5.1. About ARM922T clocking

The ARM922T processor has two functional clock inputs, BCLK and FCLK. Internally, the ARM922T is clocked by GCLK. This can be seen on the CPCLK output as shown in Figure 5.1. GCLK can be sourced from either BCLK or FCLK depending on the clocking mode, selected using nF bit and iA bit in CP15 register 1 (see Register 1, control register), and external memory access. The three clocking modes are:

The ARM922T processor is a static design and you can stop both clocks indefinitely without loss of state. Figure 5.1 shows that some of the ARM922T macrocell signals have timing specified with relation to GCLK. This can be either FCLK or BCLK depending on the clocking mode.

Figure 5.1. ARM922T clocking

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