st20-gp6 STMicroelectronics, st20-gp6 Datasheet - Page 80

• Manufacturer Part Number: st20-gp6
• Description: Gps Processor
• Manufacturer: STMicroelectronics

ST20-GP6
:
14.5 Peeking and poking the host from the target
The target CPU can peek and poke the host via the diagnostic controller. This is done by reading or
writing a single word to a block of addresses within the DCU register block. The DCU will then send
a peek or poke message to the host. After a host peek , the target CPU will wait until the host
responds with a peeked message, which the DCU returns to the CPU as memory read data.
Peeking and poking the host from the target can be enabled or disabled. After reset, these bits are
cleared, so peek and poke from the target are disabled.
14.6 Abortable instructions
14.6.1 Properties of the hardware implementation
In the ST20-C2 core, some instructions are abortable, i.e. they may be “started” more than once. In
the instruction set chapter, abortable instructions are marked with an ‘A’ in the notes column, indi-
cating that the instruction can be aborted and later restarted.
The breakpoint mechanism in the DCU, follows the CPU behavior, and takes a trap in place of
starting an instruction with an Iptr which matches. Care is taken in the hardware to ensure that any
interrupts which might have occurred following the preceding instruction are allowed in, and the
trap is taken only if the CPU was about to start the instruction with an Iptr which matches.
If the DCU is programmed to break on an instruction, then normally, following the trap return
instruction, that instruction is executed. In this scenario, all instructions should be considered as
abortable. If an interrupt occurs between the end of the trap handler and the start of the instruction,
then when the interrupt completes the DCU will again trap on that instruction (if the breakpoint is
repeatable).
The user needs to be aware that setting a breakpoint on a given instruction may break more than
once on the same instruction in the same thread.
80/123
Command messages
Poke
Peek
Response messages
Peeked
Triggered
Header
Header
Header
Header
First data word
Address
Address
Figure 14.2 Message formats
First data word
Second data word
Third data word
Second data word