
GR716-DS-UM, May 2019, Version 1.29
147
www.cobham.com/gaisler
GR716
19
Hardware Debug Support Unit
19.1
Overview
To simplify debugging on target hardware, the LEON3 processor implements a debug mode during
which the pipeline is idle and the processor is controlled through a special debug interface. The
LEON3 Debug Support Unit (DSU) is used to control the processor during debug mode. The DSU
acts as an AHB slave and can be accessed by any AHB master. An external debug host can therefore
access the DSU through several different interfaces.
19.2
Operation
Through the DSU AHB slave interface, any AHB master can access the processor registers and the
contents of the instruction trace buffer. The DSU control registers can be accessed at any time, while
the processor registers and trace buffer can only be accessed when the processor has entered debug
mode. In debug mode, the processor pipeline is held and the processor state can be accessed by the
DSU. Entering the debug mode can occur on the following events:
•
executing a breakpoint instruction (ta 1)
•
integer unit hardware breakpoint/watchpoint hit (trap 0xb)
•
rising edge of the external break signal (DSUBRE)
•
setting the break-now (BN) bit in the DSU control register
•
a trap that would cause the processor to enter error mode
•
occurrence of any, or a selection of traps as defined in the DSU control register
•
after a single-step operation
•
the processor has entered the debug mode
•
DSU AHB breakpoint or watchpoint hit
Processor
LEON3FT
Unit
AMBA AHB BUS
Debug Support
AHB Slave I/F
Debug I/F
AHB Master I/F
Figure 15.
LEON3FT/DSU Connection
I2C2AHB
DEBUG HOST
SPI2AHB
SpaceWire
Debug UART
UART