Chapter 10 XGATE (S12XGATEV3)
MC9S12XE-Family Reference Manual , Rev. 1.19
372
Freescale Semiconductor
Section
for information on how to select priority levels for XGATE threads. Low priority threads (interrupt
levels 1 to 3) can be interrupted by high priority threads (interrupt levels 4 to 7). High priority threads are
not interruptible. The register content of an interrupted thread is maintained and restored by the XGATE
hardware.
To signal the completion of a task the XGATE is able to send interrupts to the S12X_CPU. Each XGATE
channel has its own interrupt vector. Refer to the
S12X_INT Section
for detailed information.
The XGATE module also provides a set of hardware semaphores which are necessary to ensure data
consistency whenever RAM locations or peripherals are shared with the S12X_CPU.
The following sections describe the components of the XGATE module in further detail.
10.4.1
XGATE RISC Core
The RISC core is a 16 bit processor with an instruction set that is well suited for data transfers, bit
manipulations, and simple arithmetic operations (see
Section 10.8, “Instruction Set”
).
It is able to access the MCU’s internal memories and peripherals without blocking these resources from
the S12X_CPU
1
. Whenever the S12X_CPU and the RISC core access the same resource, the RISC core
will be stalled until the resource becomes available again.
The XGATE offers a high access rate to the MCU’s internal RAM. Depending on the bus load, the RISC
core can perform up to two RAM accesses per S12X_CPU bus cycle.
Bus accesses to peripheral registers or flash are slower. A transfer rate of one bus access per S12X_CPU
cycle can not be exceeded.
The XGATE module is intended to execute short interrupt service routines that are triggered by peripheral
modules or by software.
10.4.2
Programmer’s Model
Figure 10-22. Programmer’s Model
1. With the exception of PRR registers (see Section “S12X_MMC”).
R7
R6
R5
R4
R3
R2
R1
R0 = 0
V C
Register Block
Program Counter
Condition
Code
Register
15
15
15
15
15
15
15
15
0
0
0
0
0
0
0
0
1 0
(Data Pointer)
PC
15
0
N Z
3 2
(Stack Pointer)
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
