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RE: RedBoot gets() implimentation question
- To: Grant Edwards <grante at visi dot com>
- Subject: RE: [ECOS] RedBoot gets() implimentation question
- From: Gary Thomas <gthomas at cambridge dot redhat dot com>
- Date: Thu, 18 Jan 2001 16:08:52 -0700 (MST)
- Cc: ecos-discuss at sources dot redhat dot com
- Organization: Red Hat, Inc.
On 18-Jan-2001 Grant Edwards wrote:
>
> If you don't mind, I've got a couple questions about the
> implimentation of gets() in RedBoot:
>
> ========================================================================
> gets(char *buf, int buflen, int timeout)
> {
> [...]
>
> while (true) {
>#ifdef CYGSEM_REDBOOT_FLASH_CONFIG
> if (script && *script) {
> c = *script++;
> } else
>#endif
> if ((timeout > 0) && (ptr == buf)) {
> mon_set_read_char_timeout(50);
> while (timeout > 0) {
> res = mon_read_char_with_timeout(&c);
> if (res) {
> // Got a character
> break;
> }
> timeout -= 50;
> }
> if (res == false) {
> return _GETS_TIMEOUT; // Input timed out
> }
> } else {
> mon_read_char(&c);
> }
> *ptr = '\0';
> switch (c) {
> [...]
> ========================================================================
>
> The test ((timeout > 0) && (ptr == buf)) means that the timeout
> only applies for the first character, and once we've received
> that first character we use blocking reads until we see an
> end-of-line?
>
> That means that network polling stops and TCP sockets (and
> associated timers) go dead between between the time the first
> character is received and the newline is received? [I don't
> think that's a problem, but it's something to keep in mind.]
>
Correct. This was a design choice - avoid the overhead of polling
for potential new TCP connections (all that's really going on here)
once data starts coming in.
>
> I'm also curious about the inner loop:
>
> mon_set_read_char_timeout(50);
> while (timeout > 0) {
> res = mon_read_char_with_timeout(&c);
> if (res) {
> // Got a character
> break;
> }
> timeout -= 50;
> }
>
> Would the following be equivalent?
>
> mon_set_read_char_timeout(timeout);
> res = mon_read_char_with_timeout(&c);
>
Yes and no. Yes - the overall timeout would be the same. No since
we want to go back and check for new TCP connections as often as is
reasonable.