Shulou(Shulou.com)06/01 Report--

This article will explain in detail what are the most basic principles of writing ISR. The editor thinks it is very practical, so I share it with you for reference. I hope you can get something after reading this article.

The most basic principle of writing ISR is to be as short as possible. The lack of code is on the one hand, and more importantly, operations that may be blocked or delayed cannot be called in ISR.

Because ISR does not run in the context of regular tasks, and there is no TCB, all ISR share a stack (ISR_STACK_SIZE). Therefore, ISR cannot call functions that may block. For example, they cannot request a semaphore because the kernel tries to switch the applicant to a blocking state when the semaphore is not available; however, ISR can release the semaphore. In addition, the memory mechanisms malloc () and free () use semaphores, so these functions cannot be called in ISR, as well as any Create or Delete mechanisms. ISR is also unable to perform the Icano operation through the VxWorks driver. Although there are no fixed restrictions in the Icano system, most device drivers require task context because they may wait for feedback from the device. An important exception is VxWorks's plumbing mechanism (Pipe), where ISR can use Pipe for write operations. ISR can also call some of VxWorks's mechanisms to print messages to the system console: logMsg (), kprintf (), and kputs ().

ISR cannot invoke a mechanism that uses a floating point coprocessor. This is because in VxWorks, the interrupt driver code created by intConnect () does not save and recover floating-point registers. If ISR must use floating-point instructions, you need to use functions in fppArchLib to explicitly save and restore the registers of the floating-point coprocessor.

Be very careful when invoking C++ statements in ISR. The intConnect () mechanism requires the address of the function to be executed when an interrupt occurs, but the address of the non-static member function cannot be used, so the static member function must be implemented. And objects cannot be instantiated or deleted in ISR code. C++ code executed in ISR should be limited to embedded Clearing codes and should not use exception or RTTI (Run-Time Type Identification).

ISR should not directly access the shared data area (shared data region). ISR inherits the memory context of the task it preempts, and if the task does not map the shared data area, it cannot access the memory and causes an exception. In order to reliably access the shared data area, ISR can delegate the relevant operations to the task that maps the shared data area.

So what mechanisms or functions can be called in ISR?

BLib

All functions

ErrnoLib

ErrnoGet (), errnoSet ()

EventLib

EventSend ()

FppArchLib

FppSave (), fppRestore ()

IntLib

IntContext (), intCount (), intVecSet (), intVecGet ()

IntArchLib

IntLock (), intUnlock ()

LogLib

LogMsg ()

LstLib

All functions except lstFree ()

MathALib

When using fppSave () / fppRestore (), all functions

MsgQLib

MsgQSend ()

RngLib

All functions except rngCreate () / rngDelete ()

PipeDrv

Write ()

SelectLib

SelWakeup (), selWakeupAll ()

SemLib

SemFlush (), the semGive () of the non-mutex semaphore

SemPxLib

Sem_post ()

SigLib

Kill ()

TaskLib

TaskSuspend (), taskResume (), taskPrioritySet (), taskPriorityGet (), taskIdVerify (), taskIdDefault (), taskIsReady (), taskIsSuspended (), taskIsPended (), taskIsDelayed (), taskTcb ()

TickLib

TickAnnounce (), tickSet (), tickGet ()

TyLib

TyIRd (), tyITx ()

VxLib

VxTas (), vxMemProbe ()

WdLib

WdStart (), wdCancel ()

Communication mechanism that interrupts to the task

Shared memory. ISR can share variables, buffers, and ring buffers with task code

Semaphore. ISRs can release semaphores, and tasks can receive or wait for them (except mutexes and VxMP shared semaphores)

Message queue. ISR can send messages to message queues, except for shared message queues that use VxMP. If the queue is full, the message is discarded. MsgQSend (msgQId, buffer, nBytes, NO_WAIT,priority)

Pipes. ISR can send messages to the pipeline. If the pipe is full, discard the message

Signal. ISR can send signals to tasks, resulting in asynchronous scheduling of its signal handlers

VxWorks Event . ISR can send VxWorks Event to a task

This is the end of the article on "what are the most basic principles of writing ISR". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, please share it for more people to see.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.