kernel::radio

Which radios this build uses, and whether the board has them.

The feature set

Feature	Means
radio-wifi	Wi-Fi. Costs no static DRAM
radio-bt	The Bluetooth controller is on, in some mode. Reserves DRAM
radio-ble	BLE. Implies radio-bt
radio-bt-classic	BR/EDR. Implies radio-bt

radio-bt is not meant to be selected directly — radio-ble and radio-bt-classic turn it on. It exists as a separate feature because the thing that costs memory is the controller being enabled, not which mode it runs in:

config BTDM_RESERVE_DRAM
    hex
    default 0xdb5c if BT_ENABLED
    default 0

Identical for BLE-only, BR/EDR-only and dual-mode. Keying the memory map on radio-ble would have meant rewriting the linker script the day BR/EDR appeared, for no change in the number.

Enabling both modes is legal and is how dual-mode is selected. It reserves no more DRAM than either alone, but it does forfeit the claw-back described below.

What is not here

BLE Mesh is not a build flag at this layer. It is a host stack above BLE, not a controller mode, so it costs heap rather than static DRAM and would arrive as a crate on top of radio-ble. doc/plan-radio.md lists it as a non-goal for now regardless.

The claw-back

A BLE-only build can hand the unused BR/EDR sections back at runtime — esp_bt_controller_mem_release(ESP_BT_MODE_CLASSIC_BT), which esp-idf documents as releasing “the BSS, data and other sections of the controller to heap. The total size is about 70k bytes.” It is irreversible, which is fine when the mode is fixed at build time. [RELEASE_CLASSIC_MEMORY] says whether this build may do it.

Constants

BLE

const BLE: bool;

BLE specifically.

BT

const BT: bool;

The Bluetooth controller is enabled in some mode. This is the flag the memory map is keyed on — see tools/build/src/map.rs.

BT_CLASSIC

const BT_CLASSIC: bool;

BR/EDR (“Bluetooth Classic”) specifically.

RELEASE_CLASSIC_MEMORY

const RELEASE_CLASSIC_MEMORY: bool;

Whether the BR/EDR sections may be released to the heap at init.

Only when Bluetooth is on and Classic is not wanted. Releasing while Classic is in use would free memory the controller is about to rely on, and the operation cannot be undone.

WIFI

const WIFI: bool;

Wi-Fi is in use.