EE458 - Embedded Systems Lecture 4 Embedded Devel.

Transcription

1 EE458 - Embedded Lecture 4 Embedded Devel. Outline C File Streams References RTC: Chapter 2 File Streams man pages 1

2 Cross-platform Development Environment 2

3 Software available on the host system typically includes a cross-compiler, a linker, and a source-level debugger. Software on the target might include a dynamic loader, a link loader, a a debug agent., and One or more connections allow downloading of program images and debugging. 3

4 Embedded systems development requires much greater knowledge of the target architecture and the compile and link processes than does development for a general purpose OS (GPOS). How is the image transferred? How and where is the image loaded at runtime? How do we the program running on the target? 4

5 On the host system: A compiler or assembler is used to convert source code to object code (.o files). The make program may be used to control the compile and linking processes. A is used to combine object files into an executable image file. 5

6 The different tools that are used on the host to create an executable image. 6

7 Each object file created by the compiler contains a Symbol Table and a. The Symbol Table maps variable and function names to their relative address locations. The contains a list of all addresses that reference symbols in the Symbol Table. 7

8 The Symbol and Relocation Tables 8

9 The linker uses these two tables to convert all relative address references to the actual addresses assigned to the symbols. When creating an executable all references are resolved so that each symbol has an absolute memory address. 9

10 RTEMS images and object files are in the format (Executable and Linking Format) that is described in the text. The binary instructions, binary data, symbol table, relocation table, and debug information are organized and contained in different sections of the file. 10

11 The readelf command displays section types and (edited for readability): $ i386-rtems-readelf -a hello.exe ELF Header: Magic: 7f 45 4c Class: ELF32 Data: 2's complement, little endian Section Headers: [Nr] Name Type Addr Size ES Flg [ 1].text PROGBITS WAX [ 4].data PROGBITS d67 00 WA [ 6].bss NOBITS 0011a aec 00 WA 11

12 Sections of the image can be mapped to particular areas of memory by using MEMORY and commands in a linker script. The developer must, of course, know the types of memory available (ROM, RAM, Flash) and the address of each type in order to write a proper linker script. 12

13 Target System Memory Map 13

14 The GNU linker is ld (i386-rtems-ld for RTEMS development). (See info ld for additional information.) Since we are developing for the PC (whose architecture is well known) we will not have to write special. (You would need to create linker scripts when porting RTEMS to a new BSP.) 14

15 C File Streams Now, on to a completely new topic. RTEMS does not provide implementations of the C++ iostream classes (cin, cout, cerr) Input and output is performed using the traditional (or FILE) streams. 15

16 C File Streams Here is some example code demonstrating I/O with FILE streams: #include <stdio.h> int total = 12000; FILE *myfile = fopen( output.txt, w ); fprintf(myfile, Sum is %d\n, total); fclose(myfile); 16

17 C File Streams The fopen() routine associates a FILE stream with a filename. The first argument is the filename. The second argument is the mode: r, w, a, r+, w+ or a+. See the fopen man page for details. (man 3 fopen) Three streams are automatically opened: stdin, stdout,. #include <stdio.h> fprintf(stdout, Sum is %d\n, total); 17

18 C File Streams The fprintf() routine (man 3 printf) writes variables to a FILE stream in accordance with a format specifier. The format specifier is a char string that contains ordinary text and conversion specifiers. Conversion specifiers begin with a. fprintf(stdout, Name: %s %s\n, fname, lname); fprintf(stdout, Age: %d\n, age); printf( Volt=%f, Current=%f\n, v, i); 18

19 C File Streams The fscanf() routine (man 3 scanf) is used to read variables from a FILE stream in accordance with a format specifier. The of the variable is used as an argument to fscanf(): fscanf(stdin, %s %s, fname, lname); fscanf(stdin, %d, &age); // Note %lf for double %f for float scanf( %lf %lf, &v, &i); 19

20 C File Streams The fputc()/putc()/putchar() routines can be used to write a single character to a stream. The fgetc()/getc()/getchar() routines can be used to read a single char from a stream. sprintf() prints to a char array instead of to a stream. It is useful for converting numbers to. sscanf() can be used to read variables from a char array. 20

21 C File Streams C FILE streams are buffered. Output is not written until the buffer is full or an input routine (fscanf, fgetc, etc) is called. You can flush the output buffer with. When using the input routines (fscanf, fgetc, etc) input is normally not returned to the program until a newline is entered. (The termios routines can be used to change this behavior.) 21