ESP-Hosted-FG

Index

1. Introduction
2. Hardware and Software setup
- Setup With Linux Host
- Setup With MCU host
3. Control Path
- Control Path APIs
- Demo Apps
4. Design
5. Throughput performance

1. Introduction

This version of ESP-Hosted provides:

A standard 802.3 network interface for transmitting and receiving 802.3 frames
A standard HCI interface over which Bluetooth/BLE is supported
A control interface to configure and control Wi-Fi on ESP board

ESP-Hosted-FG solution makes use of host's existing TCP/IP and/or Bluetooth/BLE software stack and hardware peripheral like SPI/SDIO/UART to connect to ESP firmware with very thin layer of software.

Although the project doesn't provide a standard 802.11 interface to the host, it provides a easy way, i.e. control path, to configure Wi-Fi. For the control path between the host and ESP board, ESP-Hosted-FG makes use of Protobuf, which is a language independent data serialization mechanism.

1.1 Connectivity Features

ESP-Hosted-FG solution provides following WLAN and BT/BLE features to the host:

WLAN Features:
- 802.11b/g/n
- WLAN Station
- WLAN Soft AP
BT/BLE Features:
- ESP32 supports BR/EDR and BLE with v4.2
- ESP32-C2/C3/S3 supports BLE v4.2 and v5.0
- ESP32-C6 supports BLE 5.3

1.2 Supported ESP boards

ESP-Hosted-FG solution is supported on following ESP boards:

Supported Targets	ESP32	ESP32-S2	ESP32-S3	ESP32-C2	ESP32-C3	ESP32-C5	ESP32-C6

1.3 Supported Hosts

As mentioned earlier, this version of the solution is primarily targeted to work with MCU based hosts.
Though this solution works with Linux hosts, we recommend other ESP_Hosted-NG flavour for Linux hosts.
ESP-Hosted-FG solution showcase examples for following Linux based and MCU based hosts out of the box.
- MCU Based Hosts
  - STM32 Discovery Board (STM32F469I-DISCO)
  - STM32F412ZGT6-Nucleo 144
- Linux Based Hosts
  - Raspberry-Pi 3 Model B
  - Raspberry-Pi 3 Model B+
  - Raspberry-Pi 4 Model B
You can port this solution to other Linux and MCU platforms using porting guide

1.4 Supported Transports

SDIO Only
- Wi-Fi and Bluetooth, traffic for both runs over SDIO
SDIO+UART
- Wi-Fi runs over SDIO and Bluetooth runs over UART
SPI Only
- Wi-Fi and Bluetooth, traffic for both runs over SPI
SPI+UART
- Wi-Fi runs over SPI and Bluetooth runs over UART

Different ESP chipset support different set of peripherals. Below is features supported matrix for Linux & MCU. In this matrix, Each feature is by default enabled & supported with every trasport in left. Any Unwanted feature can be turned off with config change.

1.5 Feature Matrix

1.5.1 Linux Host

The below table explains which feature is supported on which transport interface for Linux based host.

ESP Chipset	Transport options	Linux Features supported

Note

ESP-Hosted-FG related BR/EDR 4.2 and BLE 4.2 functionalities are tested with bluez 5.43+. Whereas, BLE 5.0 functionalities are tested with bluez 5.45+.
Suggested to use latest stable bluez version.
bluez 5.45 on-wards BLE 5.0 HCI commands are supported.
BLE 5.0 has backward compatibility of BLE 4.2.
ESP32-C5 SDIO and SDIO+UART support is coming soon!

1.5.2 MCU Host

Caution

MCU support in ESP-Hosted-FG is now deprecated. For all MCU-based applications, please use the dedicated ESP-Hosted-MCU repository instead. The information below is kept for backward compatibility only.

The below table explains which feature is supported on which transport interface for MCU based host.

ESP Chipset	Transport options	MCU Features supported

Note:

Bluetooth at MCU
UART is supported from ESP slave side. But not verified from MCU as Host (Works fine with Linux as host)
If you have ported Bluetooth host stack on MCU, you can use ESP32 bluetooth controller in slave mode.
BT/BLE over SPI/SDIO
- BT/BLE support over SPI/SDIO is not readily available. In order to implement it, one needs to:
- Port BT/BLE stack to MCU
- Add a new virtual serial interface using the serial interface API's provided in host driver of ESP-Hosted-FG solution.
- HCI implementation in Linux Driver host/linux/host_driver/esp32 could be used as reference. Search keyword: ESP_HCI_IF
- Register this serial interface with BT/BLE stack as a HCI interface.
BT/BLE over UART
- BT/BLE support over UART is not readily available. In order to implement this, one needs to:
- Port BT/BLE stack to MCU
- Register the UART serial interface as a HCI interface with BT/BLE stack
- With the help of this UART interface, BT/BLE stack can directly interact with BT controller present on ESP bypassing host driver and firmware
- ESP Hosted host driver and a firmware plays no role in this communication
OTA
- Linux hosts support OTA update (Over The Air ESP firmware update) in C and python
- MCU hosts can refer to the same for their development
- For detailed documentation, please read ota_update.md.

