Chapter 4. API Guides
4.10.3 Bluetooth Events
Various modules of the Bluetooth stack deliver events to applications via dedicated callback functions. Callback
functions receive the event type (enumerated value) and event data (union of structures for each event type). The
following list gives the registration API name, event enumeration type, and event parameters type.
• BLE GAP: esp_ble_gap_register_callback(), esp_gap_ble_cb_event_t,
esp_ble_gap_cb_param_t.
• BT GAP: esp_bt_gap_register_callback(), esp_bt_gap_cb_event_t,
esp_bt_gap_cb_param_t.
• GATTC: esp_ble_gattc_register_callback(), esp_bt_gattc_cb_event_t,
esp_bt_gattc_cb_param_t.
• GATTS: esp_ble_gatts_register_callback(), esp_bt_gatts_cb_event_t,
esp_bt_gatts_cb_param_t.
• SPP: esp_spp_register_callback(), esp_spp_cb_event_t, esp_spp_cb_param_t.
• Blufi: esp_blufi_register_callbacks(), esp_blufi_cb_event_t,
esp_blufi_cb_param_t.
• A2DP: esp_a2d_register_callback(), esp_a2d_cb_event_t, esp_a2d_cb_param_t.
• AVRC: esp_avrc_ct_register_callback(), esp_avrc_ct_cb_event_t,
esp_avrc_ct_cb_param_t.
• HFP Client: esp_hf_client_register_callback(), esp_hf_client_cb_event_t,
esp_hf_client_cb_param_t.
• HFP AG: esp_hf_ag_register_callback(), esp_hf_ag_cb_event_t,
esp_hf_ag_cb_param_t.
4.11 Support for external RAM
4.11.1 Introduction
ESP32-S2 has a few hundred kilobytes of internal RAM, residing on the same die as the rest of the chip components.
It can be insufficient for some purposes, so ESP32-S2 has the ability to also use up to 10.5 MB of external SPI RAM
memory. The external memory is incorporated in the memory map and, with certain restrictions, is usable in the
same way as internal data RAM.
4.11.2 Hardware
ESP32-S2 supports SPI PSRAM connected in parallel with the SPI flash chip. While ESP32-S2 is capable of support-
ing several types of RAM chips, ESP-IDF currently only supports Espressif branded PSRAM chips (ESP-PSRAM32,
ESP-PSRAM64, etc).
Note: Some PSRAM chips are 1.8 V devices and some are 3.3 V. The working voltage of the PSRAM chip must
match the working voltage of the flash component. Consult the datasheet for your PSRAM chip and ESP32-S2 device
to find out the working voltages. For a 1.8 V PSRAM chip, make sure to either set the MTDI pin to a high signal level
on bootup, or program ESP32-S2 eFuses to always use the VDD_SIO level of 1.8 V. Not doing this can damage the
PSRAM and/or flash chip.
Note: Espressif produces both modules and system-in-package chips that integrate compatible PSRAM and flash
and are ready to mount on a product PCB. Consult the Espressif website for more information.
For specific details about connecting the SoC or module pins to an external PSRAM chip, consult the SoC or module
datasheet.
Espressif Systems 1332
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