FT232H I2C Multi byte reads does not work

[gabbla]

TL;DR Reading more than 1 byte using the FT232H I2C bus result in a bus lock. The single byte reads work as expected.

I am writing a program to control a test bench which is equipped with several IO expanders (PCA9554), a temperature sensor SHT31 and and ADC (ADS7828). The bench is connected to the PC via a FT232H based cable. I am able to interact with the IOEXPs just fine, but when I need to read a temperature or an ADC channel the bus stalls. I investigated further on the ADC side and found that reading more than 1 byte results in a unusable bus.

The reading process is simple: write the channel you want to read, then read 2 bytes.

The hardware has been validated with a nucleo, which works as expected:

The above Logic2 captures are available: ft232h_dotnet.zip.

Steps to reproduce

Since the ADS7828 is not available in the library, I wrote my driver. I guess you can try to read more than 1 byte from any device and get the same issue.

        public short Read(InputMultiplexer ch)
        {
            Span<byte> writeBuff = stackalloc byte[1]
            {
                ChannelToByte(ch)
            };
            Span<byte> readBuff = stackalloc byte[2];

            i2cDevice.WriteRead(writeBuff, readBuff);
            return BinaryPrimitives.ReadInt16BigEndian(readBuff);
        }

Expected behavior

It should be possible to read more than 1 byte while using the FT232H binding.

Versions used

dotnet --info
.NET SDK:
 Version:   7.0.101
 Commit:    bb24aafa11

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.19045
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\7.0.101\

Host:
  Version:      7.0.1
  Architecture: x64
  Commit:       97203d38ba

.NET SDKs installed:
  7.0.101 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 3.1.32 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 6.0.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 7.0.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 3.1.32 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 7.0.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.1.32 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 6.0.12 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 7.0.1 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
  x86   [C:\Program Files (x86)\dotnet]
    registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\x86\InstallLocation]

Environment variables:
  Not set

global.json file:
  Not found

Learn more:
  https://aka.ms/dotnet/info

Download .NET:
  https://aka.ms/dotnet/download

• System.Device.Gpio 2.3.0-prerelease.22520.10
• Iot.Device.Bindings 2.3.0-prerelease.22520.10

[Ellerbach]

Yes, you are write. This is a limitation and should be addressed. It seems there are few more issues with the FT232H. This should require investigations.

[Ellerbach]

Note FT4222 has been proved to work nicely: https://github.com/dotnet/iot/tree/main/src/devices/Ft4222

So that can be a good solution for you as well.

[gabbla]

Thank you for the confirmation. I'll take a look during the holidays to see if I can spot anything strange. Unfortunately I need to stick to the FT232 since my company has stocked several units. Thanks for the suggestion tho!

Gab

[Ellerbach]

Closing this one as seems to be fixed by the last PR!