SerialPort BreakState support

[DragonXYZ]

Description

I try to convert a windows SerialPort code to nanoframework,and i noticed nanoframework SerialPort class no not have BreakState,it is old but some protocols are still in use, for example DMX512

How to solve the problem

I searched in google have a solusion https://stackoverflow.com/questions/1279478/rs-232-break-signal
but it is using DllImport

Describe alternatives you've considered

No response

Aditional context

Open source third-party implementation of serial port
https://github.com/jcurl/RJCP.DLL.SerialPortStream/blob/21f60c99621f8d1a6d83a51a9ca2fde6cc22f65e/code/SerialPortStream.cs#L2241
https://github.com/jcurl/RJCP.DLL.SerialPortStream/blob/21f60c99621f8d1a6d83a51a9ca2fde6cc22f65e/dll/serialunix/libnserial/break.c#L27

[josesimoes]

We can't DllImport.
This is the first time I recall seeing this being requested. This is not in our roadmap. Let's keep it open to gather more feedback about the need for such feature.

[DragonXYZ]

I don't mean that DllImport is needed, but the implementation of BreakState has DllImport in it. In the .NET implementation is

Interop.Kernel32.SetCommBreak(this._handle)
[DllImport("kernel32.dll", CharSet=CharSet.Auto, ExactSpelling=false, SetLastError=true)] internal static extern bool SetCommBreak(SafeFileHandle hFile);
So I can't implement this property and method myself.
Is there any way to achieve serialPort->BreakState

We can't DllImport. This is the first time I recall seeing this being requested. This is not in our roadmap. Let's keep it open to gather more feedback about the need for such feature.

[alberk8]

@DragonXYZ ,

This will need changes to the native and managed side of of the SerialPort class. There is need to on the managed side indicate duration of the break and on the native side to calculate the break duration (uart_send_break).

#include "driver/uart.h"
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "esp_log.h"

#define DMX_UART_NUM      UART_NUM_1
#define DMX_TXD_PIN       17
#define DMX_BAUD_RATE     250000
#define DMX_CHANNELS      512

static const char *TAG = "DMX";

void dmx_send_frame(const uint8_t *dmx_data, size_t len) {
    // Send break (logic low) for at least 88 µs
    // At 250,000 baud, 1 bit = 4 µs → 22 bits = 88 µs
    uart_send_break(DMX_UART_NUM, 22);  // 22 bits ~ 88 µs

    // Wait for Mark After Break (MAB), ≥ 8 µs
    ets_delay_us(12);  // Safe MAB value

    // Create full DMX frame: Start Code (0) + channel data
    uint8_t dmx_frame[DMX_CHANNELS + 1];
    dmx_frame[0] = 0;  // Start Code
    memcpy(&dmx_frame[1], dmx_data, len);

    uart_write_bytes(DMX_UART_NUM, (const char *)dmx_frame, len + 1);
    uart_wait_tx_done(DMX_UART_NUM, pdMS_TO_TICKS(20));
}

void app_main(void) {
    // Initialize UART
    uart_config_t uart_config = {
        .baud_rate = DMX_BAUD_RATE,
        .data_bits = UART_DATA_8_BITS,
        .parity    = UART_PARITY_DISABLE,
        .stop_bits = UART_STOP_BITS_2,  // Required by DMX
        .flow_ctrl = UART_HW_FLOWCTRL_DISABLE
    };
    uart_param_config(DMX_UART_NUM, &uart_config);
    uart_set_pin(DMX_UART_NUM, DMX_TXD_PIN, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE);
    uart_driver_install(DMX_UART_NUM, 1024, 0, 0, NULL, 0);

    uint8_t dmx_data[DMX_CHANNELS] = {0};
    dmx_data[0] = 255;   // Example: Channel 1 full on
    dmx_data[1] = 128;   // Example: Channel 2 half on

    while (1) {
        dmx_send_frame(dmx_data, DMX_CHANNELS);
        vTaskDelay(pdMS_TO_TICKS(30));  // DMX refresh rate ~33 FPS
    }
}

[DragonXYZ]

@alberk8 Thanks for your answer, it looks very feasible. But I'm sorry，I am newbie to nanoFramework and cannot compile and test nanoClr and OS by myself. Maybe I need to wait for the nanoFramework team to upgrade @josesimoes