4 Replies Latest reply on Jun 23, 2011 2:43 AM by Enric

    GCU Config



      I was loking at the GCU config register in the EAS file and it seems to have a typo.

      In page 16 it says that bits 25:19 are the router clock ratio setting and 18:12 the tile clock ratio.

      It seems to me from tables 4 and 5 that it is the other way round. Please tell me if I'm wrong.


      On the other hand I was wondering about the router clock frequency set. What value is followed, the one that we set in the initialization or it changes when we modify it in the GCU register?


        • 1. Re: GCU Config

          The tables look fine to me; but admittedly interpreting them is not straightforward.


          For example, consider Table 4.

          • The global clock is 1.6 GHz. It always is.
          • The router clock is the global clock/(router clock divider setting + 1).
          • The tile clock is the global clock/(tile divider setting +1).

          So, consider the second line of Table 4.


          router clock = 1.6 GHz/(1+1) = 800 MHz and tile clock = 1.6 GH/(2+1) = 533 MHz.


          Please think about the clock crossing FIFO. The router is 2xglobal and the tile is 3xglobal. So you want 3 router "chunks" for every 2 tile "chunks". The common whole number is then 6. We actually use 7 for safety. So the router clock ratio is then 7x(3 router chunks) = 21.


          Bits 25:19 for the second line in the table (the 533 line) are 00 10101 .... which is 15(hex) which is 21. Bits 18:12 are the tile clock ratio, which is 7x(2 tile chunks) = 14. The bits are 000 1110  = 0e(hex) = 14(dec). Bits 25:08 are 00 1010 1000 1110 0010, as shown in the table.

          • 2. Re: GCU Config

            Now consider table 5. I'll pick the third line.

            400     00 1110 0000 0111 0011


            • The global clock is still 1.6GHz.
            • The router clock is the global clock/(router clock divider setting +1)
            • The tile clock is the global clock/(tile divider setting +1)


            router clock = 1.6GHz/(0+1) = 1.6GHz and tile clock = 1.6Ghz/(3+1) = 400 MHz.


            The router is 1xglobal and the tile is 4xglobal. We want 4 router "chunks" for every 1 tile "chunk".

            Then, using the 7 (as before), the router clock ratio setting is 7x4 = 28, which is 1c(hex). Bits 25:19 are 00 1110 0, from the table.


            Also, the tile clock ratio is 7x1 = 7. Bits 18:12 are 000 0111.

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            • 3. Re: GCU Config

              About the router clock... it's not meant to be changed through the GCU.  We intended the GCU to be for users to directly change the tile frequency. SInce you have the possibility of two different router clocks, depending on how you last trained, we provided two tables.

              • 4. Re: GCU Config

                Thank you,

                Now it has more sense