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Re: [Discuss-gnuradio] CORDIC in USRP TX path

From: Christian Meier
Subject: Re: [Discuss-gnuradio] CORDIC in USRP TX path
Date: Thu, 08 Oct 2009 18:39:24 +0100
User-agent: Thunderbird (Windows/20090812)

Matt Ettus wrote:
Christian Meier wrote:
I noticed that there is a hardcoded "`define NOCORDIC_TX" inside tx_chain.v

Does anyone know why this is disabled?
Is it a problem of FPGA size or are there any bugs inside tx_chain with NOCORDIC_TX not defined?

Ignore my last answer. We use the RX cordic. The TX cordic is not used because there is the equivalent functionality in the AD9862 DAC, so we don't need to include it in the FPGA, and thus can save space.

Hi once more,
I am currently writing a patch that reactivates the disabled and out of date integration of the tx cordic inside FPGA. If this works and fits into the FPGA, I plan to use it for getting more tx and rx channels over the same daugtherboard with different baseband offsets. For this to work the tx and rx pipelines of a 2rx + 2tx configuration have to be combined after tx_chain / before rx_chain.
This is done in a tx_combiner module.

Find attached the current progress as a patch. [Update: posting did not work with attached file ;(] I haven't neither tested nor synthesized it yet at all. I just wanted to give a base for discussion.
If someone has any comments or further ideas on that, please let me know.

By the way, what is the firmware/fpga_regs0.h file good for? I didn't find any file that uses these defines, or any .v file that includes fpga_regs0.v. For the patch to compile we also need some new register definitions of FR_TX_(FREQ|PHASE)_[01] and FR_TX_COMBINER.

What do you think of this idea?


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