Chapter 4. API Guides
Scenario Description
No WiFi connection In this scenario, no Wi-Fi connection is set up, so
there are no side-effects on the Wi-Fi driver. If
en_sys_seq==true, the Wi-Fi driver is responsible for
the sequence control. If en_sys_seq==false, the appli-
cation needs to ensure that the buffer has the correct
sequence.
Theoretically, the MAC address can be any address.
However, this may impact other stations/APs with the
same MAC/BSSID.
Side-effect example#1 The application calls
esp_wifi_80211_tx to send a beacon with BSSID
== mac_x in AP mode, but the mac_x is not the MAC
of the AP interface. Moreover, there is another AP, say
“other-AP”, whose bssid is mac_x. If this happens,
an “unexpected behavior”may occur, because the
stations which connect to the “other-AP”cannot
figure out whether the beacon is from the “other-AP”
or the esp_wifi_80211_tx.
To avoid the above-mentioned side-effects, we recom-
mend that:
• If esp_wifi_80211_tx is called in Station mode,
the first MAC should be a multicast MAC or the
exact target-device’s MAC, while the second
MAC should be that of the station interface.
• If esp_wifi_80211_tx is called in AP mode, the
first MAC should be a multicast MAC or the
exact target-device’s MAC, while the second
MAC should be that of the AP interface.
The recommendations above are only for avoiding side-
effects and can be ignored when there are good reasons
for doing this.
Have WiFi connection When the Wi-Fi connection is already set up, and the
sequence is controlled by the application, the latter may
impact the sequence control of the Wi-Fi connection, as
a whole. So, the en_sys_seq need to be true, otherwise
ESP_ERR_WIFI_ARG is returned.
The MAC-address recommendations in the“No WiFi
connection”scenario also apply to this scenario.
If the WiFi mode is station mode and the MAC ad-
dress1 is the MAC of AP to which the station is con-
nected, the MAC address2 is the MAC of station inter-
face, we say the packets is from the station to AP. On
the other hand, if the WiFi mode is AP mode and the
MAC address1 is the MAC of the station who connects
to this AP, the MAC address2 is the MAC of AP in-
terface, we say the packet is from the AP to station. To
avoid conflicting with WiFi connections, the following
checks are applied:
• If the packet type is data and is from the station
to AP, the ToDS bit in IEEE 80211 frame con-
trol should be 1, the FromDS bit should be 0,
otherwise the packet will be discarded by WiFi
driver.
• If the packet type is data and is from the AP to
station, the ToDS bit in IEEE 80211 frame con-
trol should be 0, the FromDS bit should be 1,
otherwise the packet will be discarded by WiFi
driver.
• If the packet is from station to AP or from AP
to station, the Power Management, More Data,
Re-Transmission bits should be 0, otherwise the
packet will be discarded by WiFi driver.
ESP_ERR_WIFI_ARG is returned if any check fails.
Espressif Systems 1542
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