Re: [Discuss-gnuradio] Auxiliary ADC

[Doug Geiger]

Eric Blossom wrote:
> On Wed, Jan 20, 2010 at 07:20:43PM +0100, Christoph Thein wrote:
>   
> > > On 01/19/2010 10:35 AM, Christoph Thein wrote:
> > >       
> > > > > On 01/19/2010 09:47 AM, Christoph Thein wrote:
> > > > >           
> > > > > > Hi,
> > > > > >
> > > > > > is there a possibility to read the data coming from the auxiliary ADC
> > > > > > (AD7922) at the moment?  I couldn't find any hint in the code or on the
> > > > > > mailing list that could point me to a good direction to start.
> > > > > >
> > > > > > Just out of interest: What should the auxiliary DAC (AD5623) be used
> > > > > > for?
> > > > > >             
> > The USRP1 uses the read_aux_adc function to get the values. Does the read_gpio 
> > replace it for the USRP2? If not how is the USRP2 accessing the aux ADC?
> >
> > Cheers,
> > Christoph
> >     
>
> At this point, firmware in the USRP2 controls the daughterboards, and
> the read_aux_adc functionality is not exported to the host.
>
> Eric
>
>
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>   
Does the firmware currently do anything with the Aux ADC? I see the 
definitions for reading from the SPI controller, and the function 
(firmware/lib/lsadc.c: lsadc_read_rx(int)) which appears to be the only 
place that reads from the correct SPI device. Also, it looks like it 
would be difficult to read the value directly from inside the FPGA: i.e. 
if I wanted to use the RSSI value for an AGC or squelch control, I'd 
probably be best served by periodically reading the value from within 
the firmware, and pushing it back into a register in, e.g., dsp_rx_regs. 
This would likely mean I'd have some additional inherent delay in using 
the value in the DSP chain. Is there a better way - e.g. I assume it 
would be possible to load the data from the SPI controller in the FPGA, 
but does that come with a (much?) larger cost in terms of logic, and 
therefore area/etc.?
Thanks,
 Doug

--
Douglas Geiger
Code 5545
U.S. Naval Research Laboratory
Washington, DC 20375
(202) 767-9048
address@hidden