Intel 31154 Secondary IDSEL Masking, CompactPCI* Hot Swap Mode Select, Secondary Clock Control

PCI/PCI-X Interface

5.3.3Secondary IDSEL Masking

The 31154 supports private devices through the use of IDSEL masking. When the IDSEL_MASK pin is sampled as 1b on the trailing edge of P_RST#, the default value for the Secondary IDSEL Select Register (SISR) is 001Fh to mask devices 0–4 (refer to the Intel® 31154 133 MHz PCI Bridge Developer’s Manual for more information).

5.3.4Secondary Clock Control

The 31154 can disable its secondary clock outputs individually or globally. The straps S_CLKOEN[3:0] determine the number of S_CLKO[8:0] outputs that are enabled. The S_BRCLKO output is dedicated for the bridge feedback clock and cannot be individually disabled.

When the global clock output enable S_GCLKOEN is sampled as 0b, all secondary clock outputs are disabled, and an external clock source is required. The 31154 Bridge still drives the PCI-X initialization pattern, so any external clock source must be consistent with the clock generation scheme of the bridge, as defined in Table 9, “Secondary Bus Frequency Initialization” on page 33.

5.4CompactPCI* Hot Swap Mode Select

Hot Swap Mode Select (HS_SM) must be asserted (1b) to enable hot-swap functionality.

HS_FREQ[1:0] pins allow the bridge to determine the cPCI backplane operating frequency on its primary interface without needing to see a PCI-X initialization pattern. These pins are valid only when HS_SM is sampled as 1b during P_RST#.

Table 7.	HS_FREQ Encoding
	HS_FREQ[1:0]	P_M66EN	Operating Mode	Bus Frequency
	00	0	PCI	33 MHz
	00	1	PCI	66 MHz
	01	–	PCI-X	66 MHz
	10	–	PCI-X	100 MHz
	11	–	PCI-X	133 MHz

5.5Opaque Memory Region Enable

The 31154 supports an opaque memory region to enable private memory space for secondary devices. When OPAQUE_EN is sampled as 1b at the trailing edge of P_RST#, the Opaque Memory Enable bit in the “VCR2 Bridge Control Register 2” is set. The default base and limit reserve the upper half of memory (AD[63] = 1) for the private memory region.

Intel® 31154 133 MHz PCI Bridge Design Guide Design Guide 31