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ARM 2007 Chapter 10 Firmware Optimization Technique in Embedded System (ARM) 2008 April.

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Presentation on theme: "ARM 2007 Chapter 10 Firmware Optimization Technique in Embedded System (ARM) 2008 April."— Presentation transcript:

1 ARM 2007 Chapter 10 Firmware Optimization Technique in Embedded System (ARM) 2008 April

2 ARM 2007 Overview Firmware is an important part of any embedded system –Since it is frequently the first code to be ported and executed on a new platform. –Firmware can vary from being a complete software embedded system to just a simple initialization and Bootloader routine. Agenda –Firmware & Bootloader –General Process of a firmware –ARM Firmware Suite –Redboot (Redhat) –Sandstone (Sloss)

3 ARM Firmware and Bootloader

4 ARM 2007 Definitions We realize that the use of terms may differ among engineers, but we will use the following definitions –The firmware : an interface between the hardware and the application/operating system level software. »It resides in the ROM and executes when power is applied to the embedded hardware system. »It can remain active after initialization to support basic system operation. –The bootloader is a small application that installs the operating system or applications onto a hardware target. »The bootloader only exists up to the point that the operating system or application is executing, and it is commonly incorporated into the firmware.

5 ARM 2007 Abstraction of Firmware Execution Flow To help understand the features of different firmware implementations, we have a common execution flow.

6 ARM 2007 I-a. Identify the platform It’s common for the same executable to operate on different cores and platforms. –In this case, the firmware has to identify and discover the exact core and platform it is operating on. »CP15:r0 = processor type, manufacture name »Platform identification: a set of particular peripheral.

7 ARM 2007 I-b. Diagnosing Diagnostics software provide a useful way for quickly identifying basic hardware malfunctions. Debug capability is provided in the form of a module or monitor. –Setting up breakpoints in RAM; –Listing and modifying memory (peek & poke); –Showing current processor register contents; –Disassembling memory into ARM or Thumb mnemonics. Interactive method –CLI (command line interpreter) (via RS-232) –A dedicated host debugger (via LAN + C/S) Unless the firmware has access to the internal hardware debug circuitry, only RAM image can be debugged through a software debug mechanism.

8 ARM 2007 II. HAL The second stage is to abstract the hardware. –The Hardware Abstraction Layer (HAL) is a software layer that hides the underlying hardware by providing a set of defined programming interfaces. –The HAL software that communicates with specific hardware peripheral is call a device driver. »A device driver provides a standard application programming interface (API) to read and write to a specific peripheral.

9 ARM 2007 III. Load a bootable image The ability of firmware to carry out this activity depends upon the type of media used to store the image. –Note that NOT all operating system images or application images need to be copied into RAM, they could be executed directly from ROM (XIP). –FFS: flash ROM filing system. –Network File System Image Format –Plain binary: doesn’t contain any header or debug information. –Executable and Linking Format (ELF) »developed for UNIX, and replaced the COFF. »ELF files come in three forms: relocatable, executable, and shared object. –Compressed image

10 ARM 2007 IV. Relinquish Control This is where the firmware hands over control of the platform to an operating system or application. –Note that NOT all firmware hands over control. Alternatively, the MIL or HAL part of firmware can remain active. This layer expose, through SWI mechanism, a standard application interface for specific hardware devices. Relinquishing control means –Updating the vector table and modifying the PC. –Passing Environment Data Structure (EDS) to some sophisticated OS, e.g., Linux. »EDS fields: memory size, MMU type, etc.

11 ARM ARM Firmware Suite ARM Firmware Suite (AFS) –Support ARM processors including Intel’s Xscale and StrongARM –Two technologies: uHAL and Angel (monitor) micro-HAL and API –Initializing, UART Driver, LED Control (for Indicating) –Timer (for preemptive context switching) –Interrupt Controller (IC) (many types supported) Angel –Comm. between host and target (debug/develop ) –CLI (for command) –APIs (via SWI)

12 ARM Redboot RedBoot –Redhat, Open Source License –CPU: ARM, MIPS, SH –HAL is heart of Redboot It provide both GDB (debug) and Bootloader RedBoot supports three main features –Communication: X-Modem, TCP, bootp, telnet, tftp –Flash Management: Download, Update, Flush –Full OS Support: Linux, eCos (Redhat) »Passing parameters

13 ARM Example: Sandstone A minimal system

14 ARM 2007 A Real Case: Sandstone It carries out only the following task (simple) –Setting up target platform; –Loading a bootable image; –Relinquish control to OS. Implementation –It is specific to the ARM Evaluator-7T platform. –This example shows you How a simple platform be set.

15 ARM Directory layout of Sandstone Directory Structure in Sandstone

16 ARM 2007 More./obj/Makefile –OBJS = sand.o –all : ${OBJS} –armlink -o../image/sand.elf ${OBJS} –fromelf -bin -o../image/rom.bin../image/sand.elf –sand.o :../src/sand.s –armasm -o $<

17 ARM Sandstone Code Structure Sandstone consist of a single assembly file –The file structure is broken down into a number of steps, where each step corresponds to a stage in the execution flow of Sandstone.

