SMC Networks AHB SRAM/NOR AHB domain, Memory clock domain, Synchronous clocking, Output clocks

Functional Overview

These clocks can be grouped into two clock domains:

AHB domain	smc_aclk is in this domain. You can only stop the smc_aclk
	domain signals when the SMC is in low-power mode.

Memory clock domain

The smc_mclk0 and smc_mclk0n are in this domain.

smc_mclk0n is an inverted version of smc_mclk0. smc_mclk0 is used for timing and control signals.

You can tie off the smc_async and smc_msync pins so that the smc_aclk and

smc_mclk0 clock domains can operate synchronously or asynchronously with respect to each other.

Synchronous clocking

The benefit of synchronous clocking is that you can reduce the read and write latency by removing the synchronization registers between clock domains. However, because of the integer relationship of the clocks, you might not be able to get the maximum performance from the system because of constraints placed on the bus frequency by the external memory clock speed. In synchronous mode, the handshaking between the smc_aclk and smc_mclk0 domains enables synchronous operation of the two clocks at multiples of each other, that is, ratios of n:1 and 1:m.

Asynchronous clocking

The main benefit of asynchronous clocking is that you can maximize the system performance, while running the memory interface at a fixed system frequency. Additionally, in sleep-mode situations when the system is not required to do much work, you can lower the frequency to reduce power consumption.

Output clocks

A clock output is provided for every external memory device on the SRAM memory interface type.

Resets

The SMC has two reset inputs:

hresetn This is the reset signal for the smc_aclk domain.

smc_mreset0n

This is the reset signal for the smc_mclk0 domain.

ARM DDI 0389B Copyright © 2006 ARM Limited. All rights reserved. 2-17