Re: [Discuss-gnuradio] registers on FPGA

[Eric Blossom]

On Thu, Mar 23, 2006 at 11:17:14PM -0500, amit malani wrote:
> i hve 2 questions
> There some registers 32 of the which are common registers 64 to 79 are for
> custom use.
> what I understood all of them are written that is set from the host.  none
> of them is read from host. Is there any way by which I could communicate
> some message to host from FPGA.

There are a few registers that are read back from the host.
They're the ones's with names that start with FR_RB_* 
They're effectively in a different address space from the writable regs.


> If it is, then will the host need to pull the message..i mean keep polling
> or is it pushed from the USB controller may be by raising an interrupt.

I'm not sure if you know this, but reading or writing the FPGA
registers is a pretty slow operation.  Each one is a round trip across
the USB, and we bit-bang the register address and values from the FX2
to the FPGA.  [It worked for our purposes, but we weren't trying to do
real time control with them.]

> also,
> I wish to implement 2 buffers for one tx path on the FPGA. this could be
> done by putting multiplexer and demultiplexer across the buffers and select
> the needed one by setting the line select lines.
> Am thinking of doing this by configuring the user defined registers to do
> the line selects.

OK.

> my qestion is can we access those registers from time to time and set and
> reset them as and when needed? or is it just at the start only so that once
> they are set thats the final?
> am attaching a rough sketch of intended design.

You can set them whenever you like, as long as it makes sense to your
code in the FPGA.

Eric