gEDA-user: Trouble with an usb oscilloscope

["Robas, Teodor" <teodor.robas@xxxxxxxxx>]

Hello everybody,


I need some advice if there is somebody on this list and
has experience with ISP1581 chip or DMA buses.

Basically I made an usb based oscilloscope with the above
mentioned usb 2.0 transceiver. This chip has a 16 bit wide
DMA bus that I had connected directly with the outputs
from the A/D converter. It is the DMA (master MDMA
command 06) that drives the sampling.

The maximum sampling speed should be about 12 Msps.
 From what I measured on the pc, it is only sampling at
about 300Ksps. It is very frustrating: it is working, but not
at the sampling speed the chip shall be capable of.

Now I want to know if maybe I did something stupid and I
have conflicts on that bus, or I just forgot a setting. I tried
other timing settings there but the sampling rate is like a
stone, always 300 Ksps. And even with the highest timings,
there should be at least 2 Msps.

I put the schematic here
http://deep-blue.ro/tmp/main.pdf
I do not have another oscilloscope around so I can only
guess that the sampling is very low by measuring average
voltage on the CLK inputs of the converter. And that is
quite low about 0.5V when sampling is on, and 0V when off.

The subject is off topic, but I can link it with gEDA because
the hardware was made with gschem and pcb :)
http://deep-blue.ro/tmp/o2.html


Thanks,
Teodor



_______________________________________________
geda-user mailing list
geda-user@xxxxxxxxxxxxxx
http://www.seul.org/cgi-bin/mailman/listinfo/geda-user