EC Debug Service

The debug service is used for telemetry, debug logs, system reset information etc.

Recovery Mode

Put EC into recovery mode for development flashing and debugging.

Dump Debug State

EC should be able to support typical engineering requests, such as getting detailed subsystem information, setting/getting GPIOs, etc, for design verification and benchtop testing.

Telemetry

Ability to communicate with the HLOS event logging system, and record EC critical events for later analysis.

System Boot State

In many designs, OEMs will desire indication that the system is responding to a power on request. This could be a logo display on the screen or a bezel LED. EC should be able to control these devices during the boot sequence.

During first boot sequence EC may also be initialized and setup its services. Needs to know when OS is up to send notification for events that are only used by OS.

Memory Mapped Transactions

There are two cases where you may want to use the memory mapped transactions. The first is if you have a large buffer you need to transfer data between EC and HLOS like a debug buffer. The second use case is if you want to emulate an eSPI memory mapped interface for compatibility with legacy devices.

For this mode to work you will need memory carved out which is dedicated and shared between HLOS and secure world. In your UEFI memory map this memory should be marked as EfiMemoryReservedType so that the OS will not use or allocate the memory. In your SP manifest file you will also need to add access to this physical memory range. It needs to be aligned on a 4K boundary and a multiple of 4K. This memory region is carved out and must never be used for any other purpose. Since the memory is shared with HLOS there is also no security surrounding accesses to the memory.

Example Memory Mapped Interface

// Map 4K memory region shared
OperationRegion(ABCD, SystemMemory, 0xFFFF0000, 0x1000)

// DSM Method to send sync event
Method(_DSM,4,Serialized,0,UnknownObj, {BuffObj, IntObj,IntObj,PkgObj})
{
  // Compare passed in UUID to Supported UUID
  If(LEqual(Arg0,ToUUID(“6f8398c2-7ca4-11e4-ad36-631042b5008f”)))
  {
    // Use FFA to send Notification event down to copy data to EC
    If(LEqual(\\_SB.FFA0.AVAL,One)) {

      CreateQwordField(BUFF,0,STAT) // Out – Status for req/rsp
      CreateField(BUFF,128,128,UUID) // UUID of service
      CreateByteField(BUFF,32, CMDD) // In – First byte of command

      // Create Doorbell Event to read shared memory
      Store(0x0, CMDD) // 
      Store(ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), UUID) // Debug Service UUID
      Store(Store(BUFF, \_SB_.FFA0.FFAC), BUFF)

    } // End AVAL
  } // End UUID
} // End DSM

Any updates from the EC come back through a notification event registered in the FFA for this particular service.