Topic 10 10/24/2010. C with Embedded Extension

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Mercy McCarthy
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1 Topic 10 C with Embedded Extension Compiler MCC 18 Microchip PICC 18 Hi-Tech Concerns in embedded C programming Limited memory resources - always use the smallest possible variable necessary Smaller data RAM than program mem whenever possible, use constant strings that reside in program mem Slower operation try to avoid the use of multiplies and divides Program efficiency keep in mind the resulted assembly from C GECE502 Embedded C Programming 1 GECE502 Embedded C Programming 2 ANSI C auto, extern, static, register New type in PIC C: overlay apply to local variables, may never be applied to function parameters, function definitions, and global variables variable can share memory space if functions are never active at the same time int f (void) { overlay int x = 1; return x; int g (void) { overlay int y = 2; return y; int f (void) { overlay int x = 1; return x; int g (void) { overlay int y = 2; y = f (); return y; PIC C18 compiler decides local variable x and y can share the same memory location if f() and g() are never called simultaneously x and y can NOT share the same memory location, why? GECE502 Embedded C Programming 3 GECE502 Embedded C Programming 4 1

2 ANSI C const, volatile New in PIC C: near, far, rom, ram GECE502 Embedded C Programming 5 GECE502 Embedded C Programming 6 Program memory code: contains executable instruction romdata: contains variables and constants in program memory Data memory udata: contains statically allocated uninitialized user variables idata: contains statically allocated initialized user variables (continue) rom int ri; rom char rc = 'A'; int ui; char uc; int ii = 0; char ic = 'A'; void foobar (void){ static rom int foobar_ri; static rom char foobar_rc = 'Z'... void foo (void){ static int foo_ui; static char foo_uc;... void bar (void){ static int bar_ii = 5; static char bar_ic = 'Z';... GECE502 Embedded C Programming 7 GECE502 Embedded C Programming 8 2

Use pragmas to change the current section into specified type. A section is a portion of an application located at a specific address of memory. Sections can contain code or data.

3 Use pragmas to change the current section into specified type. A section is a portion of an application located at a specific address of memory. Sections can contain code or data. A section can be located in either program or data memory. There are two types of sections for each type of memory. #pragma sectiontype [attributes] [sectionname[=address]] sectiontype udata: uninitialized variable in data memory idata: initialized variable in data memory code: executable instructions in program memory romdata: variables or constants in program memory attributes access: access bank overlay: sharable memory sectionname: C identifier address: integer, specifies the absolute address in program or data memory GECE502 Embedded C Programming 9 GECE502 Embedded C Programming 10 Access section will be put in the access bank in data memory Variables located in an access section must be declared with the near keyword. Example: #pragma udata access my_access /* all accesses to these will be unbanked */ near unsigned char av1, av2; Overlay section in data or program memory can be shared Example: file1.c: #pragma code overlay my_overlay_scn=0x1000 void f (void){... #pragma udata overlay my_overlay_data=0x1fc int int_var1, int_var2; /* 2 bytes at 0x1fc and 0x1fe */ file2.c: #pragma code overlay my_overlay_scn=0x1000 void g (void){... #pragma udata overlay my_overlay_data=0x1fc long long_var; /* 4 bytes located at 0x1fc */ Pointers can point to either data memory (ram pointers, default) or program memory (rom pointers). The size of a pointer is dependent on the type of the pointer rom pointers and ram pointers are not compatible GECE502 Embedded C Programming 11 GECE502 Embedded C Programming 12 3

The processor-specific header file includes a structure definition that allows the user to access individual bits of a register by: appending bits to the register name appending a period to the

4 The processor-specific header file includes a structure definition that allows the user to access individual bits of a register by: appending bits to the register name appending a period to the symbol resulted in step 1 specifying the bit name after the period For example, Refer to PIC18Fxx2Datasheet.pdf for more details PORTBbits.RB0 = 1; /* pull PORTB bit 0 to high */ PORTBbits.RB1 = 0; /* pull PORTB bit 1 to low */ STATUSbits.C = 0; /* clear the C flag to 0 */ GECE502 Embedded C Programming 13 GECE502 Embedded C Programming 14 void MCU_init() { /* setup I/O ports */ ADCON1 = 0b ; TRISD = /* setup Timer0 */ // Enable PORTE digital I/O pins T0CON = 0b ; //Timer0 off, 16 bit timer, internal //source, 1:32 prescale... /* Configure Timer0 and Timer1 interrupts */ RCONbits.IPEN = 0; //disable interrupt priority INTCONbits.GIE = 1; //enable all interrupts INTCONbits.PEIE = 1; //enable all peripheral interrupt INTCONbits.TMR0IE = 1; INTCONbits.TMR0IF = 0; //enable Timer0 interrupt //clear Timer0 interrupt flag PIE1bits.TMR1IE = 1; //enable Timer1 interrupt PIR1bits.TMR1IF = 0; //clear Timer1 interrupt flag /******************************* * GenerateMsec() *******************************/ void GenMsec() { flags.msec_done = 0; TMR1H = 0xec; TMR1L = 0x78; T1CONbits.TMR1ON = 1; while (!flags.msec_done); GECE502 Embedded C Programming 15 GECE502 Embedded C Programming 16 4

