ROM Cartridges Programming
All program code must be compiled to be relative of the
0x00FA0000 base address.
The
ULONG appearing at
0x00FA0000 determines the type of cartridge installed as follows:
| Cartridge Type |
ULONG Value |
| Application cartridge |
0xABCDEF42 |
| Diagnostic cartridge |
0xFA52255F |
Diagnostic Cartridges
Diagnostic cartridges are executed almost immediately after a system reset. The OS uses a 680x0
JMP instruction to begin execution at address
0x00FA0004 after having set the Interrupt Priority Level (IPL) to
7, entering supervisor mode, and executing a
RESET instruction to reset external hardware devices.
Upon execution, register
A6 will contain a return address which should be
JMP'd to if you wish to continue system initialization at any point. The stack pointers will contain garbage. In addition, keep in mind that no hardware has been initialized, particularly the memory controller. All system memory sizing and initialization must be performed by the diagnostic cartridge.
Application Cartridges
Application cartridges should contain one or more application headers beginning at location
0xFA0004 as follows (one cartridge may contain one or many applications):
| Name |
Offset |
Meaning |
| CA_NEXT |
0x00 |
Pointer to the next application header (or NULL if there are no more). |
| CA_INIT |
0x04 |
Pointer to the application's initialization code. The high 8 bits of this pointer have a special meaning as follows:
Bit Set: Meaning
0: Execute prior to display memory and interrupt vector initialization.
1: Execute just before GEMDOS is initialized.
2: (unused)
3: Execute prior to boot disk.
4: (unused)
5: Application is a Desk Accessory.
6: Application is not a GEM application.
7: Application needs parameters. |
| CA_RUN |
0x08 |
Pointer to application's main entry point. |
| CA_TIME |
0x0C |
Standard GEMDOS time stamp. |
| CA_DATE |
0x0E |
Standard GEMDOS date stamp. |
| CA_SIZE |
0x10 |
Size of application in bytes. |
| CA_NAME |
0x14 |
NULL terminated ASCII filename in standard GEMDOS 8+3 format. |
Executable files appear on the special
'c' drive as they would on any standard disk.