Linux: System.IO.Ports.SerialPort does not open with baudrate 111,865

[DJSures]

area-System.IO

Description

We migrated a working console application from .Net 4.7.2 to .Net 7. The System.IO.Port.SerialPort gives an error with .Net 7 for the baud rate of 111,865. It works on Windows and macOS but does not work on Linux (x64, ARM64, ARM) anymore since the migration from .net 4.7.2 to .net 6. The error "Value does not fall within the expected range" is raised.

       var _sp = new SerialPort(
          "/dev/ttyS0",
          111865,
          0,
          8,
          StopBits.Two,
          Handshake.RequestToSend);
        _sp.Open();

Reproduction Steps

Attempt to open the serial port with the following on Linux

       var _sp = new SerialPort(
          "/dev/ttyS0",
          111865,
          0,
          8,
          StopBits.Two,
          Handshake.RequestToSend);
        _sp.Open();

Expected behavior

No error is thrown, and it works like all .Net Framework did (i.e. 4.7.2)

Actual behavior

An exception is raised for "Value does not fall within the expected range"

Regression?

.Net Framework 4.7.2

Known Workarounds

No response

Configuration

.net 7

Linux (ARM64, ARM, x64)

Other information

No response

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[DJSures]

area-System.IO

Tagging subscribers to this area: @dotnet/area-system-io
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Issue Details

---

area-System.IO

Description

We migrated a working console application from .Net 4.7.2 to .Net 7. The System.IO.Port.SerialPort gives an error with .Net 7 for the baud rate of 111,865. It works on Windows but does not work on Linux (x64, ARM64, ARM) or macOS (ARM, x64) anymore since the migration from .net 4.7.2 to .net 6. The error "Value does not fall within the expected range" is raised.

       var _sp = new SerialDevice(
          "/dev/ttyS0",
          111865,
          0,
          8,
          StopBits.Two,
          Handshake.RequestToSend);
        _sp.Open();

Reproduction Steps

Attempt to open the serial port with the following on Linux or MacOS

       var _sp = new SerialDevice(
          "/dev/ttyS0",
          111865,
          0,
          8,
          StopBits.Two,
          Handshake.RequestToSend);
        _sp.Open();

Expected behavior

No error is thrown, and it works like all .Net Framework did (i.e. 4.7.2)

Actual behavior

An exception is raised for "Value does not fall within the expected range"

Regression?

.Net Framework 4.7.2

Known Workarounds

No response

Configuration

.net 7

Linux (ARM64, ARM, x64)
MacOS (ARM64, x64)

Other information

No response

Author:	DJSures
Assignees:	-
Labels:	area-System.IO, untriaged
Milestone:	-

[janvorli]

@DJSures are you sure the hardware / its driver you are using supports that rate? It looks quite exotic, definitely out of the range of standard baud rates. If that's not the case, .NET cannot do much about it.

[DJSures]

Yes - I have a whole video on it (https://youtu.be/YypZW54wbmU) using a logic analyzer because I was curious at first if that baud would work across macOS, Linux and Windows. But it does because the FTDI hardware supports it. It's a USB to RS422 adapter for the NABU PC. I'm the developer of the Internet Adapter @ https://nabu.ca. The first version of the IA used Mono for a cross-platform GUI and, of course, that baud rate. Due to Mono not working on ARM64 macOS, we needed to compromise and release a CLI using Terminal.GUI. Summary is...

1. it worked with Mono on macOS and Linux
2. it still works with Windows (with .net 7) and also appears to work on macOS x86 (not ARM)
3. the baud is supported because the FTDI driver supports it (any microcontroller would keep it as well because it's just calculating the hardware uart timing based on clock frequency)
4. I copied Mono's SerialPort code from GitHub and added it to my project for fun to see if it would work on Linux. It does, but it won't work on macOS ARM because Mono libraries aren't supported.

I haven't dug into it - but whatever Mono uses for SerialPort works successfully, whereas .Net 7 doesn't.

[danmoseley]

can you share the full stack? that would confirm it is coming from

runtime/src/native/libs/System.IO.Ports.Native/pal_termios.c

Line 350 in ef903fd

int32_t SystemIoPortsNative_TermiosSetSpeed(intptr_t handle, int32_t speed)

[janvorli]

@DJSures thank you for the details. @danmoseley my first guess is that there is some issue in the SystemIoPortsNative_TermiosSetSpeed. It seems that on Linux, we don't attempt to set non-standard rates. Based on what I've find by googling, it seems that cfsetspeed is only capable of setting the standard rates. On macOS, we actually try to use the ioctl(fd, IOSSIOSPEED, ...), but it is possible that the HAVE_IOSS_H is not detected correctly. I have seen subtle problems with the cmake config in the past where things looked correct, but e.g. required adding some compiler option.