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Serial Interface in CApplication to Magswipe
Lecture Content• In this lecture, we have a broken-up a C-code thatreads magswipe data into its composite chunks• We will go through these chunks, describing theirfunctions and bits of new stuff• Your job will be to put the chunks together and get itall to work• We start with a template of where things go…
Magswipe Handling Program Outline #include^ <various^ things,^ including
conio.h> int^ main(int^ argc,^ char*
argv[]) {//^ type^ definitions//^ open^ serial^ port^ as
COMXX^ (COM1^ if^ built-in)// establish whether 5 or^7 bits^ through^ argv[1],
and^ pick^ mask while^ (!kbhit()){ReadFile(hSerial,^ sInBuff,
1,^ &dwBytesRead,^ NULL); if^ (dwBytesRead^ >^ 0){//^ apply^ masks//^ parity^ check//^ LRC^ calculation//^ string^ formatting}}// print^ resultsCloseHandle(hSerial);return^ 0;}
Serial Port Access in Windows (in 3 pieces) #include^ <fcntl.h>#include^ <errno.h>#include^ <windows.h>//////////////////////////^ Open^ COMXX^ (COM1^ if^
built-in)HANDLE hSerial;hSerial = CreateFile("COMXX",GENERIC_READ^ |^ GENERIC_WRITE,0,0,OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL,0); Windows serial code worked out by Dan Creveling
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if(hSerial==INVALID_HANDLE_VALUE){if(GetLastError()==ERROR_FILE_NOT_FOUND)printf("File^ Not^
Found.\n");elseprintf("Generic Error.\n");exit(-1); } DCB^ dcbSerialParams^ =^ {0};dcbSerialParams.DCBlength=sizeof(dcbSerialParams);if(!GetCommState(hSerial,
&dcbSerialParams)) {printf("Error^ Getting
State.\n");CloseHandle(hSerial);exit(-1); } dcbSerialParams.BaudRate
=^ CBR_9600;
dcbSerialParams.ByteSize
=^ 8;
dcbSerialParams.StopBits
=^ ONESTOPBIT;
dcbSerialParams.Parity^
=^ NOPARITY;
if(!SetCommState(hSerial,
&dcbSerialParams)) {printf("Error^ setting
State.\n");CloseHandle(hSerial);exit(-1); } COMMTIMEOUTS^ timeouts^ =
timeouts.ReadIntervalTimeout
=^ 50;
timeouts.ReadTotalTimeoutConstant
=^ 50;
timeouts.ReadTotalTimeoutMultiplier
=^ 10;
timeouts.WriteTotalTimeoutConstant
=^ 50;
timeouts.WriteTotalTimeoutMultiplier
=^ 10;
if(!SetCommTimeouts(hSerial,
&timeouts)) {printf("Error^ setting
timeouts.\n");CloseHandle(hSerial);exit(-1); } // END^ Open^ COM1////////////////////////
The funky stuff
•^ Lots of weirdness accompanied that last bit– much of it derived from
windows.h • http://source.winehq.org/source/include/windows.h
(included within^ windows.h
•^ http://source.winehq.org/source/include/winbase.h• Typedefs– new variable types may be defined to augment the standard ones– example:^ typdef unsigned char
int8;
-^ now can use:^ int8 my_variable;
in declaration
(included from^ windows.h
DWORD;
BOOL;
BYTE;
Structures
•^ Sometimes want to lump data together undercommon variable– now^ person2.gpa
^ 1.324,^ person2.name[0]
^ ‘M’
- can assign^ person1.student_id = 0498213
, etc.
