at91rm3400 ATMEL Corporation, at91rm3400 Datasheet - Page 189

• Manufacturer Part Number: at91rm3400
• Description: Atmel Advanced At91 Arm Microcontroller
• Manufacturer: ATMEL Corporation

Debug
Communication
Channel Support
Chip Identifier
ICE Access
Prevention
1790A–ATARM–11/03
The Debug Unit handles the signals COMMRX and COMMTX that come from the Debug
Communication Channel of the ARM Processor and are driven by the In-circuit Emulator.
The Debug Communication Channel contains two registers that are accessible through the
ICE Breaker on the JTAG side and through the coprocessor 0 on the ARM Processor side.
As a reminder, the following instructions are used to read and write the Debug Communication
Channel:
Returns the debug communication data read register into Rd
Writes the value in Rd to the debug communication data write register.
The bits COMMRX and COMMTX, which indicate, respectively, that the read register has
been written by the debugger but not yet read by the processor, and that the write register has
been written by the processor and not yet read by the debugger, are wired on the two highest
bits of the status register DBGU_SR. These bits can generate an interrupt. This feature per-
mits handling under interrupt a debug link between a debug monitor running on the target
system and a debugger.
The Debug Unit features two chip identifier registers, DBGU_CIDR (Chip ID Register) and
DBGU_EXID (Extension ID). Both registers contain a hard-wired value that is read-only. The
first register contains the following fields:
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•
•
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•
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The second register is device-dependent and reads 0 if the bit EXT is 0.
The Debug Unit allows blockage of access to the system through the ARM processor's ICE
interface. This feature is implemented via the register Force NTRST (DBGU_FNR), that allows
assertion of the NTRST signal of the ICE Interface. Writing the bit FNTRST (Force NTRST) to
1 in this register prevents any activity on the TAP controller.
On standard devices, the bit FNTRST resets to 0 and thus does not prevent ICE access.
This feature is especially useful on custom ROM devices for customers who do not want their
on-chip code to be visible.
MRC
MCR
EXT - shows the use of the extension identifier register
NVPTYP and NVPSIZ - identifies the type of embedded non-volatile memory and its size
ARCH - identifies the set of embedded peripheral
SRAMSIZ - indicates the size of the embedded SRAM
EPROC - indicates the embedded ARM processor
VERSION - gives the revision of the silicon
p14, 0, Rd, c1, c0, 0
p14, 0, Rd, c1, c0, 0
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