Introduction

The Wi-Fi STA power-saving modes defined in the IEEE 802.11 specification include the following key features:

• Enter doze state when no data is being sent or received.

• enter awake state for receiving AP beacon frame

• Utilizes beacon TIM (Traffic Indication Map) for data management

During the station’s sleep period, it cannot receive any data frames. Therefore, the AP must buffer any pending frames, and the STA must periodically wake up to check for beacon frames.

The Wi-Fi timeline of power-saving mode is illustrated below:

Based on the above standard IEEE 802.11 power saving mechanism, the Ameba SoC provides three Wi-Fi power-saving modes:

Mode	Full name	Description
IPS	Inactive Power Save	Implements a complete power-down state when not connected.
LPS	Legacy Power Save	Switches between awake and doze states under Wi-Fi connection, periodically turns the transceiver on or off for power saving.
WoWLAN	Wake on Wireless LAN	Allows the SoC system to enter Sleep Mode while maintaining Wi-Fi connectivity. The system can be woken up by unicast packets, broadcast/multicast packets (optional), or AP disconnect event.

IPS Mode

The IPS (Inactive Power Save) mode is specifically designed for scenarios where the device is not connected to a Wi-Fi network. It enables the device to enter a sleep state during periods of inactivity, thereby significantly extending battery life.

IPS generally supports two distinct sleep level:

• Wi-Fi Power Off: In this state, the Wi-Fi module is completely powered down to achieve maximum power savings.

• Power Gating (PG) Mode: This state utilizes power gating techniques, which allows for a much faster exit from IPS mode upon wakeup.

Programming Interface

Ameba Wi-Fi controls the IPS behavior using the wifi_set_ips_internal() function and a set of related parameters. The IPS control flow is depicted below:

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Parameter	Type	Value	Description	Default
ips_enable	u8	0/1	Disable/Enable IPS	1
ips_level	u8	RTW_IPS_WIFI_OFF	Wi-Fi power off in IPS	RTW_IPS_WIFI_OFF
		RTW_IPS_WIFI_PG	Wi-Fi power gating in IPS
ips_ctrl_by_usr	u8	0	Enable/Disable IPS via API	0
		1	Enter/Exit IPS mode via API

Refer to the table below for the behavior of each combination:

ips_enable	ips_ctrl_by_usr	wifi_set_ips_internal	Behavior
0	0	Y	Dynamically enables/disables IPS. IPS is disabled by default.
0	1	Y	IPS is disabled.
0	X	N	IPS is disabled.
1	0	Y	Dynamically enables/disables IPS. IPS is enabled by default.
1	1	Y	Dynamically enter/exit IPS mode. Calling wifi_set_ips_inetrnal() allows for a quick exit from IPS mode.
1	X	N	IPS is enabled. System enters the configured power-saving level based on periodic Wi-Fi state monitoring.

LPS Mode

The core idea of LPS (Legacy Power Save) mode is to allow a client station (STA) to enter a low-power sleep state while associated with an Access Point (AP) but with no active data traffic. During this sleep period, the AP buffers any incoming downstream data intended for the STA, thus conserving the STA’s power.

An STA operating in LPS mode must periodically wake up to listen for beacon frames broadcast by the AP. By examining the Traffic Indication Map (TIM) element within these beacons, the STA can determine if the AP has buffered data for it. If the TIM indicates that data is pending, the STA will remain awake to communicate with the AP and retrieve the buffered frames. Otherwise, it can return to sleep until the next scheduled wakeup.

Parameter	Type	Value	Description	Default
lps_enable	u8	0 / 1	Disable/Enable LPS	1
lps_listen_interval	u8	0	Wakes up at each Target Beacon Transmission Time (TBTT) to receive the beacon frame.	0
		> 0	Configure the interval for receiving beacon frames, unit: 102.4ms (TBTT interval)

WoWLAN Mode

WoWLAN (Wake on Wireless LAN) is a system-level power-saving mode where the system enters the Power-Saving Mode—Sleep Mode when idle, while still maintaining the Wi-Fi connection.

In WoWLAN mode, Wi-Fi events can act as a wake-up source to wake up the system:

• Receipt of a targeted unicast packet.

• Receipt of a broadcast or multicast packet.

• An Access Point (AP) disconnection event.

To provide developers with granular control, we offer a configuration option to specify whether incoming broadcast and multicast packets should trigger a system wake-up.

Parameter	Type	Value	Description	Default
wowlan_rx_bcmc_dis	u8	0 / 1	Enable/Disable the ability for broadcast or multicast frames to wake the system in WoWLAN mode.	0