struct^ {int^ student_id;char^ name[80];char^ major[8];double^ gpa;}^ person1,^ person2={0578829,”Mot– in above, initialized one in declaration, but not both•^ can do anything you want•^ not restricted to two, for that matter
Turphy”,”PHYS”,1.324};
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unsigned^ int^ i,parity;//^ within^ loop…parity^ =^ 0;for^ (i=0;^ i<XX;^ i++){parity^ +=^ (inbyte
^ i)^ &^ 0x01;^ //^
count^ the^ number^ of^ ones
Checking parity for each byte• The magswipe stream should always obey odd parity– odd number of ones in packet– error checking scheme• The following within the byte-processing loop countsthe ones: }
Keeping track of the LRC unsigned short^ LRC=0,LRCflag=1;// within loop…if(LRCflag){LRC ^= inbyte;^ //^ Calculate^ Longitudinal
Redundancy^ Check }if(inbyte^ ==^ 0xXX){LRCflag^ =^ XX;^ //^ Stop
calculating^ LRC^ after^
End^ Sentinel
•^ The Longitudinal Redundancy Check is a final checkon data integrity– in case a two-bit error satisfied parity by accident•^ A common method is XOR– XOR all data within stream, byte-by-byte to arrive at finalLRC }
#include^ <string.h>char^ out_string[80]="",out_char_arr[2]=“x”;char^ parity_string[80]="",par_char_arr[2];char^ charmap5[17]="0123456789:;<=>?";char^ charmap7[65]="^ !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_";//^ within^ loop…if^ (n_bits^ ==^ XX)
out_char_arr[0]^ =^ charmap5[code];if (XX == XX) out_char_arr[XX]^ =^ XX[XX];strcat(out_string,out_char_arr);sprintf(par_char_arr,"%d",XX);^ //
write^ parity^ into^ string XX(parity_string,par_char_arr);
//^ append^ char^
to^ string XX("Got^ inbyte^ %02x;^ code
%2d;^ char^ %s^ with^ parity
=^ %XX\n",
String Formatting inbyte,code,out_char_arr,parity);
Notes on String Formatting• Strings are ugly in C– for out_char_arr[2], initialize as
“x”
-^ effectively the same as: • out_char_arr[0]^ =^ ‘x’ • out_char_arr[1]^ =^ ‘\0’ – drop-in replacement of^ out_char_arr[0]
in program maintains
the necessary^ ‘\0’^ at the end of the string– concatenate entries onto out_string via:^ • strcat(out_string,out_char_arr); – place values into^ par_char_arr[]
via^ sprintf()
- sprintf()^ takes care of the
‘\0’^ automatically
-^ could also say:^ par_char_arr[0]
=^ '0'^ +^ parity;
-^ adds the parity to the character code: relies on ASCII table’s order• The string.h^ library contains a number of usefulmanipulations for strings– but this doesn’t wholly make up for the deficit
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char^ LRCchar;//^ after^ loop^ is^ done…printf("%s\n",out_string);
//^ print
composite^ string printf("%XX\n",parity_string);
//^ print^
parity^ string printf(“LRC^ =^ %d\n”,LRC);if^ (n_bits^ ==^ 5)^ LRCchar
=^ charmap5[LRC^ &^ mask]; if^ (XX^ XX^ XX)^ XX^ =^ XX[XX];
//^ same^ deal^ for
7-bit printf(“LRC^ =^ %c\n”,LRCchar);
Final output^
Putting it together• The program snippets preceding should be enough toget the magswipe working– but for the love of all that is good, please place declarationsand initialization stuff together, not piecewise as in lecture• What comes out looks like: Hit ^ to^ stop^ stream^ and^ exitGot inbyte^ 0b;^ code^ 11;^ char^ ;^ with
parity^ =^3 Got^ inbyte^ 04;^ code^ 4;
char^4 with^ parity^ =^1 Got^ inbyte^ 07;^ code^ 7;
char^7 with^ parity^ =^3 Got^ inbyte^ 01;^ code^ 1;
char^1 with^ parity^ =^1 Got^ inbyte^ 02;^ code^ 2;
char^2 with^ parity^ =^1 :Got^ inbyte^ 10;^ code^ 0;
char^0 with^ parity^ =^1 Got^ inbyte^ 10;^ code^ 0;
char^0 with^ parity^ =^1 Got^ inbyte^ 1f;^ code^ 15;
char^?^ with^ parity^ =^5 Got^ inbyte^ 16;^ code^ 6;
char^6 with^ parity^ =^3 Got^ inbyte^ 00;^ code^ 0;
char^0 with^ parity^ =^0 Got^ inbyte^ 00;^ code^ 0;
char^0 with^ parity^ =^0 : ;4712584314171608=081210130451458800000?600000 3131131131113131131111111311311311111115300000
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