lib_ethernet thread rgmii_10_100_master_tx_pins causes random delays

Technical questions regarding the XTC tools and programming with XMOS.
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Joined: Thu Sep 15, 2011 7:19 pm

lib_ethernet thread rgmii_10_100_master_tx_pins causes random delays

Post by aritec »

Using lib_ethernet with RGMII interface causes random sending delays up to 21s.
The reason for this is on the rgmii_10_100_master_tx_pins task:

Code: Select all

       int word_count = byte_count >> 2;
        tail_byte_count = byte_count & 3;

        // Ensure that the interframe gap is respected
        tmr when timerafter(ifg_time) :> ifg_time;

        // Send the preamble
        {tmp1, tmp2} = zip2(0x55555555, 0x55555555);
ifg_time is calculated at the end of the last sent buffer.
If there is a idle time between buffers for more than 21 seconds, the timerafter(ifg_time) adds another (up to 21 seconds) delay before handling the buffer!
tmr is a 2^32 bit 100MHz counter but timerafter() can only handle delays up to 2^31 ticks. Longer delays are handelt after a "rollover" after 42 seconds.
As a work around, I restricted the max idle time to 20 seconds with this hack:

Code: Select all

unsafe void rgmii_10_100_master_tx_pins(streaming chanend c,
                                 out buffered port:32 p_txd,
                                 streaming chanend c_speed_change)
  unsigned tmp1, tmp2;
  timer tmr;
  unsigned ifg_time;
  unsigned TimerWorkaround;
  tmr :> ifg_time;

   while (1)
    uintptr_t buffer;
    unsigned timestamp;

   TimerWorkaround = 0;
      case c_speed_change :> buffer:
      case c :> buffer:
      case tmr when timerafter(ifg_time + 2000000000) :> ifg_time:
        TimerWorkaround = 1;

    unsigned int eof_time;
    int tail_byte_count;

    mii_packet_t * unsafe buf = (mii_packet_t * unsafe)buffer;

  if (TimerWorkaround == 0)
      unsafe {
        register const unsigned poly = 0xEDB88320;
        // Pre-load CRC with value making equivalent of doing crc of ~first_word
Might be helpful for other lib_ethernet / lib_xtcp users, if there are any out there ;-)
Best regards
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Joined: Thu Dec 10, 2009 9:20 pm
Location: Bristol, UK

Post by Ross »

Thanks for the post, please consider raising an issue on :)
Technical Director @ XMOS. Opinions expressed are my own.