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ktallevi
Joined: 17 Dec 2005
Posts: 58
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| timed fgets using Timer |
 Posted: Wed Aug 30, 2006 10:01 am |
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Hi,
Im using a pic18f1320 @ 4Mhz. Ive seen timed_getc functions but Id like to use a timer overflow to cause a timeout when using gets. Basically before calling gets, enable the timer, call gets, then when the timer overflows it can call a different part of the program.
How would I go about this, lets say for a 5 second timeout. Im not sure of the calculation.
thanks |
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rwyoung
Joined: 12 Nov 2003
Posts: 563
Location: Lawrence, KS USA
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| Posted: Wed Aug 30, 2006 1:03 pm |
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Roughly it would be something like this:
| Code: |
timeoutflag = 0;
// configure and enable timer here
// includes setting up of timer values, turning on timer
// and enabling timer's ISR
while(!timeoutflag && !kbhit());
// consider adding restart_wdt() to while loop
if(kbhit())
returnval = getch();
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Then, in the timer's ISR you set timeoutflag = 1
This version will run a little bit LONGER than the value you program into the timer since there is some delay getting into and out of the ISR and you have an extra call to kbhit() to make the decision as to why the code left the while loop.
_________________
Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month! |
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Ttelmah
Guest
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| Posted: Wed Aug 30, 2006 2:47 pm |
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First, I'd say 'abandon gets'. There is nothing 'special' about the internal functions (except they are there already), and gets, is a terrifyingly dangerous function on the PIC. Because it has no 'size' limit, and will carry on accepting characters until it sees the linefeed, if this one character gets omitted, or is corrupted, it can destroy all the RAM contents. There is a much 'better' I/O function, in the 'input.c' library, and a lot of the problems with some code, would disappear if this was substituted. However even this is not 'special', so the answer is to re-code this to add a time delay. If you don't use gets, then the code is not included in your program, so nothing is lost.
Something like:
| Code: |
int16 tick;
int1 exit;
#int_timer2
void tick_interrupt(void) {
if (tick) --tick;
else exit=TRUE;
}
void get_string(char* s, int max, int16 msec) {
int len;
char c;
tick=msec/20;
timeout=false;
setup_timer_2(T2_DIV_BY_16,124,10);
set_timer2(0);
clear_interrupts(INT_TIMER2);
enable_interrupts(INT_TIMER2;
--max;
len=0;
do {
if (kbhit) {
c=getc();
if(c==8) { // Backspace
if(len>0) {
len--;
putc(c);
putc(' ');
putc(c);
}
}
else if ((c>=' ')&&(c<='~'))
if(len<max) {
s[len++]=c;
putc(c);
}
if (c==13) exit=TRUE;
//exit if string is complete
}
} while (!exit)
disable_interrupts(INT_TIMER2);
s[len]=0;
}
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Then just call this with the address of the memory location to be used to hold the string, the maximum number of characters to wait for, and the the to wait (in mSec). The 'wait' has a 20mSec granularity.
Best Wishes |
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souravkumarkar
Joined: 31 Dec 2011
Posts: 5
Location: Baripada
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| How to use this code |
| Posted: Thu Nov 01, 2012 10:11 am |
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| Sir how to use this code in simple. |
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