Re: Your Debian mouse problem

[Ramiro Aceves <ea1abz@xxxxxxxxx>]

I wouldn't recommend using anything less than a four layer board, 
since modern high-speed ICs expect power-supplies that are low 
impedance at high frequencies, with a ground plane and decoupling 
caps as close as possible to the device pins.  This is good for the 
chips, and helps to keep the power supply noise down.  (My earliest 
attempts at this stuff used wirewrap, which failed miserably!)

A ground plane also lets you use constant impedance traces for your 
signals.  I used a very handy tool ('Transmission Line 
Rapidesigner' - like a cardboard slide-rule) from National 
Semiconductor, which does the track width and spacing calculations 
for you.

Two other LVDS daisy-chains are used to program the HSP50016's and 
to receive the downconverted signals.  These are taken care of by 
the serial ports (SPORTs) on the Blackfin.  I plan to use the 
multichannel mode of the SPORTs to de-multiplex the phased array 
data, but I haven't come anywhere close to evaluating this yet.

The current problem is the TCP/IP code from Analog Devices.  The 
Blackfin hardware talks OK to my boards, but I'm having difficulty 
with sending packets from it to a host PC down the ethernet.  In my 
application the received signal is in the form of echoes, ie not 
continuous but bursty, so it lends itself to being packetised.  
After a few packets the code dies!  I'm wondering if the lwIP code 
that's bundled with the Blackfin (BF-537 EZKIT-Lite - $350 from 
Analog Devices) is really ready for the marketplace...  or is it my 
programming??

The Blackfin may seem like overkill for the ethernet link, compared 
to an FPGA solution, but I also plan to use it for waveform and 
control purposes in other parts of the application - if it can hack 
it!
73
Bob Stiles


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