IXP1200 Ready Bus Sequencer

[Tammo Spalink]

I am pretty sure I deal with stale flags correctly.

What I was hoping for is an example set of 12 sequencer instructions
that are known to work well for my scenario: 8x100Mb, no autopush.

Tammo

On Tue, 19 Sep 2000, "Paige, Dale W" wrote:
> A commonly encountered problem can be encountererd when the ready bus
> sequencer is servicing "slow ports" (10/100 ports).  The collection of the
> ready flags is asynchronous with the operation of the IX Bus receive state
> machine.  You can read the ready flags and find flags that are set even
> though a rcv_req has been queued or even completed for the port indicating a
> need for service.  This is due to the latency in handling the ready receive
> requests.  Imagine a ready bus rxrdy command collecting the flags the IX Bus
> cycle before the MAC de-asserts its RxReady signal for the port which is the
> subject of an IX Bus read.  We refer to such flags as stale flags.
> 
> To deal with stale flags the RxReady flags can be "aged" by holding them for
> one or two ready bus sequencer cycles before using them and AND'ing them
> with the inverse of a "rcv_req outstanding" bit map.  The RCV_RDY_CNT
> associated with a set of RxReady flags is generally used to assist in this
> purpose, although the RCV_CNTL_CNT can be used for an even more precise (yet
> computationally intricate) tracking of the state of the RxReady flags.
> Refer to the Hardware Reference manual section 6.6.4.8, "Interpreting The
> Receive Ready Flags", for more information.
> 
> On the transmit side you want to read the TxReady flags fairly frequently so
> your transmit process can proceed as quickly as possible.