21天移植FreeRTOS 到Raspberry Pi 2

1. FreeRTOS嵌入式系統移植研究
21天移植FreeRTOS
組長 :黃0閔
組員 :陳0丞、郭0澤、高0穎
專題指導老師 : Joseph
105 艾鍗科技嵌入式Linux系統工程師人才養成班
105 艾鍗科技嵌入式Linux系統工程師人才養成班

2. 21DAYS FREERTOS PORTING ON
RASPBERRY PI2
•Raspberry Pi2:
900 MHz quad core ARM Cortex-A7 CPU
1GB RAM
4 USB ports
40 GPIO pins
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3. WHAT IS RTOS
•General purpose OS:
• Linux
• Windows
•Real-Time OS (RTOS):
• Without buffering delays
• Hard real-time
• Soft real-time
Hard real-time Soft real-time
Program no response while landing
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4. TODAY RTOS ON MCU
• MCU:
• Data bus
From 8bit to 32bit
• CPU clock
ARM Cortex-M (60MHz ↑)
• RTOS:
Multi-task
Small code size
RTOS
TasksTasks TasksTask
MCU & Peripheral
Peripheral Drivers
MCU & Peripheral
Peripheral Drivers
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5. RTOS FEATURE
•Task scheduler:
Task create
Task save
Task restore
Invoke task switch (timer interrupt)
Task communication:
Queue, semaphore,…etc
• Memory Management
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6. RTOS
• RTOS:
• FreeRTOS, QNX, uC/OS, RTEMS
• FreeRTOS:
Free open source
Small: 9000 lines code
Simple : Only 3 ~ 4 files for porting
Multi-platforms：ARM-M series, ARM7, Cortex-A(A8, A9)
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7. DEVELOPMENT TOOL
• IDE:
Eclipse-cdt 4.4.2
• Toolchain:
gcc (arm-none-eabi-4.9)
• Debug Tool:
ICE, J-link, nu-link, st-link
LED, UART
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8. ARM BOOT AND INTERRUPT
_start:
Usually start from 0x0000
Interrupt table
0x0000~0x001C (7 mode)
rest:
Basic hardware, memory
initialize and jump into OS
main function
0x00
…
…
0x1C
Interrupt
Table
RAM
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9. ARM INTERRUPT
Enter IRQ
Disable IRQ
spsr_irq = cpsr
pc = 0x18
IRQ Handler
IRQ function
Leave IRQ
Enable IRQ
pc=LR - 4
spsr =
spsr_irq
0x00
0x04
0x08
0x0c
0x10
0x14
0x18
0x1C
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10. SIMPLE RASPBERRY PI BOOT
• PI GPU Boot
• Black magic(closed source)
• GPU, memory, clock initialize
• Parse config.txt
• Linux Boot
• Load cmdline.txt and Linux kernel
• Send boot argument to linux kernel
• Start from 0x8000
PI GPU Boot
Linux Boot: 0x8000
Shell
FreeRTO
S
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11. COMPILE A PROGRAM
Stage 1 Stage 2 Stage 3
Stage1
• Generate object file
Stage 2
• Put object together
Stage 3
• Output binary file
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12. LINKER SCRIPT
•Put things to section
init, text, data, bss
•Assign section address
Put init to INIT_RAM: 0
INIT_RAM start: 0x8000
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13. FREERTOS BOOT
_start:
Start from 0x8000
Interrupt table
0x8000~0x801C (7 mode)
rest:
Move interrupt table to 0x0000
Initial interrupt stack
0x0000
…
…
0x001C
BCM2836
Interrupt
Table
Memory
0x8000
…
…
0x801C
FreeRTOS
Interrupt
Table
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14. FREERTOS FOR PI2 BOOT
•Interrupt failed
Hyper mode
•Make interrupt work
• Go back to SVC
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15. BCM2836 INTERRUPT
BCM2836 Interrupt
Controller
Peripherals
GPIO
UAR
T
TIME
R
ARM
FIQ IRQ
Enter IRQ
Disable IRQ
spsr_irq = cpsr
pc = 0x18
IRQ Handler
BCM2836 IRQ
Controller
Handler
Leave IRQ
Enable IRQ
spsr = spsr_irq
pc=LR - 4
….
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16. FREERTOS PORTING TODO LIST
Hardware config:
FreeRTOSConfig.h
portmacro.h
Hardware TIMER IRQ:
port.c
portISR.c
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17. FIRST STEP PORTING
GPIO
• LED
• Boot
• Linker script
UART
• Debug
Interrupt
• Timer IRQ
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18. BOOT LOADER U-BOOT
Debug & Build
Power off
Put image to SD
card
Plug in SD
Test
Debug &
Build
U-boot tftp
get
U-boot
load
Test
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19. FREERTOS IRQ INTERRUPT
Enter IRQ Mode
Save Task
Timer Handler
FreeRTOS tick
increase
Context switch if
needed
Leave IRQ Mode
Restore Task
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20. FREERTOS PORTING
•Implement Timer Handler
• FreeRTOS tick increase
• Context switch if needed
•Install FreeRTOS as IRQ Handler
• Save Task
• Restore Task
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21. FREEROTS PORTING FLOW
Develop
Environment
• IDE
• Toolchain
• Debug tool
Basic
knowledge
• Boot startup code
• Linker script
• Interrupt setting
Basic drivers
• LED
• GPIO
• Interrupt
FreeRTOS
• Timer ISR as tick
service
• FreeRTOS as IRQ
handler
FreeRTOS
Application
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22. FREERTOS DEMO
Basic task communication demo:
1 task send
1 task receive (toggle LED)
Application demo:
CLI(Command Line Interface)
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23. Thanks for your attention
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