appended below is an email from david mcmahon that's
needed/recommended for instruments that use xaui links to send
data from one board to another, where these boards are run off the same
clock,
sending data synchronously from one board to the other.
most of the large instruments we are developing are globally asynchronous
(eg: the packetized correlator, where data is time stamped, and data
links and boards run asynchronously) - these instruments won't have
this problem,
and no fix is needed.
however, there are several instruments that will/might benefit from
the technique that david and oren figured out:
ATA beamformer (oren implemented the fix already)
seti spectrometer
SMA beamformer
ibob/bee2 systems glen jones is developing?
ibob/bee2 systems at nrao?
dan
David MacMahon wrote:
It's more to do with interfacing with the yellow blocks where the
sender and receiver have the same clock. In that case, it is OK to
drive rx_get with a '1' (i.e. "give me a sample every cycle"), but in
order to avoid running the async fifo on empty, which risks
underflowing the fifo, rx_get should be driven with an inverted and
delayed version of the "rx_empty" signal. This defers assertion of
rx_get until some number of cycles after the fifo gets its first
sample, which allows the fifo to run a little above empty, which
provides the buffering needed to ensure that the burstiness of the
async protocol doesn't lead to fifo underflows.
Dave
On Jun 5, 2008, at 11:02 , Dan Werthimer wrote:
dave,
what's the "improvement to bee2 xaui links"?
(in matt's email below)
anything we should use?
thanks,
dan
Here are a few updates...
BEE2s
Oren, Dave, ... have made major improvements in the BEE2 XAUI links.
