The address range for a GIO bus device is determined in part by the slot number of the device. The hardware must be designed to determine which slot the device is in and make the appropriate adjustments to respond to that slot's address range.
Indigo and Indy systems provide two GIO address spaces known as exp0 and exp1. Indigo2 systems also have two slots, but support three GIO address spaces, referred to as gfx, exp0, and exp1. The gfx address space is used by the graphics card.
Table 18-1 shows the slot names and address spaces available on the Indigo, Indigo2, and Indy platforms.
| Slot Name | Address | Indigo/Indy | Indigo2 |
|---|---|---|---|
| gfx | 0x1f00 0000-0x1f3f ffff | N/A | Available |
| exp0 | 0x1f40 0000-0x1f5f ffff | Available | Available |
| exp1 | 0x1f60 0000-0x1f9f ffff | Available | Available |
In 64-bit systems (Indigo2 Maximum Impact), two additional high-order bits are needed to select the physical address of the GIO space, so each of the above addresses is prefixed by 0x9000 0000. The 64-bit gfx space, for example, is at 0x9000 0000 1f00 0000.
GIO-bus devices use only one interrupt level -- interrupt 1. Interrupts 0 and 2 are used by the graphics system and may not be used by GIO-bus devices.