Porting FreeRTOS on OpenRISC

Porting FreeRTOS on OpenRISC

Speaker：Yi-Chiao Lin

• Motivation

• OpenRISC

• Porting FreeRTOS on OpenRISC

• Experiments

Outline

Multi-Tasking Management Support

• Round-Robin 、 FIFO ……

Memory Management Unit Support

• TLB、Page Table ……

On-chip Memory Architecture Support

• Cache and SPM (scratch pad memory)

Motivation

Scratch Pad Memory(SPM)

• Software controlled on-chip memory

• Consume less energy than cache

SPM (scratch pad memory)

• Motivation

• OpenRISC

• Porting FreeRTOS on OpenRISC

• Experiments

Outline

Or1200 Open Hardware CPU released

Implemented in the Verilog

5-stage pipeline

32 register

Special-Purpose Registers

OpenRISC

l.mfspr / l.mtspr

MMU、Cache、Interrupt……

OpenRISC

Enable/Disable

• Motivation

• OpenRISC

• Porting FreeRTOS on OpenRISC

• Experiments

Outline

Real time operating system

Designed to be small and simple(2k~3k)

Stack can be shared between tasks

For free!!

FreeRTOS benefit

Task Create

xTaskCreate(

pdTASK_CODE pvTaskCode,

const portCHAR * const pcName,

unsigned portSHORT usStackDepth,

void *pvParameters,

unsigned portBASE_TYPE uxPriority,

xTaskHandle *pvCreatedTask )

void vRtosTask(void *pvParameters){

while(1){

.........

}

}

Task

xTaskCreate

prvAllocateTCBAndStack( usStackDepth, puxStackBuffer

);

prvInitialiseTaskLists();

prvInitialiseTCBVariables( pxNewTCB, pcName, uxPriority, xRegions,

usStackDepth );

prvAddTaskToReadyQueue( pxNewTCB );

• FreeRTOS porting file :

1. Port.c

2. Portmacro.h

3. Portasm.S

4. Port_spr_def.h(OpenRISC)

(Definition of special-purpose registers)

FreeRTOS/Source/portable/[Platform]

FreeRTOS Porting

FreeRTOS Porting

Ported layer Port.c Portmacro.c Portasm.S Port_spr_def.h

Kernel layer

Application layer

Pagetable.c

TLB-miss ISR

Software(FreeRTOS)

Timer ISR

task.c

Data Moving ISR TLB.c

cache.c Interrupt handler

Reset.S

Hardware(OpenRISC) SPM Redirector

Page miss

Bookkeeping

Port_spr_def.h

Portmacro.h

Define Kernel Type

pxPortInitialiseStack

vPortDisableInterrupts

vPortEnableInterrupts

prvSetupTimerInterrupt

xPortStartScheduler

port.c

port.c (*pxPortInitialiseStack)

PxCode

uTaskSR

r31:0x00000031

r30:0x00000030

r29:0x00000029

.

.

.

High address

Low address

vPortDisableInterrupts

vPortEnableInterrupts

port.c

Exception Handler Exception type Vector offect[11:0] Example

Reset 0x100 Caused by Software or

Hardware reset

Bus error 0x200

Data Page fault 0x300

Instruction Page fault 0x400

Tick Timer 0x500 Timer interrupt

Alignment 0x600

Illegal Instruction 0x700

External interrupt 0x800 External interrupt asserted

D-TLB miss 0x900 No matching entry in DTLB

I-TLB miss 0xA00 No matching entry in ITLB

Range 0xB00

System call 0xC00

Float Point 0xD00

Trap 0xE00

Exception Program Counter Registers

Exception Supervision Registers

Exception Effective Address Register

Exception Register

Maximum timer count of 2^32 clock cycles

Tick Timer

TTMR

TTCR

RISC Clk Tick INT

Tick Timer Mode Register

Tick Timer Counter

prvSetupTimerInterrupt

Port.c

xPortStartScheduler

Task 1

Task2

Memory

Stack_TCB

Stack_TCB

Setup Timer

Load register

Load TCB

• Context Switch

portSAVE_CONTEXT

portRESTORE_CONTEXT

Portasm.S

Task1 Task2

Stack_TCB Stack_TCB

Portasm.S (Tick Handler)

