System information

5.3 Computer Power Control
0x410
0x414
0x418
0x41C
0x420
0x424
0x41E
{
1 Byte
ASCII
Scancode
0x43D
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
0
15
Start
Pointer
1 Byte
End
Pointer
Figure 5.9: Organization of the keyboard buffer of the BIOS.
can contain 16 characters. The BIOS keyboard buffer can be used to emulate keystrokes.
This technique is referred to as stuff keys by programmers. The emulated keystrokes are
written into the keyboard buffer behind the tail of the buffer. Afterwards, the end pointer
of the buffer is appropriately changed. The next call of the BIOS keyboard handler provides
the emulated keystrokes to the calling program. The BIOS recognizes the change of the
end pointer and reads out the keycodes. However, the use of the BIOS keyboard to emulate
keystrokes is restricted to the run of the computer BIOS Setup Utility and the boot up of
the computer. The operating system uses their own keyboard buffer to handle keystrokes
and the BIOS keyboard buffer is not used by the running operating system.
5.3 Computer Power Control
Sometimes a computer has to be rebooted or powered down. The CHARM has an interface
to hook the power and the reset switch of the motherboard. The CHARM shares both, the
power and the reset switch, with the computer chassis. The computer can be switched on
either with the power button of the chassis or by the CHARM card by remote control. But
the CHARM has to be powered by a standby power source in this process. Otherwise, the
CHARM will be switched off while powering down the computer.
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