[src/trunk]: src/sys/net80211 Simplify the duration calculations somewhat.

[mycroft <mycroft%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/8edc6a1f7e18
branches:  trunk
changeset: 572240:8edc6a1f7e18
user:      mycroft <mycroft%NetBSD.org@localhost>
date:      Mon Dec 27 05:35:33 2004 +0000

description:
Simplify the duration calculations somewhat.
* Add an intermediate variable, ctsrate, which is currently derived directly
 from rate, but may be handled differently later (especially for 11g).
* Assume ACKs are sent at the same rate as the original data packet, as ath
  does, shortening the ACK reservation time substantially.
* Add a note that we need to deal with not adding the ACK time for some
  packets, though this is not implemented yet.

Questions:
* How do we affect the control rate used to send RTS/CTS packets?
* Is the PLCP header length actually controlled by the preamble length
  selection, or should this be based on the transmit rate?

Of course short preamble is not actually implemented/working yet.

diffstat:

 sys/net80211/ieee80211_output.c |  55 ++++++++++++++++++----------------------
 1 files changed, 25 insertions(+), 30 deletions(-)

diffs (108 lines):

diff -r 8e71813c18b2 -r 8edc6a1f7e18 sys/net80211/ieee80211_output.c
--- a/sys/net80211/ieee80211_output.c   Mon Dec 27 02:46:22 2004 +0000
+++ b/sys/net80211/ieee80211_output.c   Mon Dec 27 05:35:33 2004 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: ieee80211_output.c,v 1.21 2004/12/27 01:57:58 mycroft Exp $    */
+/*     $NetBSD: ieee80211_output.c,v 1.22 2004/12/27 05:35:33 mycroft Exp $    */
 /*-
  * Copyright (c) 2001 Atsushi Onoe
  * Copyright (c) 2002, 2003 Sam Leffler, Errno Consulting
@@ -35,7 +35,7 @@
 #ifdef __FreeBSD__
 __FBSDID("$FreeBSD: src/sys/net80211/ieee80211_output.c,v 1.10 2004/04/02 23:25:39 sam Exp $");
 #else
-__KERNEL_RCSID(0, "$NetBSD: ieee80211_output.c,v 1.21 2004/12/27 01:57:58 mycroft Exp $");
+__KERNEL_RCSID(0, "$NetBSD: ieee80211_output.c,v 1.22 2004/12/27 05:35:33 mycroft Exp $");
 #endif
 
 #include "opt_inet.h"
@@ -296,40 +296,46 @@
 ieee80211_compute_duration1(int len, uint32_t flags, int rate,
     struct ieee80211_duration *d)
 {
-       int ack, bitlen, cts, data_dur, remainder;
+       int pre, ctsrate;
+       int bitlen, data_dur, remainder;
 
        /* RTS reserves medium for SIFS | CTS | SIFS | (DATA) | SIFS | ACK
         * DATA reserves medium for SIFS | ACK
+        *
+        * XXXMYC: no ACK on multicast/broadcast or control packets
         */
 
        bitlen = len * 8;
 
+       pre = IEEE80211_DUR_DS_SIFS;
+       if ((flags & IEEE80211_F_SHPREAMBLE) != 0)
+               pre += IEEE80211_DUR_DS_SHORT_PREAMBLE + IEEE80211_DUR_DS_FAST_PLCPHDR;
+       else
+               pre += IEEE80211_DUR_DS_LONG_PREAMBLE + IEEE80211_DUR_DS_SLOW_PLCPHDR;
+
 #if 0
        /* RTS is always sent at 1 Mb/s.  (XXX Really?) */
        d->d_rts_plcp_len = sizeof(struct ieee80211_frame_rts) * 8;
 #endif
        d->d_residue = 0;
        data_dur = (bitlen * 2) / rate;
+       remainder = (bitlen * 2) % rate;
+       if (remainder != 0) {
+               d->d_residue = (rate - remainder) / 16;
+               data_dur++;
+       }
 
        switch (rate) {
        case 2:         /* 1 Mb/s */
        case 4:         /* 2 Mb/s */
                /* 1 - 2 Mb/s WLAN: send ACK/CTS at 1 Mb/s */
-               cts = IEEE80211_DUR_DS_SLOW_CTS;
-               ack = IEEE80211_DUR_DS_SLOW_ACK;
+               ctsrate = 2;
                break;
        case 11:        /* 5.5 Mb/s */
        case 22:        /* 11  Mb/s */
        case 44:        /* 22  Mb/s */
-               remainder = (bitlen * 2) % rate;
-               if (remainder != 0) {
-                       data_dur++;
-                       d->d_residue = (rate - remainder) / 16;
-               }
-
                /* 5.5 - 11 Mb/s WLAN: send ACK/CTS at 2 Mb/s */
-               cts = IEEE80211_DUR_DS_FAST_CTS;
-               ack = IEEE80211_DUR_DS_FAST_ACK;
+               ctsrate = 4;
                break;
        default:
                /* TBD */
@@ -338,25 +344,14 @@
 
        d->d_plcp_len = data_dur;
 
-       d->d_rts_dur = data_dur + 3 * (IEEE80211_DUR_DS_SIFS +
-           IEEE80211_DUR_DS_SHORT_PREAMBLE +
-           IEEE80211_DUR_DS_FAST_PLCPHDR) + cts + ack;
+       d->d_rts_dur =
+           pre + (IEEE80211_DUR_DS_SLOW_CTS * 2) / ctsrate +
+           pre + data_dur +
+           pre + (IEEE80211_DUR_DS_SLOW_ACK * 2) / ctsrate;
 
-       /* Note that this is the amount of time reserved *after*
-        * the packet is transmitted: just long enough for a SIFS
-        * and an ACK.
-        */
-       d->d_data_dur = IEEE80211_DUR_DS_SIFS +
-           IEEE80211_DUR_DS_SHORT_PREAMBLE + IEEE80211_DUR_DS_FAST_PLCPHDR +
-           ack;
+       d->d_data_dur =
+           pre + (IEEE80211_DUR_DS_SLOW_ACK * 2) / rate;
 
-       if ((flags & IEEE80211_F_SHPREAMBLE) != 0)
-               return 0;
-
-       d->d_rts_dur += 3 * IEEE80211_DUR_DS_PREAMBLE_DIFFERENCE +
-                       3 * IEEE80211_DUR_DS_PLCPHDR_DIFFERENCE;
-       d->d_data_dur += IEEE80211_DUR_DS_PREAMBLE_DIFFERENCE +
-                        IEEE80211_DUR_DS_PLCPHDR_DIFFERENCE;
        return 0;
 }