Reset register

Set Stack point、Clear BSS

Reset Cache、MMU、UART

Reset.S(Booting)

OpenRISC Start at 0x100

Clear general-purpose registers

Reset register

Set Stack Pointer

Clear BSS

Clear BSS (Block Started by Symbol)

• Flush Cache

Data Cache Block Invalidate Register

Cache

D-cache 8k 512Line 4word

PPN[31:13] 0x1[12:4] 0x8[3:0]

Physical [31:13]

Physical [31:13]

Physical [31:13]

Physical [31:13] WORD

WORD

WORD

WORD

WORD

Physical [31:13] V

V

V

V

V WORD

WORD

WORD

WORD 0

1

2

3

4

5

6

7

2047

0

1

2

3

511

13:2 12:4

Task address space isolation

Allow safe sharing of memory among multiple tasks

Why OS need MMU Support?

CPU

Task1

Task2

Virtual

Task 1

Task2

Memory

Physical

Page Index Level 1[31:24] Page Offset[12:0] Page Index Level 2[23:13]

0

255

PTE

PTE2

+

0

2047

Physical Page Number Page Offset[12:0]

+

Address

Page Table entry

Physical Page Number D A WBC CI CC WOM W R W R REV

Entry Store in Memory

Set in Data Translation Lookaside Buffer Translate Registers when

DTLB-MISS

TLB miss Handler

TLB MISS

Find the Task

Find Page Table

Set TLB register

Exception Effective Address Registers

or1200_except.v

Exception Effective Address Registers

DTLB Architecture

Virtial address[19:31] Index[13:18] Offset[12:0]

VPN [19:31] V

VPN [19:31] V

VPN [19:31] V

VPN [19:31] V

PPN [13:31]

PPN [13:31]

PPN[13:31]

PPN [13:31]

PPN [13:31] VPN [19:31] V

Direct mapped

相等

&& V=1

Physical address[13:31] Offset

DTLB miss

DTLB Match Register

DTLB Translate Regidter

EEAR:0x6000

W R W R CI

W R W R CI

W R W R CI

W R W R CI

W R W R CI

Super User

W R W R CI

Waveform

DTLB Miss

0x900

Interrupt ->

Dmmu Disable

0x100->0x20000100

Interrupt ->

Dmmu Disable

0x100->0x20000100

FreeRTOSConfig.h

Set Total Stack、SYSCLK……

• Set Uart Base Address、System CLK……

• Cache size set……

Board.h

Modify OpenRISC memory architecture

CPU

D-MMU

Data ram

Wishbone bus

Redirector

D-Cache SPM

Page miss

Bookkeeping

circuit

Interrupt

PIC (Programmable Interrupt Controller)

Page miss

Bookkeeping

circuit

or1200_cpu.v external_interrupt.v

or1200_pic.v

spr_cs

spr_we

spr_addr

spr_dat_i

intr

spr_dat_o

clk

rst

pic_int[31:0]

SPM data moving interrupt handler

Free SPM

space?

Interrupt

Select a victim page and

move it to Data ram

Move the page into SPM

No

Yes

Update D-TLB

Translate Regidter

Update Page table

• Motivation

• OpenRISC

• Porting FreeRTOS on OpenRISC

• Experiments

Outline

Verify on FPGA Board

Verify on FPGA Board

VeriComm

Dump Counter

學習移植OS與底層硬體的整合

善加運用身邊工具Debug

更加了解CPU之運作

Summary

Thank You for Listening

Contact us.

E-mail : joe21013@hotmail.com