Library asynchronous mode for Web port. (ESF-223)

[Maksons]

Is your feature request related to a problem?

Hello,

Most (or all) function in library are synchronous, Serial Receive/Transmit wait until it's finished.
I would like to use this library in Web/JavaScript with help of Emscripten, but it prefer asynchronous operations ( Serial/UART receive happen when not busy checking it ).
So question is how hard it would be to convert this library to asynchronous ?

Describe the solution you'd like

I see it as some type of state machine, with states / substates :

• Idle state
• Connecting
• Reading
• Flashing
• etc

Sub-states like:

• Idle
• Processing data
• Waiting for data receive (from Serial/UART )
• Waiting for data sent out (over Serial/UART )

Describe alternatives you've considered

Would be happy to hear possible alternatives...

Additional context

No response

[github-actions]

Hi @Maksons! Please be aware that (1) the following suggestions are generated by a bot and haven't been fact-checked by Espressif Systems, (2) burning eFuses and enabling security features are irreversible operations and can damage your ESP32 device. We hope that this message will help you until an Espressif Engineer looks at your issue.

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Based on the GitHub issue, it appears the user is looking to implement asynchronous UART operations for use with Emscripten in a web/JavaScript environment. The Espressif documentation provides several relevant examples and approaches for handling asynchronous UART operations.

Asynchronous UART Options in ESP-IDF

ESP-IDF provides multiple approaches for handling UART operations in both blocking and non-blocking ways:

1. Default UART VFS Behavior: By default, UART writes are blocking (busy-wait until data is in FIFO) while reads are non-blocking (only returning data present in FIFO). This default behavior might not be ideal for your web application needs with Emscripten.
   ESP32 Standard I/O Guide

2. Interrupt-Driven Approach: You can switch to the driver's interrupt-driven functions using uart_vfs_dev_use_driver() or revert to non-blocking with uart_vfs_dev_use_nonblocking().
   ESP32 Standard I/O Guide

3. Asynchronous Tasks Example: There's an example specifically demonstrating asynchronous UART communication using separate tasks:

   • uart_async_rxtxtasks - Shows how to use two asynchronous tasks for UART communication, with one task transmitting and another receiving
     ESP32 UART Reference

4. Event-Driven Approach: The uart_events example demonstrates how to handle UART events asynchronously:

   • This could align well with your state machine concept
     ESP32 UART Reference

5. Non-blocking I/O Multiplexing: The uart_select example shows how to use select() for non-blocking I/O multiplexing:

   • This allows for handling multiple I/O sources without blocking
     ESP32 UART Reference

Recommendations for Your Web/JavaScript Implementation

For your Emscripten-based web application, I would recommend:

1. Examine the uart_async_rxtxtasks and uart_events examples as starting points
2. Consider implementing your state machine based on the event-driven model
3. Use the fcntl function with O_NONBLOCK flag when working with the interrupt-driven driver to ensure non-blocking behavior

The state machine approach you outlined (Idle, Connecting, Reading, Flashing, etc.) aligns well with how ESP-IDF's event-driven UART examples are structured, making it a feasible path forward.

[Dzarda7]

Hi @Maksons, it sounds like a nice usecase! Sorry, I am not that familiar with web development. But I believe that if this library is synchronous or asynchronous is the matter of port implementation. For example esp32_port might look synchronous, but in reality the library runs in a task and many functions used from ESP-IDF and every delay let the scheduler switch to another task, so it can be used asynchronously. I believe that the same thing can be done in your case, it is just the question of implementation of the port. I do not know if it is something you are looking for, but this can be helpful. There in the README is described what you need to do in order to implement custom port, but you can have more helper functions there.

Also, not sure if you are familiar with that, but there is also esptool-js. But I will be happy if you decide for this library 😄 just it might be harder for you to implement.

[Dzarda7]

Hello @Maksons, there might be push to try intergrate esp-serial-flasher into some javascript. Can you elaborate a bit on what you think needs to be done?

[Maksons]

Sorry,
It looks like nothing simple could be done to get it work asynchronous.
There are ways to get synchronous code to work in Web.
And WebSerial / WebUSB functions need be implemented and with extra workarounds for synchronous code.
So, this question could be closed.
Should I close it or there are something to discuss more ?

[Dzarda7]

No, keep this open. I will try to look into it. Thanks for the idea.

[Dzarda7]

@Maksons just out of curiosity, did you implement this or ended up using different solution? Thanks.