2. Hardware and Software setup

This section describes how to set up and use ESP-Hosted-FG solution. Since ESP-Hosted-FG solution supports two distinct platforms, the procedure to use it vastly differs.

2.1 Setup With Linux Host

Please refer to the Setup Guide for Linux host.

2.2 Setup With MCU Host

Caution

MCU support in ESP-Hosted-FG is now deprecated. For all MCU-based applications, please use the dedicated ESP-Hosted-MCU repository instead. The information below is kept for reference purposes only.

Please refer to the Setup Guide for MCU host. In addition to Control path APIs listed below, APIs for MCU specific solution are explained here

3. Control Path

Once ESP-Hosted-FG transport is set up, getting control path working is the first step to verify if the transport is set up correctly
Control path works over ESP-Hosted-FG transport i.e. SPI or SDIO and leverages a way to control and manage ESP from host
The detailed design and procedure to get control path working is explained here
Impatient to evaluate? Please follow our beautiful and intuitive Python based CLI to easily set up the control path

3.1 Control Path APIs

As control path design details, demo application works over control path library using control path APIs.
These APIs are exhaustive list. User can use specific APIs which are of interest.
Each API is explained in a detailed way to kickstart its use.
These Control APIs are common for MPU and MCU based solution.
User can easily integrate ESP-Hosted-FG solution with own project using these APIs and demo application, which implements these APIs.
Control APIs are detailed below.
- Control path APIs

3.2 Demo apps

Demo applications are provided in python and C. Python app makes use of ctypes to implement control APIs.

C demo app
Python demo app

4. Design

This section describes the overall design of ESP-Hosted-FG solution. There are 3 aspects to it:

System Architecture
Transport layer communication protocol
Integration Guide

4.1 System Architecture

This section discusses building blocks of the ESP-Hosted-FG solution for the supported host platforms.

Following are the key building blocks of the system:

ESP-Hosted-FG Driver and Custom Control Path
ESP-Hosted-FG Firmware
Third party components

4.1.1 ESP-Hosted-FG Driver

The components of ESP-Hosted-FG driver are dependent on host platform that is being used. Please refer to the following documents:

System Architecture: Linux based host
System Architecture: MCU based host

4.1.2 ESP-Hosted-FG Firmware

This implements ESP-Hosted-FG solution part that runs on ESP boards. ESP-Hosted-FG firmware is agnostic of the host platform. It consists of the following.

ESP Application
This implements:
- SDIO transport layer
- SPI transport layer
- Virtual serial interface driver
- Control interface command implementation
- Bridges data path between Wi-Fi, HCI controller driver of ESP and Host platform
ESP-IDF Components
ESP firmware mainly uses following components from ESP-IDF. Please check ESP-IDF documentation for more details.
- SDIO Slave driver
- SPI Slave driver
- Wi-Fi driver
- HCI controller driver
- Protocomm Layer

4.1.3 Third Party Components

Third components such as following are essential for end to end working of ESP-Hosted-FG Solution. Implementation or porting of these third party component is not in scope of this project.

TCP/IP and TLS stack
BT/BLE stack
UART driver
Protobuf

4.2 Transport layer communication protocol

This section describes the data communication protocol used at the transport layer. This protocol is agnostic of host platforms that is being used. Please refer to the following links to get more information on communication protocol per transport interface type.

SDIO Communication Protocol
SPI Communication Protocol

4.2.1 Payload Format

This section explains the payload format used for data transfer on SDIO and SPI interfaces.

Host and peripheral makes use of 12 byte payload header which precedes every data packet.
This payload header provides additional information about the data packet. Based on this header, host/peripheral consumes the transmitted data packet.
Payload format is as below

Field	Length	Description
Interface type	4 bits	Possible values: STA(0), SoftAP(1), Serial interface(2), HCI (3), Priv interface(4). Rest all values are reserved
Interface number	4 bits	Unused
Flags	1 byte	Additional flags like `MORE_FRAGMENT` in fragmentation
Packet length	2 bytes	Actual length of data packet
Offset to packet	2 bytes	Offset of actual data packet
Checksum	2 bytes	checksum for complete packet (Includes header and payload)
Reserved2	1 byte	Not in use
seq_num	2 bytes	Sequence number for serial interface
Packet type	1 byte	reserved when interface type is 0, 1 and 2. Applicable only for interface type 3 and 4

4.3 Integration Guide

4.3.1 Porting

Porting for MPU i.e. Linux based hosts is explained here

4.3.3 APIs for MCU Based ESP-Hosted-FG Solution

Below document explains the APIs provided for MCU based ESP-Hosted-FG solution

API's for MCU based host

5. Throughput performance

Station & Soft-AP both the Wi-Fi modes support both, 20 MHz & 40 MHz bandwidth
Throughput performace is measured with iperf inside the RF shielded box
Following are ESP-Hosted-FG iperf throughput numbers for Wi-Fi (station mode - 20MHz), considering common use-case

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