Technical information

59 Chapter 4
Bus Checkpoint Codes
The system BIOS pases control to different buses at the following checkpoints:
Additional Bus Checkpoints
While control is inside the different bus routines, additional checkpoints are output to I/O port address
0080h as word to identify the routines being executed.
These are word checkpoints. The low byte of checkpoint is the system BIOS checkpoint where
control is passed to the different bus routines.
The high byte of checkpoint indicates that the routine is being executed in different buses.
Checkpoint Code Description
2Ah Initializing the different bus system,static,and output devices, if present.
38h Initialized bus input, IPL, and general devices, if present.
39h Displaying bus initialization error messages, if any.
95h Initializing bus adaptor ROMs from C8000h through D8000h.
High Byte
Bits Description
Bits 7-4 0000 Function0. Disable all devices on the bus.
0001 Function1. Initialize static devices on the bus.
0010 Function2. Initialize output devices on the bus.
0011 Function3. Initialize input devices on the bus.
0100 Function4. Initialize IPL devices on the bus.
0101 Function 5. Initialize general devices on the bus.
0110 Function 6. Initialize error reporting on the bus.
0111 Function 7. Initialize add-on ROMs for all buses.
Bits 3-0 Specify the bus
0 Generic DIM Device Initialization Manager.
1 Onboard System devices.
2 ISA devices
3 EISA devices
4 ISA PnP devices
5. PCI devices