufs, to be filled by data received, for GRETH RX
   • GRETH requires pbufs with at maximum, 1514 bytes. So I tried allocating 32 pbufs of size 1514 bytes and attaching each to a single BD.
   • However, the actual allocation revealed that 31 pbufs of size 1516 bytes got allocated while last pbuf was of size 1452 bytes.
     
   • The pattern was like 2 extra bytes got allotted to each pbuf and this accumulated to allocation of 2*31 = 62 bytes less than 1514 (the targetted size) to last BD (i.e. 1452 bytes).
   • I tried allocationg some different sizes, and got the following results :
     • Using 1500 bytes, 1500 bytes allocated to each pbuf
     • Using 1502 bytes, 1504 bytes allocated to each pbuf
       This trend suggested that lwIP internally rounded the memory size to a memory alignment of 4 bytes
   • I also learnt that for getting the size of 1514 bytes I would need to set the macro MEM_ALIGNMENT to 2 instead of 4, which it was right now. SO keeping a size of 1516 bytes is optimal.
2. Testing RX test
   • Initially, on running the test, ARP response was being generated and sent correctly, however, ARP replies weren’t getting generated by the GRETH driver.
   • Hence, I switched to using lwIP debugging using

      [sparc/leon3]
      LWIP_DEBUG=LWIP_DBG_ON
      API_MSG_DEBUG=LWIP_DBG_ON
      ETHARP_DEBUG=LWIP_DBG_ON
      IP_DEBUG=LWIP_DBG_ON     
     

     options in a new file - config.ini, in rtems-lwip source tree. Building RTEMS lwIP package with this helped use several debug options while running the tests tx_udp.exe and rx_udp.exe with much more information, like the IP HEADER, various internal function calls, etc.

   • Using a .ini file is very useful since configuration of several BSPs can be written together at a single place.

Plans for next week

1. Work on gettig expected results from GRETH lwIP driver RX mechanism