FIX: support rstamps from the future too.

 * Extend a 32 bit TSF to nearest 64 bit TSF value.
 * When the adapter is a STATION, its local TSF is periodically modified by
 * the hardware to match the BSS TSF (as received in beacon packets), and
 * rstamp may appear to be from the future or from the past (with reference
 * to the current local TSF) because of jitter. This is mostly noticable in
 * highly congested channels. The code uses signed modulo arithmetic to
 * handle both past/future cases and signed-extension to avoid branches.
 * Test cases:
 * extend(0x0000001200000004, 0x00000006) == 0x0000001200000006
 * extend(0x0000001200000004, 0x00000002) == 0x0000001200000002
 * extend(0x0000001200000004, 0xfffffffe) == 0x00000011fffffffe  ! tsfhigh--
 * extend(0x00000012fffffffc, 0xfffffffe) == 0x00000012fffffffe
 * extend(0x00000012fffffffc, 0xfffffffa) == 0x00000012fffffffa
 * extend(0x00000012fffffffc, 0x00000002) == 0x0000001300000002  ! tsfhigh++

diff --git a/target_firmware/wlan/if_ath.c b/target_firmware/wlan/if_ath.c
index 206b5c0e2c674d0a417f7db530791b130b19b2bb..78a02e1a3bb2a1652ea2f02f49f9d2008ea36ac8 100755 (executable)
--- a/target_firmware/wlan/if_ath.c
+++ b/target_firmware/wlan/if_ath.c
@@ -82,19 +82,34 @@ void ath_tgt_tx_sched_normal(struct ath_softc_tgt *sc, struct ath_buf *bf);
 void ath_tgt_tx_sched_nonaggr(struct ath_softc_tgt *sc,struct ath_buf * bf_host);
 
 /*
- * Extend a 32 bit TSF to 64 bit, taking wrapping into account.
+ * Extend a 32 bit TSF to nearest 64 bit TSF value.
+ * When the adapter is a STATION, its local TSF is periodically modified by
+ * the hardware to match the BSS TSF (as received in beacon packets), and
+ * rstamp may appear to be from the future or from the past (with reference
+ * to the current local TSF) because of jitter. This is mostly noticable in
+ * highly congested channels. The code uses signed modulo arithmetic to
+ * handle both past/future cases and signed-extension to avoid branches.
+ * Test cases:
+ * extend(0x0000001200000004, 0x00000006) == 0x0000001200000006
+ * extend(0x0000001200000004, 0x00000002) == 0x0000001200000002
+ * extend(0x0000001200000004, 0xfffffffe) == 0x00000011fffffffe  ! tsfhigh--
+ * extend(0x00000012fffffffc, 0xfffffffe) == 0x00000012fffffffe
+ * extend(0x00000012fffffffc, 0xfffffffa) == 0x00000012fffffffa
+ * extend(0x00000012fffffffc, 0x00000002) == 0x0000001300000002  ! tsfhigh++
  */
 static u_int64_t ath_extend_tsf(struct ath_softc_tgt *sc, u_int32_t rstamp)
 {
        struct ath_hal *ah = sc->sc_ah;
        u_int64_t tsf;
+       a_int32_t tsf_low;
+       a_int64_t tsf_delta;  /* signed int64 */
 
        tsf = ah->ah_getTsf64(ah);
+       tsf_low = tsf & 0xffffffff;
 
-       if (rstamp > (tsf & 0xffffffffULL))
-               tsf -= 0x100000000ULL;
+       tsf_delta = (a_int32_t)rstamp - (a_int64_t)tsf_low;
 
-       return ((tsf & ~0xffffffffULL) | rstamp);
+       return (tsf + (u_int64_t)tsf_delta);
 }
 
 static a_int32_t ath_rate_setup(struct ath_softc_tgt *sc, a_uint32_t mode)