>> Another thing I wonder about, is if it's possible to have the CPU come online directly in protected mode or long mode after POWER_OK has settled and the motherboard releases the reset line.
> No. The BIOS needs to perform some touchy, hardware-specific initialization -- like detecting and calibrating RAM -- before releasing control to user code. It's not something you'd want the OS to be responsible for.
I think you misunderstood me. I didn't mention, and wasn't even thinking about the OS yet. As you said, UEFI handles the real->protected->long transitions. While the OS isn't loaded yet, and hardware initialization is being done, the CPU is still executing. What I'm talking about is setting the CPU's default power-on state, how it is before it begins executing even the boot firmware to initalize hardware and prepare to hand over execution to the OS.
By my understanding, when the power comes on, the motherboard waits for the PSU to assert POWER_OK. Once the PSU has done so, and POWER_OK has settled, then the mobo releases the CPU's RESET line, allowing the CPU to begin executing. At this point, the CPU is in real mode. What I am wondering is if the hardware can be configured so that once the motherboard releases RESET, the CPU is already in long mode, and begins executing the boot firmware. Is there something about the nature of pre-OS hardware initializtion that requires the CPU to be in real-mode to do this?
If CPUs could be coming online directly in long-mode, then perhaps the UEFI firmware could be simplified, since it doesn't need to handle the real->protected->long transitions anymore.
> No. The BIOS needs to perform some touchy, hardware-specific initialization -- like detecting and calibrating RAM -- before releasing control to user code. It's not something you'd want the OS to be responsible for.
I think you misunderstood me. I didn't mention, and wasn't even thinking about the OS yet. As you said, UEFI handles the real->protected->long transitions. While the OS isn't loaded yet, and hardware initialization is being done, the CPU is still executing. What I'm talking about is setting the CPU's default power-on state, how it is before it begins executing even the boot firmware to initalize hardware and prepare to hand over execution to the OS.
By my understanding, when the power comes on, the motherboard waits for the PSU to assert POWER_OK. Once the PSU has done so, and POWER_OK has settled, then the mobo releases the CPU's RESET line, allowing the CPU to begin executing. At this point, the CPU is in real mode. What I am wondering is if the hardware can be configured so that once the motherboard releases RESET, the CPU is already in long mode, and begins executing the boot firmware. Is there something about the nature of pre-OS hardware initializtion that requires the CPU to be in real-mode to do this?
If CPUs could be coming online directly in long-mode, then perhaps the UEFI firmware could be simplified, since it doesn't need to handle the real->protected->long transitions anymore.