RE: [ethmac] hi

["Illan Glasner" <iglasner@zumanetworks.com>]

17-Apr-01

   Hi,

   First flow-control is for full duplex only and it is suppose to do
the same thing backpressure to in half-duplex.

the idea behind the back-pressure is that if you station have all the
Rx-FIFO's full and can't recive and more data it will start
back-pressure meaning basicly make collision to avoid the other station
from sending the data.

in flow control the mechnisem is based on telling the other side how
much time he need to be silent which is 16 bit number where each number
equal one slot time (512BT), however almost all application simeple use
it in the on/off mechnisim meaning when they full they send the value
FFFF and as soon as they are ready they send the number 0000.

You will also need to consider the case when you start sending max size
packet and the other side send you min size packet and you become full
than if you wait till the end of the packet you started sending you will
get about 30 more packets in the meantime and of course there are few
solution for this, just something to be aware of incase you wern't.

one thing you might want to be aware of is that almost all modern system
shut off the backpressure/flow-control as the usefull ness of it is not
as was through at the begining and it have some major drawback so my
advise is make it with enable/disable capability.

have a nice day

   Illan


-----Original Message-----
From: suresh.dorepally@st.com [mailto:suresh.dorepally@st.com]
Sent: Monday, April 16, 2001 7:40 AM
To: ethmac@opencores.org
Subject: [ethmac] hi


Dear all,
Can anybody please explain the implementation of the Backpressure or
flow
control in half duplex mode.
Thanks in advance.

BR,
Suresh