PCI Bridge
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor 9-33

Figure 9-20. Discard Timer Control register (PTCR)

Table9-7. describes PTCR fields.

9.11.1.7 General Purpose Control Register (GPCR)

The general purpose control register (GPCR), shown in Figure 9-21, contains control bits for rerouting

interrupts and adjusting the DMA controller’s 60x bandwidth.

31 30 24 23 16
Field EN PTV
Reset 0000_0000_0000_0000
R/W R/W
Addr 0x1087A
15 0
Field PTV
Reset 0000_0000_0000_0000
R/W R/W
Addr 0x10878

Table9-7. PTCR Field Descriptions

Bits Name Description
31 Enable Discard timer e nable.
0 Disable the discard timer
1 Enable the discard timer
30–24 — Reserved
23–0 Preload timer value Preload value for 24-bit discard timer. Delayed PCI read transactions to a
non-prefetchable address space remain valid within the PCI bridge a minimum of
(224 - Preload Timer Value) internal clock cycles. The discard timer is used to
discard delayed reads from non-prefetchable address space if the master has not
repeated the transaction in
n
internal clock cycles, where
n
= (224 - Preload Tim er
Value). Valid Preload Timer Values are in the range 0x000000–0xFFFFFE.
Example: To discard a delayed completion if the PCI master has not repeated the
transaction in 215 PCI clocks and the internal frequency is 2 to 1 to the PCI bus. The
Preload Timer Value should equal 224 -2
16 (0xFF0000).