Atmel ARM-Based Evaluation Kit AT91SAM9N12-EK AT91SAM9N12-EK Data Sheet

267

SAM9N12/SAM9CN11/SAM9CN12 [DATASHEET]

11063K–ATARM–05-Nov-13

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:

MRC

p14, 0, Rd, c1, c0, 0

Returns the debug communication data read register into Rd

MCR

p14, 0, Rd, c1, c0, 0

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 permits handling under interrupt a debug link between a debug monitor running on the target system and a
debugger.

Receiver

Transmitter

Disabled

RXD

TXD

Receiver

Transmitter

Disabled

RXD

TXD

V

DD

Disabled

Receiver

Transmitter

Disabled

RXD

TXD

Disabled

Automatic Echo

Local Loopback

Remote Loopback

V

DD