[hpsdr] What can we do with 2 cards

[Bill Tracey]

When we started down this path with the Xylo I think one of the 
configuration goals we had was:

         1. Sound Card replacement
         2. Ultra Low Latency CW input
         3 .SDR 1000 Parallel Port Control

As we morphed to HPSDR my hope was that this configuration could be done 
with two cards - Audio (Janus) and USB/FPGA (Ozy)

At the moment it looks like we may only be able to do #1 with 2 cards.  We 
might be able to do #1 & #2 if we can get low latency CW keying via I2C I/O 
via FX2.    We certainly cannot do #3 with just 2 cards.  At the moment on 
the Xylo prototypes we've got PTT/DOT and DASH coming thru FPGA pins and 
their state gets integrated into the audio data stream going to the radio, 
giving very low latency..  Doing CW via I2C via FX2 may have sufficiently 
low latency, not sure of this.  I'd assume we'd have to read from an FX2 
USB endpoint to get the status of the ports -- anyone know if one can do a 
blocking read waiting for the state of the I2C ports to change from the PC 
-- hate the idea of having to poll the USB port at a hi rate for good CW 
performance.       I don't think we can do SDR 1000 parallel port control 
with the I2C expander as it takes 17 (D0-7, C0-3, S3-S7)  lines, also not 
clear to me  how quickly we can and need to wiggle those lines to program 
the DDS in the SDR 1000 when going via an I2C.

One idea to get back to doing dot/dash directly thru the FPGA is to go 
through the Janus.  It looks like there are 4 unused I/O on the Janus 
CPLD.  Could we add some protection circuitry on the Janus to 2 of those 
lines and configure the CPLD to put those sigs on the Atlas bus.   Maybe 
add 3 more pins to the 0.100 unbalanced audio connector?

I that's not  viable, is there space for protection circuitry for 2 lines 
on the Ozy  and a 3 pin connector?  Could we jumper the configuration of 
the FPGA serial port such that it's either tied to the level converter or 
the external connector?

Just some late night thoughts -- trying to find a way to get a little more 
function into a 2 board setup.

Regards,

Bill (kd5tfd)





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