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Re: [Discuss-gnuradio] USRP2 Filtering/Decimation Question
From: |
Eric Blossom |
Subject: |
Re: [Discuss-gnuradio] USRP2 Filtering/Decimation Question |
Date: |
Fri, 4 Sep 2009 14:56:59 -0700 |
User-agent: |
Mutt/1.5.18 (2008-05-17) |
On Fri, Sep 04, 2009 at 05:01:59PM -0400, Bruce McGuffin wrote:
> Matt Ettus wrote:
>> Bruce McGuffin wrote:
>>
>>> Hi
>>>
>>> When I specify a particular receiver decimation rate
>>> for the USRP2, the task of decimating is presumably
>>> split up between the CIC and two half-band filters.
>>> My question is how is the task split up,
>>> and where in the code does this happen?
>>>
>>
>> If the requested decimation rate is a multiple of four, we use the two
>> halfband filters, and the rest is CIC. If it is only a multiple of
>> two, we use one halfband filter and the rest in CIC. If it is an odd
>> number, we use only CIC.
>>
>> Matt
>>
> When the decimation rate is divisible by 2 but not 4, which half-band
> filter do you use?
> And where in the code is this decision made?
>
> Bruce
Hi Bruce!
The decision is made in the firmware. See
usrp2/firmware/apps/app_common_v2.c line 247, in the function
config_rx_v2_cmd.
The actual control register (dsp_rx_regs->decim_rate) is written on line 265.
Eric