5 MPLAB C18 Library Functions /******************************* * HiPri_ISR() *******************************/ #pragma interrupt HiPri_ISR void HiPri_ISR() { if (INTCONbits.TMR0IF) Timer0_handler(); else if (PIR1bits.TMR1IF) Timer1_handler(); /******************************* * HiPri_ISR() *******************************/ #pragma interrupt HiPri_ISR void LoPri_ISR(){ MPLAB C18 Library A library is a collection of functions grouped for reference and ease of linking. C18 libraries are included in the lib subdirectory of the installation. C libraries are divided into two groups: processor-independent libraries and processorspecific libraries. Processor-Specific Libraries Files contain definitions that may vary across different members of the PIC18 family. These libraries include all the peripheral routines and the special-function definitions. Processor-Independent Libraries General functions and math functions are in this category. These functions are contained in clib.lib. Refer to MPLAB_C18_Libraries.pdf for a complete list GECE502 Embedded C Programming 17 GECE502 Embedded C Programming memory map FFFFH FFFFH A B C External Data Memory D Code Memory (ROM) E Internal RAM 0000H 0000H GECE502 Embedded C Programming 19 GECE502 Embedded C Programming 20 5

6 code in program memory (ROM) (MOVC) data direct addressable internal data memory (lower 128 bytes), fast access idata indirect addressable internal data memory (entire 256 bytes) xdata external data memory (64 KB) (using DPTR, MOVX) pdata paged external data memory (256 Bytes) MOVX) bdata bit addressable internal data memory (16 bytes, global variables only) far extended RAM and ROM memory spaces (up to 16 MB, needs compiler directive before use, available to certain 8051 variations) code good for: constants and large lookup tables bad for:variables (any kind) data good for: frequently accessed variable requiring fastest access bad for: variable arrays and structures of several bytes idata good for: arrays and structures of limited size but requiring fast access bad for: large data arrays and structures xdata good for: large arrays and structures, and slow or infrequently accessed variables bad for: frequently accessed or fast variable GECE502 Embedded C Programming 21 GECE502 Embedded C Programming 22 pdata good for: medium speed variables and moderatesized arrays and structures bad for: very frequently accessed variables, very large arrays and structures of more than 256 bytes bdata good for: general-purpose bit flags or structure of bit flags bad for: general-purpose variables or arrays or structures Example char data var1; char code text[] = HELLO, ; unsigned long xdata array[100]; float idata x, y, z; unsigned int pdata dimension; unsigned char xdata vector[10][4][4]; char bdata flags; Note /*These declarations are equivalent:*/ data char x; char data x; /*So are these*? data char *x; char *data x; if no memory type specified, in default memory space when running out of stack, in default memory space GECE502 Embedded C Programming 23 GECE502 Embedded C Programming 24 6

7 Specified by using SMALL, COMPACT, LARGE directives SMALL: all variable in internal RAM, fast but restricted COMPACT: all variable in 256B external memory LARGE: all variable in external data memory (64K), slow but large mem space Memory models and default memory space Memory Model Parameters & auto variables Global variables Const Pointer definition SMALL data data data * sfr Special Function Register type sfr name_of_sfr = address_of_sfr; sfr P0 = 0x80; sfr PSW = 0xD0; sfr16 16-bit special function register sfr16 name_of_sfr16 = address_of_sfr16; COMPACT pdata pdata pdata * LARGE xdata xdata xdata * GECE502 Embedded C Programming 25 GECE502 Embedded C Programming 26 sbit bit within a SFR or register in bdata sbit may not be declared inside a function sbit name = SFR_name ^ bit_position; sbit name = SFR_address ^ bit_position; sbit name = sbit_address; sbit name = bdata_variable ^ bit_position; sfr PSW = 0xD0; sbit OV = 0xD0^2; sbit OV = 0xD2; int bdata ibase; sbit OV = PSW^2; sbit mybit15 = ibase^15; bit general purpose bit, in internal RAM (16 B, 128 bits) bit name [= initial_value]; static bit done_flag = 0; bit testfunc (bit flag1, bit flag2) { //bit declaration not allowed... return 0; GECE502 Embedded C Programming 27 7

MPLAB C1X Quick Reference Card

MPLAB C1X Quick Reference Card 34 MPLAB C17 Quick Reference MPLAB C17 Command Switches Command Description /?, /h Display help screen /D[=] Define a macro /FO= Set object file name /FE=