Overview of Reentrant Functions, IPC, and Priority Management in Embedded Systems & IoT

Overview of Reentrant Functions, IPC, and Priority Management in Embedded Systems & IoT

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  RAJASEKAR T, AP/ECE 20EC211-Embedded Systems & IoT 1
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  RAJASEKAR T, AP/ECE ReentrantFunctions • A reentrant function can be used by more than one task without fear of data corruption. • A re-entrant function can be interrupted at any time and resumed at a later time without loss of data. • Reentrant functions either use local variables (i.e., CPU registers or variables on the stack) or protect data when global variables are used. 20EC211- Embedded Systems & IoT 2
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  RAJASEKAR T, AP/ECE ReentrantFunctions • Copies of the arguments to strcpy() are placed on the task’s stack, strcpy() can be invoked by multiple tasks without fear that the tasks will corrupt each other’s pointers. 20EC211- Embedded Systems & IoT 3
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  RAJASEKAR T, AP/ECE Non-ReentrantFunctions 20EC211- Embedded Systems & IoT 4
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  Rajasekar T AP/ECE5 Shared resources • Critical sections • Semaphores • The semaphore is used to guard a resource. • The semaphore names are, by tradition, P() to gain access to the protected resource and V() to release it. • /* some nonprotected operations here */ • P(); /* wait for semaphore */ • /* do protected work here */ • V(); /* release semaphore */ 20EC211- Embedded Systems & IoT
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  RAJASEKAR T, AP/ECE 20EC211-Embedded Systems & IoT 6
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  Rajasekar T AP/ECE9 Priority inversion • Shared resources cause a new and subtle scheduling problem: a low- priority process blocks execution of a higher-priority process by keeping hold of its resource, a phenomenon known as priority inversion. 20EC211- Embedded Systems & IoT
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  Rajasekar T AP/ECE11 Priority inheritance • The most common method for dealing with priority inversion is priority inheritance: promote the priority of any process when it requests a resource from the operating system. • The priority of the process temporarily becomes higher than that of any other process that may use the resource. • Once the process is finished with the resource, its priority is demoted to its normal value. 20EC211- Embedded Systems & IoT
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  Rajasekar T AP/ECE32 Inter process communication mechanisms • There are two major styles of inter process communication: • Shared memory • Message passing. 20EC211- Embedded Systems & IoT
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  Rajasekar T AP/ECE33 Shared memory communication 20EC211- Embedded Systems & IoT
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  Rajasekar T AP/ECE34 • Two components, such as a CPU and an I/O device, communicate through a shared memory location. 20EC211- Embedded Systems & IoT
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  Rajasekar T AP/ECE35 Elastic Buffers as Shared Memory • The text compressor uses the CPU to compress incoming text, which is then sent on a serial line by a UART. 20EC211- Embedded Systems & IoT
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  Rajasekar T AP/ECE36 20EC211- Embedded Systems & IoT
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  Rajasekar T AP/ECE37 Message passing 20EC211- Embedded Systems & IoT
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  Rajasekar T AP/ECE38 • The message is not stored on the communications link, but rather at the senders/receivers at the endpoints. • In contrast, shared memory communication can be seen as a memory block used as a communication device, in which all the data are stored in the communication link/memory. 20EC211- Embedded Systems & IoT
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  Rajasekar T AP/ECE53 Queue • A queue is a common form of message passing. The queue uses a FIFO discipline and holds records that represent messages. 20EC211- Embedded Systems & IoT
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  Rajasekar T AP/ECE54 20EC211- Embedded Systems & IoT
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  Rajasekar T AP/ECE55 Signals • A signal is simple because it does not pass data beyond the existence of the signal itself. • A signal is analogous to an interrupt, but it is entirely a software creation. • A signal is generated by a process and transmitted to another process by the operating system. 20EC211- Embedded Systems & IoT
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  Rajasekar T AP/ECE56 Mailboxes • The mailbox is a simple mechanism for asynchronous communication. Some architectures define mailbox registers. • These mailboxes have a fixed number of bits and can be used for small messages. 20EC211- Embedded Systems & IoT
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  Rajasekar T AP/ECE57 20EC211- Embedded Systems & IoT
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  RAJASEKAR T, AP/ECE THANKYOU 20EC211- Embedded Systems & IoT 62