AN669 MICROCHIP | Alldatasheet
Document overview
- Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
- PDF pages: 7
Technical content
M Ó 1997 Microchip Technology Inc. DS00669A-page 1 INTRODUCTION With the advent of MPLAB-C, the Microchip C-com- piler, many PICmicro ä users need to embed existing assembly language routines and/or Microchip applica- tion notes into C. This application note explains how to embed an assembly language program into MPLAB-C, version 1.10, and the issues therein. For example, embedding interrupt save and restore must be done using assembly language. Also, critical timing routines may require assembly. The 32-bit floating point multiply routine from AN575 is used to illustrate this process. The remaining 32-bit floating point math routines are embedded into individual C functions and are included in the file accompanying this application note. PROCEDURE For this example, we’ll use a PIC16C74A with 4K Program Memory, and 192 bytes of RAM. Embedding assembly routines In order to embed an assembly language routine in C code place the #asm and #endasm directives around the assembly routine. Furthermore, if this is a subrou- tine, as is the case with the floating point multiply, then embed the assembly code within a C function declara- tion. The #asm construct is illustrated in Example 1 with an excerpt from the 32-bit floating point routine. Authors: Rick Evans Microchip Technology, Inc. Richard Fischer EXAMPLE 1: #ASM, #ENDASM CONSTRUCT void fpm32(void) #asm FPM32 MOVF AEXP,W ;test for zero BTFSS _Z ;arguements MOVF BEXP,W BTFSC _Z GOTO RES032M M32BNE0 MOVF AARGB0,W XORWF BARGB0,W MOVWF SIGN ;save sign MOVF BEXP,W ;in SIGN ADDWF EXP, F MOVLW EXPBIAS-1 ;...etc. #endasm Locating the Routine in Program Memory, GOTO s and CALL s There are two 2K word pages of program memory in the PIC16C74A. Program memory 000h to 7FFh is page 0, 800h to FFFh is page 1. By making fpm32() a C function, MPLAB-C initializes the appropriate page bit in the PCLATH register before the subroutine call is made. (See data sheet for more on PCLATH). A potential problem could arise, however, if the new C function, fpm32(), crosses the page boundary (7FFh,800h). MPLAB-C does not insert code into the assembly code to initialize the page bits (remember MPLAB-C does take care of paging for function calls). That means it is up to the programmer to either; 1) add assembly language to initialize PCLATH appropriately, or 2) move the entire #asm function within a single page. Option 1 involves more work. The programmer must first compile the C code, then analyze the listing file to see if the assembly function crossed a page boundary. Finally, add the appropriate assembly lan- guage to initialize PCLATH then re-compile. This solu- tion is not desirable since every time new C code is added to or deleted from the program, the routine, fpm32() can potentially move across the page bound- ary. Option 2 is the simplest solution - to locate the C function in a single page. Embedding Assembly Routines into C Language Using a Floating Point Routine as an Example AN669
Ó 1997 Microchip Technology Inc. DS00669A -page 2 AN669 To illustrate, lets force fpm32() to cross the page boundary. A pragma directive is required to locate a routine (Example 2). EXAMPLE 2: FOR CING FPM32 TO CR OSS THE PA G E BOUNDAR Y #pragma memory ROM [MAXROM-0x7F0] @ 0x7F0; #include "fpm32.inc" The listing file generated is shown in Example 3. Notice the statement GOTO MTUN32 at address 0x7FC. How- ever, the routine MTUN32 is located at address 0x801. Remember , with the PIC16C74A the GOTO instruction only has an eleven bit address range. With the GOTO MTUN32 example, one more bit of address is needed to branch to 0x801 from 0x7FC. The extra bit of address is located in the PCLATH register. That means assem- bly code would have to be inserted