Working with the Unix OS

I/O Subsystem
Raw Mode
Raw mode is important for screen
oriented applications.
Figure 39. Raw Mode - Reading 5 character
Bursts
#include
#include
struct termio savetty;
main()
{
extern void sigcatch();
struct termio newtty;
int nrd;
char buf[32];
signal(SIGINT, sigcatch);
if (ioctl(0, TCGETA, &savetty) == -1)
{
printf("ioctl failed: not a tty\n");
exit(0);
}
newtty = savetty;
newtty.c_lflag &= ~ICANON; /* turn off canonical mode */
newtty.c_lflag &= ~ECHO;
/* turn off character echo */
newtty.c_cc[VMIN] = 5; /* minimum 5 chars */
newtty.c_cc[VTIME] = 100; /* 10 see interval */
if (ioctl(0, TCSETAF, &newtty) == -1)
{
printf("cannot put tty into raw mode\n");
exit(0);
}
for (;;)
{
nrd = read(0, buf, sizeof(buf));
buf[nrd] = 0;
printf("read %d chars '%s'\n", nrd, bur);
}
}
void sigcatch();
{
ioctl(0, TCSETAF, &savetty);
exit(0);
}
#include
main()
{
register int i, n; int fd;
char buf[256];
/* open terminal read-only with no-delay option */
if ((fd=open("/dev/tty", O_RDONLY | O_NDELAY)) == -1)
exit(0);
n = 1;
for (;;) /* for ever */
{
for (i = 0; i < n; i++)
;
if (read (fd, bur, sizeof(buf)) > 0)
{
printf("read at n %d\n", n);
n--;
}
else /* no data read; returns due to no-delay */
n++;
}
}
Polling
- Can "poll" terminals by opening with nodelay,
etc. but processing intensive.
- BSD system has a select system call
select (nfds, rfds, wfds, efds,
timeout)
nfds = number of file descriptors
rfds, wfds, efds = bit masks (read,
write, exceptions)
timeout = how long to wait
Figure 40. Polling a Terminal
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