Chapter 10 XGATE (S12XGATEV3)
MC9S12XE-Family Reference Manual , Rev. 1.19
386
Freescale Semiconductor
10.8.4
Thread Execution
When the RISC core is triggered by an interrupt request (see
) it first executes a vector fetch
sequence which performs three bus accesses:
1. A
V
-cycle to fetch the initial content of the program counter.
2. A
V
-cycle to fetch the initial content of the data segment pointer (R1).
3. A
P
-cycle to load the initial opcode.
Afterwards a sequence of instructions (thread) is executed which is terminated by an "RTS" instruction. If
further interrupt requests are pending after a thread has been terminated, a new vector fetch will be
performed. Otherwise the RISC core will either resume a previous thread (beginning with a
P
-cycle to
refetch the interrupted opcode) or it will become idle until a new interrupt request is received. A thread can
only be interrupted by an interrupt request of higher priority.
10.8.5
Instruction Glossary
This section describes the XGATE instruction set in alphabetical order.
Table 10-23. Access Detail Notation
V
— Vector fetch: always an aligned word read, lasts for at least one RISC core cycle
P
— Program word fetch: always an aligned word read, lasts for at least one RISC core cycle
r
— 8 bit data read: lasts for at least one RISC core cycle
R
— 16 bit data read: lasts for at least one RISC core cycle
w
— 8 bit data write: lasts for at least one RISC core cycle
W
— 16 bit data write: lasts for at least one RISC core cycle
A
— Alignment cycle: no read or write, lasts for zero or one RISC core cycles
f
— Free cycle: no read or write, lasts for one RISC core cycles
Special Cases
PP/P
— Branch:
PP
if branch taken,
P
if not
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:
S12XE
products
in
208
MAPBGA
packages