into the floating point routines to initialize PCLATH before each GOTO Since this solution is not desirable, the best approach is to locate the floating point subroutine in a single page. For example, change the pragma directive in Example 2 to locate the routine at 0x800. It is important to note that when fpm32() is called as a C function, the page bit in PCLATH is updated by MPLAB-C . In other words MPLAB-C adds the neces- sary assembly language code needed to call fpm32() or any other C function. The C function is called cor- rectly, but once within the C function, the raw embed- ded assembly language might have GOTO s or CALL s that cross over the page boundar y and cause problems. EXAMPLE 3: FPM32 F OR CED TO AD DRESS 0 x7F0 TO SHO W CR OSSING FR OM PA G E 0 TO PA G E 1 void fpm32 (void) #asm . some code here 07F0 0838 FPM32 MOVF AEXP,W ;test for zero arguments 07F1 1D03 BTFSS _Z 07F2 0839 MOVF BEXP,W 07F3 1903 BTFSC _Z 07F4 284E GOTO RES032M 07F5 0826 M32BNE0 MOVF AARGB0,W 07F6 0633 XORWF BARGB0,W 07F7 00AE MOVWF SIGN ;save sign in SIGN 07F8 0839 MOVF BEXP,W 07F9 07B8 ADDWF EXP, F 07FA 307E MOVLW EXPBIAS-1 07FB 1C03 BTFSS _C 07FC 2801 GOTO MTUN32 ;**** WON’T WORK ! 07FD 02B8 SUBWF EXP,F 07FE 1803 BTFSC _C 07FF 2843 GOTO SETFOV32M ;set multiply overflow flag 0800 2804 GOTO MOK32 0801 02B8 MTUN32 SUBWF EXP,F ;**** IN PAGE 1 ! 0802 1C03 BTFSS _C 0803 2854 GOTO SETFUN32M . some more code here #endasm
Ó 1997 Microchip Technology Inc. DS00669A -page 3 AN669 Assemb ly Language Variables, Include Files, etc. For the floating point math routines of AN575, there is one include file which contains important constant and register declarations: math16.inc . This file of declara- tions is rather extensive, how ever, it is straightforward to convert it to C. Example 4 shows a segment of the math16.inc requiring some attention for the conver- sion. EXAMPLE 4: MATH16.INC E XCERPT FR OM AN575. ASSEMB LY LANGUA G E FILE B0 equ 0 B1 equ 1 B2 equ 2 B3 equ 3 B4 equ 4 B5 equ 5 B6 equ 6 B7 equ 7 MSB equ 7 LSB equ 0 . etc. AARGB7 equ 0x20 AARGB6 equ 0x21 AARGB5 equ 0x22 AARGB4 equ 0x23 AARGB3 equ 0x24 AARGB2 equ 0x25 AARGB1 equ 0x26 AARGB0 equ 0x27 AARG equ 0x27 ; most significant ; byte of argument A These Constant and Variable Declarations Need to be Converted to C Language Dec larations Example 5 shows the equivalent C constant and vari- able declarations. The equates in assembly language create constants. The equivalent C language is a #define . Moreover, variables are declared in assem- bly language by equating a variable name to a register RAM location (i.e. AARGB7 equ 0x20 ). In C the vari- ables are declared by assigning a type to the variable. In the listing in Example 5, AARGB7 is declared as an unsigned integer data type. EXAMPLE 5: THE CON VER TED MATH16C.C FILE . C LANGUA G E FILE #define B0 0 #define B1 1 #define B2 2 #define B3 3 #define B4 4 #define B5 5 #define B6 6 #define B7 7 #define MSB 7 #define LSB 0 . etc. unsigned int AARGB0 @ ACCB0; // most significant byte of argument A unsigned int AARGB1 @ ACCB1; unsigned int AARGB2 @ ACCB2; unsigned int AARGB3 @ ACCB3; unsigned int AARGB4 @ ACCB4; unsigned int AARGB5 @ ACCB5; unsigned int AARGB6 @ ACCB6; unsigned int AARGB7 @ ACCB7; // least significant byte of argument A unsigned int AARG @ ACC; // most significant byte of argument A
