Functional Description
ARM DDI 0363G Copyright © 2006-2011 ARM Limited. All rights reserved. 2-12
ID073015 Non-Confidential
Whenever nSYSPORESET is asserted, nRESET must also be asserted. The processor will not
be correctly reset otherwise.
This section of the manual describes:
• Power-on reset
• Processor reset
• Normal operation
• Halt operation.
Power-on reset
You must apply power-on or cold reset to the processor when power is first applied to the
system. In the case of power-on reset, the leading, or falling, edge of the reset signals, nRESET
and nSYSPORESET, does not have to be synchronous to CLKIN. Because the nRESET and
nSYSPORESET signals are synchronized within the processor, you do not have to synchronize
these signals. Figure 2-2 shows the application of power-on reset.
Figure 2-2 Power-on reset
ARM recommends that you assert the nRESET signal for at least four CLKIN cycles to ensure
correct reset behavior.
It is not necessary to assert PRESETDBGn on power-up.
Processor reset
A processor or warm reset initializes the majority of the processor, excluding the CoreSight
logic. Processor reset is typically used for resetting a system that is operating for some time, for
example, watchdog reset.
Because the nRESET signal is synchronized within the processor, you do not have to
synchronize this signal. ARM recommends that you assert the nReset signal for at least four
CLKIN cycles to ensure correct reset behavior.
Normal operation
During normal operation, neither processor reset nor power-on reset is asserted. If CoreSight
logic is not used, the value of PRESETDBGn does not matter.
Halt operation
When nCPUHALT is asserted, and nSYSPORESET and nRESET deasserted, the processor
is out of reset, but the PFU is inhibited from fetching instructions. For example, you can use
nCPUHALT to enable DMA into the TCMs using the processor. You can then deassert
nCPUHALT and the PFU starts fetching instructions from TCMs. When the processor has
started fetching, nCPUHALT must not be asserted again except when the processor is reset.
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