PCH Direct eSPI VW Channel Support

The PCH Direct eSPI target supports Virtual Wire channel in both transmit and receive directions. It receives VWs from the internal eSPI switch or from the processor Direct eSPI controller.

The processor Direct eSPI enables the VW channel after ESPI_​RESET# has been de-asserted and the eSPI link has been initialized and configured. The VW channel is automatically disabled upon ESPI_​RESET# assertion.

The PCH Direct eSPI target must not send any VW (except Device_​Boot_​Load_​done/status) until the processor Direct eSPI controller has sent its first set of VWs to the PCH. Otherwise, this might lead to unexpected system behavior due to mismatched VW states between the PCH and the processor.

The PCH eSPI target does not generate VW cycles internally. All VWs including device_​boot_​load_​done/status VW from/to EC are forwarded from/to eSPI switch and sent to/from the processor Direct eSPI controller.

The PCH Direct eSPI target resets VW states based on the eSPI base specification. After sending the HOST_​RST_​ACK, the PCH Direct eSPI target does not send any host domain VWs such as SMI#, SCI#, RCIN#, or IRQ. Until PLTRST# is de-asserted, host domain VWs are not sent from the Direct eSPI controller or target.

The PCH Direct eSPI target accepts the VW packets at any time as long as the channel is enabled.