[USRP-users] Addressing custom logic in fpga

Johnathan Corgan johnathan at corganlabs.com
Wed Feb 13 08:57:56 EST 2013

On Tue, Feb 12, 2013 at 10:40 PM, Ian Buckley <ianb at ionconcepts.com> wrote:

> If you do ever add further logic to the Verilog and find you are running
> short off address space, then it is quite simple to add a new settings_bus
> bridge, identical to the existing one to one of the unused Wishbone bus
> slave locations so that you have an entire new settings bus to use.

There is already a dedicated settings bus in place specifically for use in
custom designs, which allows the user to create up to 256 32-bit write-only
configuration registers that exist outside the address space of the
standard settings bus.

In the top level module (e.g., u2plus_core.v), there are wires
'set_addr_user', 'set_data_user', and 'set_stb_user', with the same
semantics as the standard configuration bus.  To use these in a custom
design, one creates new instances of 'settings_reg' but connects their
inputs to this set of wires instead.

To initiate a write cycle, from the host UHD interface one issues a call to:

 void set_user_register(const boost::uint8_t addr, const boost::uint32_t
data, size_t mboard = ALL_MBOARDS)

...from an instance of uhd::usrp::multi_usrp.  This call is also part of
the GNU Radio UHD source and sink blocks.

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