LPC Peripheral Overview

This is an LPC peripheral that implements LPC IO and FW cycles so that it can boot a host like a POWER9. This peripheral would typically sit inside a BMC SoC.

It implements the Intel Low Pin Count (LPC) spec from here.

System diagram

                              .
                              .
  LPC       LPC Clock         .       System Clock
  pins                        .                        LPC FW               DMA
        +---------+     +------------+     +--------+ Wishbone +--------+ Wishbone
        |         |     |   ASYNC    |     |        |          |  LPC   |  Master
  LCLK  |         +---->|  FIFO WR   +---->|        +--------->|  CTRL  +-------->
------->|   LPC   |     |            |     |        |          |        |
        |  Front  |     +------------+     | LOGIC  |          +--------+
 LFRAME |         |           .            |        |
------->|         |     +------------+     |        |          +--------+
        |         |     |   ASYNC    |     |        |          | IPMI BT|
  LAD   |         |<----+  FIFO RD   |<----+        +--------->|  FIFO  |<--------
<------>|         |     |            |     |        |          |        |   IO
        +---------+     +------------+     +--------+  LPC IO  +--------+ Wishbone
                              .                       Wishbone |  UART  |  Slave
                              .                                |        |
                              .                                +--------+
                              .                                |  CTRL  |
                                                               |        |
                                                               +--------+

The design translates the LPC IO accesses into a wishbone master. The same is done for FW accesses.

The LPC IO wishbone master bus has devices attached to it. These include a an IPMI BT FIFO and standard 16550 UART. The back end of these can then be access by an external IO wishbone slave (which would typically come from the BMC CPU).

The LPC FW wishbone master gets translated into an external wishbone master. This translation provides an offset and mask so the external wishbone master accesses occur can be controlled. Typically this external wishbone will be hooked into a DMA path the system bus of the BMC, so where this can access needs to be controlled.

The LPC front end runs using the LPC clock. The rest of the design works on the normal system clock. Async FIFOs provide a safe boundary between the two.

HDL is written in nmigen because that's what all the cool kids are doing. This is our first nmigen project, and we are software developers, so be kind!

Building

This is designed to be integrated into some other project (like microwatt for libreBMC) not build as a standalone project.

If you want the verilog, do this to produce a lpcperipheral.v

python -m lpcperipheral.lpcperipheral

Testing

There are an extensive set of tests in tests/. To run these do:

python -m unittest