Ó 1997 Microchip Technology Inc. USING 32-BIT FLOATING POINT MULTIPL Y Using the 32-bit floating point multiply supplied with AN575 in a C program is straightforward. First, copy the entire routine from the file fpm32.a16 (from AN575). Then, create a function with the same name as the assemb ly routine. Lets take a well known form ula: Let, p = 3.141592654 r = 12.34567898 meters Find A: A pr2= W e need to convert the previous decimal numbers to Microchip 32-bit floating point. Use fpm32 (from AN575), to solve the equation. W e will use MPLAB-C and use our C function named fpm32(). The main routine is listed in Example 6. AN575 comes with a handy utility called fprep.exe This Microchip file is a DOS executable. When running fprep , you can enter in a decimal number and it dis- plays the hexadecimal floating point number. Table 1 shows the numbers in our example and their equivalent floating point formats. TAB LE 1: PICmicro ä 32-BIT FLOATING POINT REPRESENTATIONS OF OUR E XAMPLE EXAMPLE 6: MAIN R OUTINE TO TEST OUT OUR NE W 32-BIT FLOAT MULTIPL Y IN C #include "16c74a.h" #include "math16c.c" #include "fpm32.inc" // Notice that fpm32 is located in page 0 // Thus, all GOTOs reside in the same page. void main (void) AEXP = 0X80; // PI = 3.141592654 AARGB0 = 0X49; AARGB1 = 0X0F; AARGB2 = 0XDB; BEXP = 0X82; // r = 12.34567898 BARGB0 = 0X45; BARGB1 = 0X87; BARGB2 = 0XE7; fpm32(); // AARG = PI * r // you must reload r into BARG since // fpm32() destroys BARG. BEXP = 0X82; // r = 12.34567898 BARGB0 = 0X45; BARGB1 = 0X87; BARGB2 = 0XE7; fpm32(); // AARG = (PI*r)*r while(1); Microchip Floating Point Equivalent Decimal Number EXP B0 (MSB) B1 B2 (LSB) p = 3.141592654 0x80 0x49 0x0F 0xDB r = 12.34567898 meters 0x82 0x45 0x87 0xE7 A = 478.8283246 m -- fprep.exe calculated result 0x87 0x6F 0x6A 0x07 A = 478.8283246 m -- PIC16C74A measured result using MPLAB 3.12 and PICMASTER 16J probe 0x87 0x6F 0x6A 0x07
Ó 1997 Microchip Technology Inc. DS00669A -page 5 AN669 SUMMAR Y For this discussion only the 32-bit floating point multiply is used. How ever, the same principles of embedded assemb ly language routines into C code can be used with other assembly language routines. A summary list of a step- by- step process to embed assembly code into your C code is below:
- Con vert assembly register EQU equates to C vari- able types such as unsigned int.
- Con vert constants to #define in C.
- Place the assembly code into a subroutine using #asm and #endasm
- To avoid paging issues in parts with multiple pro- gram memor y pages, force the code to an address where it will not cross a page boundary. For example: #pragma memory ROM [MAXROM-0x800] @ 0x800;
- Macros and conditional assembly will have to be rewritten in actual in-line assembly code. The MPLAB-C compiler does not support these higher level assembly options to the same degree as the assemb ler, MPASM. For your convenience, all the 32-bit floating point rou- tines in application note AN575 are provided in a zip file along with this application note. Each routine has been separated to work as a stand-alone routine. There is a separate file for each floating point routine. The files ma y be included individually into your C code. Table 2 shows a list of all the files and routines included with this application note. TAB LE 2: 32-BIT FLOATING POINT C FILES/FUNCTIONS INCLUDED WITH THIS APPLICATION NOTE AN575 Original Assemb ly Routine/file * Equivalent C file/function Purpose - example.c The example main() routine calculating the area given the radius. (uses fpm32) FLO2432 flo2432.inc 24-bit integer to 32-bit floating point conversion FLO3232 flo3232.inc 32-bit integer to 32-bit floating point conversion FPD32 fpd32.inc 32-bit floating point divide FPM32 fpm32.inc 32-bit floating point multiply FPA32 FPS32 fpsa32.inc fps32() 32-bit subtract fpa32() 32-bit add 32-bit floating point add 32-bit floating point subtract INT3224 int3224.inc 32-bit floating point to 24-bit integer conversion INT3232 int3232.inc 32-bit floating point to 32-bit integer conversion NRM3232 nrm3232.inc 32-bit normalization of unnormalized 32-bit floating point numbers NRM4032 nrm4032.inc 32-bit normalization of unnormalized 40-bit floating point numbers math16.inc math16c.c variables and constants need for the floating point functions * Check Microchip web site and bulletin board for latest code.
