Re: [PATCH rtw-next v6 2/2] wifi: rtw88: support channel switch in AP mode

[Mehmet Fide]

Hi Ping-Ke,

On 2026-10-19, Ping-Ke Shih wrote:
> If you download beacon to firmware twice within a period of beacon_int,
> a countdown in the air will not present, no? Like this
[...]
> The 4 is missing.

Yes, when a download runs late past the next TBTT. The absolute due
time keeps the pace, one download per beacon interval on average, so
the AP switches when its stations expect it; v5 queued relative to
the previous download and drifted 10 ms per beacon on USB. The price
of a download that late is one stale beacon and one count never sent.
A station takes its switch time from the counts it sees; at worst one
whose first count is the stale one switches one interval late.

Forced on an RTL8821CU with a 90 ms delay on every second download: a
sniffer saw 9, 8, 8, 6, 4, 4, 2, 2 for count 10, the AP finished on
time, and a Windows station followed ten such switches (counts 10 and
50) without a re-association. Without the delay it happened once in
nine switches.

If you would rather not have it: timing the downloads from the TSF,
10 ms after each TBTT, leaves nearly a whole interval before a beacon
goes out without the download. I tried that briefly on the 8821CU;
with a 60 ms delay every count stays on the air. Which do you prefer?

Thanks,
Mehmet