18 ARM Take the Reset Exception –AREA start,CODE,READONLY –ENTRY –start_sandstone –Bsandstone_init1 –Bex_undef –B ex_swi –Bex_pabt –Bex_dabt –NOP; bad code (will fall through) –Bint_irq –Bint_fiq –ex_undefB ex_undef; loop forever –ex_swiBex_swi –ex_dabtBex_dabt –ex_pabtBex_pabt –int_irqBint_irq –int_fiqBint_fiq

19 ARM Start Initializing the Hardware The primary phase in initializing hardware is setting up system registers. –SYSCFG EQU 0x03FF0000 –sandstone_init1 –LDRr3, =SYSCFG –LDRr4, =0x03FFFFA0 ; b[31:16]=base, [15:0]=cfg » ; Disable both the “cache” and “write-buffer” –STRr4, [r3] – ……... –B sandstone_memorycode Note –SYSTEM is a self-reference register. Its default address is 0x3ff00000 (arch-dependent).

20 ARM Remap Memory As you see, –when the platform is powered up, only ROM is assigned a location in the memory map. –The two SRAM bank (0 and 1) are not available. We should –bring in the two SRAM banks, and –remap the ROM to a new location

21 ARM 2007 Remap the ROM, and Setup SRAM –LDRlr, =sandstone_init2 –LDRr4, =0x –ADDlr,lr,r4; calculate the absolute address –ADRL r0, memorymaptable_str ; get address of table –LDMIA r0, {r1-r12} –LDRr0, =EXTDBWTH ; =(SYSCFG + 0x3010) –STMIA r0, {r1-r12}; setup DBus Width –MOVpc, lr; JUMP to remapped memory –memorymaptable_str – DCD rEXTDBWTH ; ROM0(Half), ROM1(Word), ROM1(Word), rest Disabled – DCD rROMCON0 ; 0x ~ 0x , RCS0, 4Mbit, 4cycle, ROM – DCD rROMCON1 ; 0x ~ 0x , RCS1, 256KB, 2cycle, SRAM1 – DCD rROMCON2 ; 0x ~ 0x , RCS2, 256KB, 2cycle, SRAM2 * Question: Here, ROM has already remapped to higher memory space, how can this instruction “MOV pc, lr” be fetched? (*)

22 ARM Initialize Communication Hardware Communication initialization involves –Configuring a serial port, and –Outputting a banner message on console The serial port is set to –9600 baud, no parity, one stop bit, and no flow control

23 ARM 2007 UART (1) –sandstone_init2 –B sandstone_serialcode –sandstone_serialcode –// UART Control: Clearing –LDR r1, =UART0_BASE – ADD r1, r1,#UCON – MOV r2, #0 – STR r2, [r1] –// Line Control: 7/8-bit, 1/1.5-Stop, No/Odd/Even-Parity –LDR r1, =UART0_BASE – ADD r1, r1,#ULCON – MOV r2, #ULCR8bits – STR r2, [r1]

24 ARM 2007 UART (2) –// UART Control: Loop-back, DMA, INT, Tx/Rx Enable –LDR r1, =UART0_BASE – ADD r1, r1, #UCON – MOV r2, #(UCRRxM | UCRTxM) – STR r2, [r1] – –// Baud-Rate –LDR r1, =UART0_BASE – ADD r1, r1, #UBRDIV – MOV r2, #(BAUD_9600) – STR r2, [r1]

25 ARM 2007 UART (3) Printing banner –ADRLr0,sandstone_banner –print_loop –print_wait –LDRr3,=UART0_BASE –ADDr3,r3,#USTAT –LDRr4,[r3] –MOVr5, #USRTxHoldEmpty –ANDr4,r4,r5 –CMPr4,#0 –BEQprint_wait –

26 ARM 2007 UART (4) Printing char –// PUT CHAR (*(unsigned *)((p) + UTXBUF) = (unsigned )(c)) –LDR r3,=UART0_BASE –ADDr3,r3,#UTXBUF –STRr1,[r3] –LDRBr1,[r0] –ADDr0,r0,#1 –CMP r1,#0 –BNEprint_loop –B sandstone_load_and_boot –sandstone_banner –DCB"\n\r*\n\r" –DCB "\n\rSandstone Firmware (0.01)\n\r" –DCB"- platform e7t\n\r" –DCB"- status alive\n\r" –DCB "- memory remapped\n\r" –DCB"\n\r+ booting payload...",0

27 ARM Bootloader Copy Payload and Relinquish Control –ALIGN 4 –sandstone_load_and_boot –// Section 1 : Copy payload to address 0x –MOVr13,#0; destination addree –LDRr12,payload_start_address; start address –LDRr14,payload_end_address; end address –block_copy –LDMIAr12!,{r0-r11} –STMIA r13!,{r0-r11} –CMPr12,r14 –BLEblock_copy

28 ARM 2007 Relinquish Control –// Section 2 : Relinquish control over to the payload –MOVpc,#0; – LTORG; Don’t take literal data as code –payload_start_address –DCD startAddress –payload_end_address –DCD endAddress –startAddress – INCBIN../../payload/slos.bin –endAddress –END Notes –LTORG: indicates a “literal pool”, data (constants) are accessed with PC-offset (within 4KB), rather than from DATA section. –INCBIN: load into a payload in file style.

29 ARM Summary This chapter covered the firmware –We define firmware as the low-level code that interfaces the hardware with an application or operating system. –We also define bootloader as the software that loads an operating system or application into memory and relinquishes control of the PC to that software. –We introduced the ARM Firmware Suite (AFS) and RedBoot. –Next, we looked at a firmware example called Sandstone. »Sandstone initialized the hardware and then loads and boots an image following this procedure: Take the reset exception Starts initializing the hardware; sets the system register’s base address and initializes segment display hardware. Remaps memory; ROM address = high, and SRAM addr = 0x Initializes the communication hardware output on the serial port. Bootloader – loads an image into SRAM and relinquishes control of the PC to the image (PC=0x ). We now have a fully initialized ARM7TDMI embedded system.


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