2002 Microchip Technology Inc. Information contained in this publication regarding device applications and the like is intended through suggestion only and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. No representation or warranty is given and no liability is assumed by Microchip Technology Incorporated with respect to the accuracy or use of such information, or infringement of patents or other intellectual property rights arising from such use or otherwise. Use of Microchip’s products as critical com- ponents in life support systems is not authorized except with express written approval by Microchip. No licenses are con- veyed, implicitly or otherwise, under any intellectual property rights. Trademarks The Microchip name and logo, the Microchip logo, FilterLab, KEELOQ, microID, MPLAB, PIC, PICmicro, PICMASTER, PICSTART, PRO MATE, SEEVAL and The Embedded Control Solutions Company are registered trademarks of Microchip Tech- nology Incorporated in the U.S.A. and other countries. dsPIC, ECONOMONITOR, FanSense, FlexROM, fuzzyLAB, In-Circuit Serial Programming, ICSP, ICEPIC, microPort, Migratable Memory, MPASM, MPLIB, MPLINK, MPSIM, MXDEV, PICC, PICDEM, PICDEM.net, rfPIC, Select Mode and Total Endurance are trademarks of Microchip Technology Incorporated in the U.S.A. Serialized Quick Turn Programming (SQTP) is a service mark of Microchip Technology Incorporated in the U.S.A. All other trademarks mentioned herein are property of their respective companies. © 2002, Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved. Printed on recycled paper. Microchip received QS-9000 quality system certification for its worldwide headquarters, design and wafer fabrication facilities in Chandler and Tempe, Arizona in July 1999. The Company’s quality system processes and procedures are QS-9000 compliant for its PICmicro® 8-bit MCUs, KEELOQ® code hopping devices, Serial EEPROMs and microperipheral products. In addition, Microchip’s quality system for the design and manufacture of development systems is ISO 9001 certified. Note the following details of the code protection feature on PICmicro ® MCUs. The PICmicro family meets the specifications contained in the Microchip Data Sheet. Microchip believes that its family of PICmicro microcontrollers is one of the most secure products of its kind on the market today, when used in the intended manner and under normal conditions. There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our knowl - edge, require using the PICmicro microcontroller in a manner outside the operating specifications contained in the data sheet. The person doing so may be engaged in theft of intellectual property. Microchip is willing to work with the customer who is concerned about the integrity of their code. Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not mean that we are guaranteeing the product as “unbreakable”. Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our product. If you have any further questions about this matter, please contact the local sales office nearest to you.
2002 Microchip Technology Inc. M AMERICAS Corporate Office 2355 West Chandler Blvd. Chandler, AZ 85224-6199 Tel: 480-792-7200 Fax: 480-792-7277 Technical Support: 480-792-7627 Web Address: http://www.microchip.com Rocky Mountain 2355 West Chandler Blvd. Chandler, AZ 85224-6199 Tel: 480-792-7966 Fax: 480-792-7456 Atlanta
500 Sugar Mill Road, Suite 200B
Atlanta, GA 30350 Tel: 770-640-0034 Fax: 770-640-0307 Boston
2 Lan Drive, Suite 120
Westford, MA 01886 Tel: 978-692-3848 Fax: 978-692-3821 Chicago
333 Pierce Road, Suite 180
Itasca, IL 60143 Tel: 630-285-0071 Fax: 630-285-0075 Dallas
4570 Westgrove Drive, Suite 160
Addison, TX 75001 Tel: 972-818-7423 Fax: 972-818-2924 Detroit Tri-Atria Office Building
32255 Northwestern Highway, Suite 190
Farmington Hills, MI 48334 Tel: 248-538-2250 Fax: 248-538-2260 Kokomo 2767 S. Albright Road Kokomo, Indiana 46902 Tel: 765-864-8360 Fax: 765-864-8387 Los Angeles
18201 Von Karman, Suite 1090
Irvine, CA 92612 Tel: 949-263-1888 Fax: 949-263-1338 New York
150 Motor Parkway, Suite 202
Hauppauge, NY 11788 Tel: 631-273-5305 Fax: 631-273-5335 San Jose Microchip Technology Inc.
