P912XDP512F0MPVR datasheet(205/1348 Pages) FREESCALE

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Chapter 6 XGATE (S12XGATEV2)

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

205

Figure 6-22 gives an example of the typical usage of the XGATE hardware semaphores.

Two concurrent threads are running on the system. One is running on the S12X_CPU and the other is

running on the RISC core. They both have a critical section of code that accesses the same system resource.

To guarantee that the system resource is only accessed by one thread at a time, the critical code sequence

must be embedded in a semaphore lock/release sequence as shown.

Figure 6-22. Algorithm for Locking and Releasing Semaphores

6.4.5

Software Error Detection

The XGATE module will immediately terminate program execution after detecting an error condition

caused by erratic application code. There are three error conditions:

•

Execution of an illegal opcode

•

Illegal vector or opcode fetches

•

Illegal load or store accesses

All opcodes which are not listed in section Section 6.8, “Instruction Set” are illegal opcodes. Illegal vector

and opcode fetches as well as illegal load and store accesses are deﬁned on chip level. Refer to the

S12X_MMC Section for a detailed information.

SSEM

XGSEM

≡ %1?

XGSEM

⇒ %0

BCC?

⇒ XGSEMx

CSEM

.........

critical

code

sequence

critical

code

sequence

S12X_CPU

XGATE

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