Characteristics of Realtime and Embedded Systems

1. Characteristics of Realtime and Embedded Systems Chapter 1

2. Embedded Systems • Embedded systems are computing systems with tightly coupled hardware and software integration. • Designed to perform dedicated function • Embedded means that the system is a integral part of a larger system • Multiple embedded systems can co-exist in a single system. • General purpose processor are typically not aware of the applications. • An embedded processor is application-aware.

3. Embedded Systems (contd.) • Hardware and software co-design: hardware and software for the embedded system are developed in parallel. • Cross-platform development: Both embedded system and its application use the cross-platform development method. • Software is developed on one platform but runs on another. • Software storage will have to be chosen to allow for upgradeability. • Of course, the SoC, PoE, etc.

4. Realtime Systems Real-time systems Synchronous & Asynchronous Outputs Synchronous & asynchronous Events Timing constraints

5. Real-time Systems • Real-time systems are those systems in which the overall correctness of the system depends on both the functional correctness and the timing correctness. • Realtime systems also have a substantial knowledge of the system it controls and the applications running on it. • Deadline dependent. • Predictability is important.

6. Hard and soft Real-time Systems • A hard real-time systems is a real-time system that must meet its deadlines with a near zero degree of flexibility. Deadlines must be met, otherwise catastrophes occur. • A soft-time system is a real-time system that must its deadlines but with a degree of flexibility. The deadlines contains various levels of tolerance, even statistical distribution of response times with different degrees of acceptability. • An important requirement: scheduling algorithms

7. Real-time Embedded Systems RTS EMB RTEMB Railway monitoring and scheduling : RTS Cell phone: EMB Heart pacemaker: RTSEMB

8. Chapter 2: Basics of Development for Embedded Systems • Typical cross-platform development environment • Host system: essential tools are cross compiler, linker, source level debugger • Executable image contains RTOS, Kernel, application program: compiled and linked • Target system: where to store the executable image, and how? • Connections: ethernet and serial • See figure 2.1

9. Making of an Executable • Makefile • Demo

10. Compile and Link • Compiler converts the high level language code into native machine code or object code • Linker does symbol resolution and symbol relocation to generate the executable code: • See Figure 2.3 • Symbol resolution is the process by which the linked goes through each object file and determines where the external symbols in it are located. Then it copies the required file into the final image. • Symbol relocation is the process in which the linker maps symbol reference to its definition.

11. ELF (Executable Linker Format) • An object file contains: • file size, binary code, data size, source file name and other general information • Machine architecture specific binary instructions and data • Symbol table and relocation table • Debug information, which the debugger uses • There are standards for organizing object file formats. ELF is very commonly used format.

12. ELF (contd.) • Compiler organizes the compiled code into system-defined as well as user-defined content groupings called sections. • Example sections: binary code, symbol table • Each section also has important information about load address and run address. • Section header and program header: Listing 2.1 • A section header table is an array of section header sections of an object file. • A program header table is array of program header structures describing a loadable segment of an image. `

13. Section Types (sh_types) • PROGBITS code or initialized data • SYMTAB etc. • Some common system created default sections are: .text, .data, .sdata • Section attributes (sh_flags) : WRITE, ALLOC, EXECINSTR • sh_addr is the section address and p_addr is the program address on the target machine

14. User defined sections • You could add user-defined sections: .section mysection If you were to create the embedded program from scratch you will define it in terms of sections as defined above. Remember the .data and .text sections from your MIPS code (of cse341).

15. Mapping Executable Images into Target Embedded Systems • Multiple source files (C/C++, assemble) have been compiled and assembled into object files, a linker must combine these object files and merge sections from different object files into program segments. • The process creates a single executable image for the target embedded system. • Embedded system developer uses linker directives to control how the linker combines sections and allocates segments into target system. • Common directives are MEMORY and SECTION (see examples Listing 2.2 and 2.3)

16. Memory Map of the Target System • See fig 2.5 and compare it with MEMORY directive listing 2.2 • Also check out the memory map of XINU • Section .text can be mapped to ROM, Flash or Ram where the section .data has to be mapped to RAM.

17. Generating Executable Image • Combining multiple sections into executable image: fig. 2.6 • Mapping executable image into target memory fig 2.7 • Module upgradability through flash memory. • Use SDRAM for code /data that require fast access and DRAM for the rest of the code/data. • See Listing 2.5 and Figure 2.8 for examples.