2107 North First Street, Suite 590
San Jose, CA 95131 Tel: 408-436-7950 Fax: 408-436-7955 Toronto
6285 Northam Drive, Suite 108
Mississauga, Ontario L4V 1X5, Canada Tel: 905-673-0699 Fax: 905-673-6509 ASIA/PACIFIC Australia Microchip Technology Australia Pty Ltd Suite 22, 41 Rawson Street Epping 2121, NSW Australia Tel: 61-2-9868-6733 Fax: 61-2-9868-6755 China - Beijing Microchip Technology Consulting (Shanghai) Co., Ltd., Beijing Liaison Office Unit 915 Bei Hai Wan Tai Bldg. No. 6 Chaoyangmen Beidajie Beijing, 100027, No. China Tel: 86-10-85282100 Fax: 86-10-85282104 China - Chengdu Microchip Technology Consulting (Shanghai) Co., Ltd., Chengdu Liaison Office Rm. 2401, 24th Floor, Ming Xing Financial Tower No. 88 TIDU Street Chengdu 610016, China Tel: 86-28-6766200 Fax: 86-28-6766599 China - Fuzhou Microchip Technology Consulting (Shanghai) Co., Ltd., Fuzhou Liaison Office Unit 28F, World Trade Plaza No. 71 Wusi Road Fuzhou 350001, China Tel: 86-591-7503506 Fax: 86-591-7503521 China - Shanghai Microchip Technology Consulting (Shanghai) Co., Ltd. Room 701, Bldg. B Far East International Plaza No. 317 Xian Xia Road Shanghai, 200051 Tel: 86-21-6275-5700 Fax: 86-21-6275-5060 China - Shenzhen Microchip Technology Consulting (Shanghai) Co., Ltd., Shenzhen Liaison Office Rm. 1315, 13/F, Shenzhen Kerry Centre, Renminnan Lu Shenzhen 518001, China Tel: 86-755-2350361 Fax: 86-755-2366086 Hong Kong Microchip Technology Hongkong Ltd. Unit 901-6, Tower 2, Metroplaza
223 Hing Fong Road
Kwai Fong, N.T., Hong Kong Tel: 852-2401-1200 Fax: 852-2401-3431 India Microchip Technology Inc. India Liaison Office Divyasree Chambers
1 Floor, Wing A (A3/A4)
No. 11, O’Shaugnessey Road Bangalore, 560 025, India Tel: 91-80-2290061 Fax: 91-80-2290062 Japan Microchip Technology Japan K.K. Benex S-1 6F 3-18-20, Shinyokohama Kohoku-Ku, Yokohama-shi Kanagawa, 222-0033, Japan Tel: 81-45-471- 6166 Fax: 81-45-471-6122 Korea Microchip Technology Korea 168-1, Youngbo Bldg. 3 Floor Samsung-Dong, Kangnam-Ku Seoul, Korea 135-882 Tel: 82-2-554-7200 Fax: 82-2-558-5934 Singapore Microchip Technology Singapore Pte Ltd.
200 Middle Road
#07-02 Prime Centre Singapore, 188980 Tel: 65-334-8870 Fax: 65-334-8850 Taiwan Microchip Technology Taiwan 11F-3, No. 207 Tung Hua North Road Taipei, 105, Taiwan Tel: 886-2-2717-7175 Fax: 886-2-2545-0139 EUROPE Denmark Microchip Technology Nordic ApS Regus Business Centre Lautrup hoj 1-3 Ballerup DK-2750 Denmark Tel: 45 4420 9895 Fax: 45 4420 9910 France Microchip Technology SARL Parc d’Activite du Moulin de Massy
43 Rue du Saule Trapu
91300 Massy, France
D-81739 Munich, Germany Tel: 49-89-627-144 0 Fax: 49-89-627-144-44 Italy Microchip Technology SRL Centro Direzionale Colleoni Palazzo Taurus 1 V. Le Colleoni 1
20041 Agrate Brianza
Milan, Italy Tel: 39-039-65791-1 Fax: 39-039-6899883 United Kingdom Arizona Microchip Technology Ltd.
505 Eskdale Road
Berkshire, England RG41 5TU Tel: 44 118 921 5869 Fax: 44-118 921-5820 01/18/02 WORLDWIDE SALES AND SERVICE