LocalBus

LocalBus is a custom bus interface. You can use it for your register map, hovewer, it was designed specially to simplify integrating more common bus interfaces to register map. It acts as internal “virtual” interface.

In fact, all other supported buses (APB, AXI-Lite and etc.) in corsair are nothing more than just bridges to LocalBus interface under the hood.

Signals

Signal	Width	Direction	Description
waddr	>1	input	Write address bus
wdata	>1	input	Write data bus
wen	1	input	Write request enable signal
wstrb	>1	input	Write byte strobe bus (one bit for every write data byte)
wready	1	output	Write request ready signal
raddr	>1	input	Read address bus
ren	1	input	Read request enable signal
rdata	>1	output	Read data bus
rvalid	1	output	Read data valid signal

Note

Specific bit widths for buses are defined in globcfg section of a csrconfig file.

Transfers

Only simple single transfers are supported. No bursts or stream accesses. Every transfer can be extended with special signals.

Just for example, data bus is 32 bits wide for all the waveforms below.

Simple write

Write data D0 to address A0.

Write with bytes strobes

Byte strobe signalling to write only bytes 1 and 2 (wstrb = 0x6 = 0b0110) of D0 word.

Write with wait states

Write data D0 to address A0, then write D1 to A1 ends (wen goes low) as soon as wready become high.

Simple read

Read data D0 from address A0. Minimum response time - 1 tick. “Combinatoral” (in the same tick) read is not supported. Read ends (ren goes low) after rvalid is asserted.

Read with wait states

Read data D0 from address A0 with 2 wait states.