Chapter 9 Interrupt Controller (INTC)
MPC5602P Microcontroller Reference Manual, Rev. 4
Freescale Semiconductor
227
acknowledge. The ISR, however, can have a portion that does not need to be executed at this higher
priority. Therefore, executing the later portion that does not need to be executed at this higher priority can
prevent the execution of ISRs that do not have a higher priority than the earlier portion of the ISR but do
have a higher priority than what the later portion of the ISR needs. This preemptive scheduling inefficiency
reduces the processor’s ability to meet its deadlines.
One option is for the ISR to complete the earlier higher priority portion, but then schedule through the
RTOS a task to execute the later lower priority portion. However, some RTOSs can require a large amount
of time for an ISR to schedule a task. Therefore, a second option is for the ISR, after completing the higher
priority portion, to set a SET
x
bit in INTC_SSCIR0_3–INTC_SSCIR4_7. Writing a ‘1’ to SET
x
causes a
software configurable interrupt request. This software configurable interrupt request will usually have a
lower PRI
x
value in the INTC_PSR
x
_
x
and will not cause preemptive scheduling inefficiencies. After
generating a software settable interrupt request, the higher priority ISR completes. The lower priority ISR
is scheduled according to its priority. Execution of the higher priority ISR is not resumed after the
completion of the lower priority ISR.
9.7.7.2
Scheduling an ISR on another processor
Because the SET
x
bits in the INTC_SSCIR
x
_
x
are memory mapped, processors in multiple-processor
systems can schedule ISRs on the other processors. One application is that one processor wants to
command another processor to perform a piece of work and the initiating processor does not need to use
the results of that work. If the initiating processor is concerned that the processor executing the software
configurable ISR has not completed the work before asking it to again execute the ISR, it can check if the
corresponding CLR
x
bit in INTC_SSCIR
x
_
x
is asserted before again writing a ‘1’ to the SET
x
bit.
Another application is the sharing of a block of data. For example, a first processor has completed
accessing a block of data and wants a second processor to then access it. Furthermore, after the second
processor has completed accessing the block of data, the first processor again wants to access it. The
accesses to the block of data must be done coherently. To do this, the first processor writes a ‘1’ to a SET
x
bit on the second processor. After accessing the block of data, the second processor clears the
corresponding CLR
x
bit and then writes 1 to a SET
x
bit on the first processor, informing it that it can now
access the block of data.
9.7.8
Lowering priority within an ISR
A common method for avoiding preemptive scheduling inefficiencies with an ISR whose work spans
multiple priorities (see
Section 9.7.7.1, “Scheduling a lower priority portion of an ISR
) is to lower the
current priority. However, the INTC has a LIFO whose depth is determined by the number of priorities.
NOTE
Lowering the PRI value in INTC_CPR within an ISR to below the ISR’s
corresponding PRI value in INTC Priority Select Registers
(INTC_PSR0_3–INTC_PSR220_221) allows more preemptions than the
LIFO depth can support.
Therefore, the INTC does not support lowering the current priority within an ISR as a way to avoid
preemptive scheduling inefficiencies.
Содержание SAFE ASSURE Qorivva MPC5601P
Страница 2: ...MPC5602P Microcontroller Reference Manual Rev 4 2 Freescale Semiconductor ...
Страница 4: ...MPC5602P Microcontroller Reference Manual Rev 4 4 Freescale Semiconductor ...
Страница 62: ...Chapter 2 MPC5602P Memory Map MPC5602P Microcontroller Reference Manual Rev 4 62 Freescale Semiconductor ...
Страница 104: ...Chapter 4 Clock Description MPC5602P Microcontroller Reference Manual Rev 4 104 Freescale Semiconductor ...
Страница 128: ...Chapter 6 Power Control Unit MC_PCU MPC5602P Microcontroller Reference Manual Rev 4 128 Freescale Semiconductor ...
Страница 272: ...Chapter 12 e200z0 and e200z0h Core MPC5602P Microcontroller Reference Manual Rev 4 272 Freescale Semiconductor ...
Страница 280: ...Chapter 14 Crossbar Switch XBAR MPC5602P Microcontroller Reference Manual Rev 4 280 Freescale Semiconductor ...
Страница 306: ...Chapter 16 Internal Static RAM SRAM MPC5602P Microcontroller Reference Manual Rev 4 306 Freescale Semiconductor ...
Страница 380: ...Chapter 17 Flash Memory MPC5602P Microcontroller Reference Manual Rev 4 380 Freescale Semiconductor ...
Страница 532: ...Chapter 21 LIN Controller LINFlex MPC5602P Microcontroller Reference Manual Rev 4 532 Freescale Semiconductor ...
Страница 578: ...Chapter 22 FlexCAN MPC5602P Microcontroller Reference Manual Rev 4 578 Freescale Semiconductor ...
Страница 708: ...Chapter 25 FlexPWM MPC5602P Microcontroller Reference Manual Rev 4 708 Freescale Semiconductor ...
Страница 742: ...Chapter 26 eTimer MPC5602P Microcontroller Reference Manual Rev 4 742 Freescale Semiconductor ...
Страница 760: ...Chapter 27 Functional Safety MPC5602P Microcontroller Reference Manual Rev 4 760 Freescale Semiconductor ...
Страница 782: ...Chapter 28 Fault Collection Unit FCU MPC5602P Microcontroller Reference Manual Rev 4 782 Freescale Semiconductor ...
Страница 788: ...Chapter 29 Wakeup Unit WKPU MPC5602P Microcontroller Reference Manual Rev 4 788 Freescale Semiconductor ...
Страница 798: ...Chapter 30 Periodic Interrupt Timer PIT MPC5602P Microcontroller Reference Manual Rev 4 798 Freescale Semiconductor ...
Страница 816: ...Chapter 32 Cyclic Redundancy Check CRC MPC5602P Microcontroller Reference Manual Rev 4 816 Freescale Semiconductor ...
Страница 848: ...Chapter 33 Boot Assist Module BAM MPC5602P Microcontroller Reference Manual Rev 4 848 Freescale Semiconductor ...
Страница 930: ...Chapter 36 Nexus Development Interface NDI MPC5602P Microcontroller Reference Manual Rev 4 930 Freescale Semiconductor ...