1. This material exempt per Department of Commerce license exception TSU Address Management

2. Address Management 2 Objectives After completing this module, you will be able to: Describe address management for PowerPC  processors Define a system address space Define an advanced user address space Describe the object file sections Describe what a linker script does

3. Address Management 3 Outline Address Management System Address Space Advanced User Address Space Object File Sections Linker Scripts

4. Address Management Embedded processor design requires you to manage the following: – Address map for the peripherals – Location of the application code in the memory space Block RAM External memory Memory requirements for your programs are based on the following: – The amount of memory required for storing the instructions – The amount of memory required for storing the data associated with the program

5. PowerPC Processor Memory and peripherals – PPC405 uses 32-bit addresses Special addresses – Every PowerPC™ system should have the boot section starting at 0xFFFFFFFC Default linker options – Program space occupies a contiguous address space from 0xFFFF0000 to 0xFFFFFFFF – Stack size: 4 KB – Heap size: 4 KB 0x0000_0000 0xFFFF_0000 0xFFFF_FFFC Peripherals PLB/OPB Memory Reset Address

6. Address Management 6 Outline Address Management System Address Space Object File Sections Linker Scripts

7. Advanced User Address Space Different base address, contiguous user address space – The user program can run from any memory PLB, OCM, OPB, or LMB – To execute a program from any address location other than default, you must provide the compiler gcc with a Program Start Address

8. Advanced User Address Space Different base address, noncontiguous user address space – You can place different components of your program in different memories For example, on PowerPC  systems, you can keep your code on instruction cache memory and the data on ZBT memory – Noncontiguous executables that represent the application must be created – To do this, a linker script must be used

9. Address Management 9 Outline Address Management Advanced User Address Space Object File Sections Linker Scripts

10. Object File Sections What is an object file? – An object file is an assembled piece of code Machine language: li r31,0 = 0x3BE0 0000 – Constant data – There may be references to external objects that are defined elsewhere – This file may contain debugging information

11. Address Management 11 Object File Sections.text.rodata.sdata2.data.sdata.sbss.bss Text section Read-only data section Small read-only data section (less than eight bytes) Read-write data section Small read-write data section Small uninitialized data section Uninitialized data section

12. Address Management 12 Object File Sections.init.fini.ctors.dtors.got2.got.eh_frame Language initialization code Language cleanup code List of functions to be invoked at program startup List of functions to be invoked at program end Pointers to program data Frame unwind information for exception handling

13. Address Management 13 Sections Example int ram_data[10] = {0,1,2,3,4,5,6,7,8,9}; /* DATA */ const int rom_data[10] = {9,8,7,6,5,4,3,2,1}; /* RODATA */ int I; /* BSS */ main(){... I = I + 10; /* TEXT */... }

14. Address Management 14 Outline Address Management System Address Space Object File Sections Linker Scripts

15. Address Management 15 Linker Scripts Linker scripts – Control the linking process – Map the code and data to a specified memory space – Set the entry point to the executable – Reserve space for the stack Required if the design contains a discontinuous memory space

16. Address Management 16 Linker and Locator Flows.text1.data1.bss1.bss2.data2.text2 foo1.o foo2.o Link.text.data.bss 0xFFFF 0xF000 0xEFFF 0xEF00 0x0000 0x1FFF 0x2000 0xEEFF Locate Merged Output Sections Unused Executable Image Code uninitialized data Initialized data

17. Address Management 17 Linker Script for the PowerPC Processor Required to control how the program and data are targeted to PLB, OPB, OCM, or extended memory Provide a linker script to the powerpc-eabi-gcc compiler The linker script defines the layout and the start address of each of the sections

18. Address Management 18 Linker Script Limitations Allocate space in the.bss section for the stack and the heap – The stack and the heap must be placed together at the end of the.bss section Ensure that: – The following variables are set to define each section:.sdata: __SDATA_START__, __SDATA_END__.sdata2: __SDATA2_START__, __SDATA2_END__.sbss2: __SBSS2_START__, __SBSS2_END__ – The.sdata and.sbss sections are contiguous – The.boot section starts at 0xFFFFFFFC – The.boot0 section is within a ±24-bit address space of the _boot label – The.vector section is aligned on a 64K boundary

19. Address Management 19 PowerPC Processor Script Example STACKSIZE = 4k; MEMORY { ddr : ORIGIN = 0x00000000, LENGTH = 32m sram : ORIGIN = 0x10000000, LENGTH = 2m flash : ORIGIN = 0x18000000, LENGTH = 32m bram : ORIGIN = 0xffff8000, LENGTH = 32k - 4 boot : ORIGIN = 0xfffffffc, LENGTH = 4 } SECTIONS {.text : { *(.text) } > bram.boot : { *(.boot) } > boot.data : { *(.data) *(.got2) *(.rodata) *(.fixup)} > bram.bss : { *(.bss) } > bram __bss_start = ADDR(.bss); __bss_end = ADDR(.bss) + SIZEOF(.bss); }

20. Address Management 20 Sections Command This is where most of the work takes place Output sections are named, and the input sections are grouped and linked together into the output sections Example: Explanation: –. text is the name of the output section – { *(.text) *.(init) } includes all input sections named text and init from the object files being linked – > bram locates the.text output section in the next available memory in the block RAM area.text : { *(.text) *(.init) } > bram

21. Address Management 21 Linker Script Generator GUI XPS contains a graphical Linker Script Generator Table-based GUI allows you to define the memory space for any section Launch from Software → Generate Linker Script, or from the Applications Tab, right-click on → Generate Linker Script The tool will create a new linker script (the old script is backed up)

22. Address Management 22 Knowledge Check When do you need to use a linker script? What does a linker script do?

23. Address Management 23 Answers When do you need to use a linker script? – When you have software developed in multiple source files and the compiled object code needs to be placed in different memory structures or in nonstandard configurations What does a linker script do? – The linker script controls the placement of the object code, data, stack, and heap in specific memory locations

24. Address Management 24 Knowledge Check What does.sdata2 section contain? What does.sdata section contain? What does.sbss section contain?

25. Address Management 25 Answers What does.sdata2 section contain? – Small read-only data What does.sdata section contain? – Small read-write data What does.sbss section contain? – Small uninitialized data

26. Where Can I Learn More? Tool documentation – Embedded System Tools Guide  Address Management – Embedded Systems Tools Guide  Stand-Alone Board Support Package – Embedded Systems Tools Guide  GNU Compiler Tools Support Website – EDK Website: www.xilinx.com/edkwww.xilinx.com/edk – GNU Website: http://gcc.gnu.org/onlinedocs/gcc-3.4.4/gcc