IBM 560 - Manual (Page 70)

Calling Convention
The client can invoke the SMAPI BIOS with a far-call to the entry
point that is specified in the header file. All parameters for the BIOS
and other results are stored in the client data area; the client needs
to prepare an input parameter / output parameter area in its data
area, and informs this area by pushing those pointers onto the its
stack before the far-calls.
The SMAPI BIOS uses the stack/data area directly with the selector
when the BIOS is invoked. Therefore, the caller needs to define the
same privilege level as the BIOS.
Parameter Structure
The memory allocation for the input/output field should be prepared
by the caller. The input field specifies the function request to the
SMAPI BIOS, and the BIOS fills in the return value to the output
field.
Input Field
Field Offset Length
Major Function Number 00h Byte
Minor Function Number 01h Byte
Parameter 1 02h Word
Parameter 2 04h Word
Parameter 3 06h Word
Parameter 4 08h Dword
Parameter 5 0Ch Dword
Output Field
Field Offset Length
Return Code 00h Byte
Auxiliary Return Code 01h Byte
Parameter 1 02h Word
Parameter 2 04h Word
Parameter 3 06h Word
Parameter 4 08h Dword
Parameter 5 0Ch Dword
A-6 ThinkPad 560/560E SMAPI BIOS