3 Replies Latest reply on May 15, 2017 12:29 PM by Carlos_A

    Intel 82579LM Gigabit Phy & QM77 PCH - TCTL register and Tx functionalities

    Tweety Community Member



      I'm working on the Intel 82579LM Gigabit Ethernet PHY linked to a QM77 PCH - 7/C210 Series Chipset.

      (I'm not really sure if this topic is supposed to be in software/BIOS or in hardware section)


      • When activating the Ethernet Tx functionalities, using the TCLT register ( p186 of Intel® 82579 GbE PHY: Datasheet, Vol. 2.1, § ),
        I noticed that there is a "Reserved" "Read only" bit 28 set to '1' by default.
        However, this bit doesn't seem to be read-only, as it can be written. And if this bit is not specifically set to value '1', the Tx functionalities do not work.
        Although I agree it is not "best-practice" to set "Reserved" bits, is this behavior normal ?



      Many thanks !

        • Re: Intel 82579LM Gigabit Phy & QM77 PCH - TCTL register and Tx functionalities
          Carlos_A Brown Belt

          Hello, Tweety


          Thank you for contacting Intel Embedded Community.


          In order to better understand this situation, could you please tell us if your previous questions are related to a technical issue? In case that your answer is affirmative, please give us a detailed description of this problem.


          Thanks in advance for your collaboration.


          Best regards,


            • Re: Intel 82579LM Gigabit Phy & QM77 PCH - TCTL register and Tx functionalities
              Tweety Community Member



              Well it's not really a technical question about something not working, more an interrogation about the data sheet and my understanding of it.



              For the second point in my first topic, not much to say, there are just no info on the data sheet about bit 25 of CTRL reigster.

              However, there are references about bit CTRL.SU (for instance in explaination of bit of STATUS register), which is no where to be found.

              So is bit 25 of CTRL register the "CRTL.SU" bit ?



              For the first point, I initialized the 82579LM following the standard initialization process of Ethernet controllers

              (as explained in the Intel I211 Ethernet controller, Intel 82579 Gigabit Ethernet controllers datasheets and in the Intel open source PCIe Ethernet Gigabit software manual)

              Reset, disable interrupts, disable flow control (in my case), enable auto-negotiation, clear statistics and MTA registers,

              Initialize descriptor rings for transmission & reception, set reception/transmission ring related registers and enable reception/transmission.


              The 82579LM worked fine in reception, but couldn't send Ethernet frames. So I checked the TCTL register (in charge of TX functionalities)

              To set the TCTL register, I just put the fields that were of interest for me (PSP, COLD, TCTL and EN fields, in the data sheet) to a certain value, zero-ing the rest.

              • The bit 28 of TCTL, reserved, supposed to be set to '1' and read-only, was set to '0' during this process.
                To me 'read-only' means someone is not supposed to be able to set it to any value.
                So I was wandering whether it was my interpretation of read-only, or it was the data sheet that was wrong.
              • If this bit 28 of the TCTL register is not set to '1', the emission can't work (I tried toggling it to 1/to 0, and it is really the only thing I found)
                Since there are no notes about this bit, I was also wandering if this was normal