6. Arbitration
140
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
Figure 21: Arbitration Algorithm
Each PowerSpan II PCI arbiter is programmable with the corresponding arbiter control register (see
“PCI-1 Bus Arbiter Control Register” on page 284
) and enabled through power-up option PCI x
Arbiter enable (PWRUP_Px_ARB_EN) (see
“Resets, Clocks and Power-up Options” on page 167
).
Each master has a arbitration level for PCI Master Device x (Mx_PRI) bit in the
(Px_ARB_CTRL) to determine its arbitration level.
External Arbitration
When an external arbiter is used, the PowerSpan II PCI Master uses Px_REQ#[1]/Px_GNT#[1] to
acquire the bus.
Master X
Master Y
Master Z
Level 0
Master C
Level 0
Master A
Master B
Level 1
Arbitration Order
Level 1, Level 1, Level 1, Level 0
For example, if all bus masters
assert Request:
* A, B, C, X
* A, B, C, Y
* A, B, C, Z
* A, B, C, X