
EP7309/11/12 User’s Manual - DS508UM4 2-7
Copyright Cirrus Logic, Inc. 2003
CPU Core
22
2
Debug Interface
JTAG (Joint Test Action Group) or IEEE 1149 provides a boundary scan test interface
with 5 dedicated signals connected directory to the CPU core:
•TRST-TestReset(activelow)
•TCK-TestClock
• TMS - Test Mode Select
•TDI-TestDataIn
•TDO-TestDataOut
See Chapter 14for moreinformationon debugging the EP73xx viathe JTAG interface.
CPU Register Definitions
ARM has 3732-bit internal registers. If operatingin Thumb mode, the processor must
switch to ARM mode before taking an exception.The return instruction will restore
the processor to Thumb state. Most tasks are executed out of User mode.
User: Unprivileged normal operating mode.
FIQ: Fast interrupt (high priority) mode when FIQ is asserted
IRQ: Interrupt request (normal) mode when IRQ is asserted
Supervisor: Software interrupt instruction (SWI) or reset will cause entry into
this mode
Abort: Memory access violation will cause entry into this mode
Undef: Undefined instructions
System: Privileged mode. Uses same registers as user mode
Figure 2-3 on page 2-8 illustrates the use of all registers for the following core
operating modes. Each will bank or store a specific number of registers. Banked
register information is not shared between modes. FIQs bank the fewest number of
registers which increases performance.
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