FreeRTOS overview and experience

1.1 FreeRTOS Directory structure

With Keil Under the tools STM32F103 Chip as an example , its FreeRTOS Directory as follows ：

Mainly involves 2 A catalog ：

• Demo
  • Demo Under the directory is the project file , With “ Chips and compilers are combined into one name ”
  • such as ：CORTEX_STM32F103_Keil 
• Source
  • The root directory is the core file , These documents are FreeRTOS Source code , These files are generic
  • portable Directories are files that need to be implemented during migration , Hardware interface layer ,FreeRTOS And the chip .
    • The directory name is ：[complier]/[architecture]
    • such as ：RVDS/ARM_CM3, This means cortexM3 Architecture in RVDS Migration files on tools

1.2 Core documents

FreeRTOS Strictly speaking, the most core document of is 2 individual ：

• FreeRTOS/Source/task.c 
• FreeRTOS/Source/list.c

Broad sense of queue.c It is often used , But it's not necessary , Some places also put queue.c This document is also considered necessary .

The functions of other documents are also listed as follows ：

FreeRTOS/Source The files under the	effect
tasks.c	It's necessary , Task operation
list.c	It's necessary , The list of operations
queue.c	Basically , Provides queue operations , Semaphore （semaphore） operation
timer.c	Optional ,software timer
event_groups.c	Optional , Provide event group function
croutine.c	Optional , coroutines ,FreeRTOS No more updates , Out of date

1.3 Files involved in migration

transplant FreeRTOS The documents involved are placed in FreeRTOS/Source/portable/[complier]/[architecture] Under the table of contents ,

such as ：RVDS/ARM_CM3, This means cortexM3 Architecture in RVDS or Keil Migration files on tools

There are 2 File ：

• port.c
• portmacro.h

1.4 Header file related

1.4.1 Header Directory

FreeRTOS Three header directories are required ：

• FreeRTOS Own header file ：FreeRTOS/Source/include
• Header files used in migration ,FreeRTOS/Source/portable/[complier]/[architecture]
• With configuration file FreeRTOSConfig.h The catalog of

1.4.2 The header file

The header file	effect
FreeRTO\quSConfig.h	FreeRTOS Configuration file for , For example, select a scheduling algorithm ：configUSE_PREEMPTION Every demo Must contain FreeRTOSConfig.h It is suggested to modify demo Medium FreeRTOSConfig.h, Instead of writing from scratch , In fact, this file is provided for users to tailor FreeRTOS System , Defined as needed
FreeRTOS.h	Use FreeRTOS API Function time , This file must be included , stay FreeRTOS.h after , Then include other header files , such as ：task.h、queue.h、semphr.h、event_group.h

1.5 memory management

The file in FreeRTOS/Source/portable/MemMang Next , It is also placed in portable Under the table of contents , Means that you can provide your own functions .

The source code provides... By default 5 File , Corresponding to memory management 5 Methods .

file	advantage	shortcoming
heap_1.c	Assignment Brief , Time is set	Allocate only, do not recycle
heap_2.c	Dynamic allocation , Best match	debris , Time is uncertain
heap_3.c	Call standard library functions	Slow speed , Time is uncertain
heap_4.c	Adjacent free memory can be merged	It can solve the problem of fragmentation , Time is uncertain
heap_5.c	stay heap_4 Support separate memory blocks based on	It can solve the problem of fragmentation , Time is uncertain

1.6 Demo

Demo The directory is pre configured , No compilation errors in the project , The purpose is that you can modify based on it , To fit your board .

these Demo You can also continue to streamline , So that FreeRTOS It looks clean and refreshing .

1.7 Data types and programming specifications

Each migrated version contains its own portmacro.h The header file , It's defined in it 2 Data types ：

• TickType_t: 
  • FreeRTOS A periodic clock interrupt is configured ：Tick Interrupt
  • Every time an interrupt occurs , The number of interrupts is accumulated , This is known as tick count
  • tick count The type of this variable is Tick Type_t
  • Tick Type_t It can be 16 Bit , It can also be 32 Bit
  • FreeRTOSConfig.h In the definition of configUSE_16_BIT_TICKS when ,TickType_t Namely uint16_t
  • otherwise TickType_t Namely uint32_t
  • about 32 An architecture , Make a proposal to TickType_t Configure to uint32_t
• BaseType_t:
  • This is the most efficient data type of the architecture
  • 32 Bit architecture , It is uin32_t
  • 16 Bit architecture , It is uint16_t
  • 8 Bit architecture , It is uint8_t
  • BaseType_t Usually used as a simple return value type , And logical values , such as pdTRUE/pdFALSE

1.7.2 Variable name

Variable names are prefixed

Variable name prefix c	meaning
c	char
s	int16_t .short
l	int32_t,long
x	BaseType_t, Other non-standard types ： Structure ,task handle、queue handle etc.
u	unsigned
p	The pointer
uc	uint8_t , unsigned char
pc	char The pointer

1.7.3 Function name

The prefix of the function name is 2 part ： return type , In which file do you define .

Function name prefix	meaning
vTaskPrioritySet	return type ：void stay task.c In the definition of
xQueueReceive	return type ：BaseType_t stay queue.c In the definition of
pvTimerGetTimerID	return type ：pointer to void stay timer.c In the definition of

1.7.4 Macro name

The name of the macro is capitalized , You can add a lowercase prefix . Prefixes are used to denote ： In which file are macros defined .

Prefix of macro	meaning ： Define... In that file
port( such as portMAX_DELAY)	portable.h or portmacro.h
task( such as taskENTER_CRITICAL())	task.h
pd( such as pdTRUE)	projdefs.h
config( such as configUSE_PREEMPTION)	FreeRTOSConfig.h
err（ such as errQUEUE_FULL）	projdefs.h

The general macro definition is as follows ：

macro	value
pdTRUE	1
pdFALSE	0
pdPASS	1
pdFAIL	1