SIO1007 datasheet(45/108 Pages) MICROCHIP

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DS00002020A-page 45

SIO1007

13.0

PCI CLKRUN SUPPORT

13.1

Overview

The SIO1007 supports the PCI nCLKRUN signal. nCLKRUN is used to indicate the PCI clock status as well as to

request that a stopped clock be started. See Figure 13-1 for an example of a typical system implementation using

nCLKRUN.

If the SIO1007 SIRQ_CLKRUN_EN signal is disabled, it will disable the nCLKRUN support related to LDRQ# in addition

to disabling the SER_IRQ and the nCLKRUN associated with SER_IRQ.

nCLKRUN is an open drain output and an input. Refer to the PCI Mobile Design Guide Rev 1.0 for a description of the

nCLKRUN function.

13.2

nCLKRUN for Serial IRQ

The SIO1007 supports the PCI CLKRUN# signal for the Serial IRQs. If an SIO interrupt occurs while the PCI clock is

stopped, nCLKRUN is asserted before the serial interrupt signal is driven active.

See Using nCLKRUN section below for more details.

13.3

nCLKRUN for LDRQ#

CLKRUN# support is also provided in the SIO1007 for the LDRQ# signal. If a device requests DMA service while the

PCI clock is stopped, CLKRUN# is asserted to restart the PCI clock. This is required to drive the LDRQ# signal active.

See Using nCLKRUN section for more details.

13.4

Using nCLKRUN

If nCLKRUN is sampled “high”, the PCI clock is stopped or stopping. If nCLKRUN is sampled “low”, the PCI clock is

starting or started (running). If a device in the SIO1007 asserts or de-asserts an interrupt or asserts a DMA request, and

nCLKRUN is sampled “high”, the SIO1007 requests the restoration of the clock by asserting the nCLKRUN signal asyn-

chronously (Table 13-1). The SIO1007 holds nCLKRUN low until it detects two rising edges of the clock. After the sec-

ond clock edge, the SIO1007 disables the open drain driver (Figure 13-2).

The SIO1007 will not assert nCLKRUN under any conditions if SIRQ_CLKRUN_EN is inactive (“0”). The SIRQ_-

CLKRUN_EN bit is D7 in CR29.

The SIO1007 will not assert nCLKRUN if it is already driven low by the central resource; i.e., the PCI CLOCK GENER-

ATOR in Figure 13-1. The SIO1007 will not assert nCLKRUN unless the line has been deasserted for two successive

clocks; i.e., before the clock was stopped (Figure 13-2).

Note 13-1

“Change/Assertion” means either-edge change on any internal IRQs routed to the SIRQ block or

assertion of an internal DMA request by a device in SIO1007. The “assertion” detection logic runs

asynchronously to the PCI Clock and regardless of the Serial IRQ mode; i.e., “continuous” or “quiet”.

Note 13-2

The nCLKRUN signal is ‘1’ for at least two consecutive clocks before SIO1007 asserts (‘0’) it.

TABLE 13-1:

SIO1007 NCLKRUN FUNCTION

SIRQ_CLKRUN_EN

Internal Interrupts/

DMA Requests

nCLKRUN

Action

None

NO CHANGE

None

CHANGE/ASSERTION (Note 13-

None

Assert nCLKRUN

(Note 13-2)

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