SMC Networks AHB SRAM/NOR, PL241 manual Clock domain operation, Ahbc memory map

Functional Overview

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Figure 2-6 AHBC memory map

The other fourteen 4KB regions are read as zero. The lower 16 bits of the AHB address decode the memory controller that is being used. An external AHB decoder determines where in the system memory map, this 64KB region is located. See About the programmer’s model on page 3-2for information on the internal memory controller configuration registers. The configuration port of the internal memory controller is APB, so only word reads and writes are supported.

2.3.3Clock domain operation

The memory controller supports two clock domains:

•the AHB clock domain

•the static memory clock domain.

The hclk input drives the AHB clock domain. This clock drives the AHB interfaces and bus matrix. The static memory controller has a separate clock input in this domain. This is called smc_aclk. This signal is separated to enable the clock to be stopped independently of hclk for low-power operation, see Low-power interface operation on page 2-12.These two clocks must always be driven from the same clock source. The input signal hresetn resets this clock domain.

The static memory clock domain controls the memory interface logic of the SMC. The input signal smc_mclk0 and its inverse smc_mclk0n drive this domain. Each external static memory chip is driven by a gated smc_mclk0 signal, these are called smc_clk_out_0[3:0]. Clocks are only driven out to chips that require them. The static memory interface has a fed back clock input, smc_fbclk_in_0, to help with clock skews on the external pads.

The memory controller supports many different options for clocking the different domains:

ARM DDI 0389B Copyright © 2006 ARM Limited. All rights reserved. 2-11