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Trying to connect a serial device (3d printer) through the USB port in order to communicate with it (klipper firmware) on an Android device (LOS 18.1/Android 11, 3.18 kernel). But I can't find it in /dev/serial/, it only shows up as /dev/ttyUSB0 and /dev/bus/usb/001/00[^1] and I can't communicate with it through those. I've compiled the kernel with the ch341.c driver. 'lsusb -v' from a chrooted Debian through Linux deploy gives the following output, the device in question is called 'QinHeng Electronics CH340...':

Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 3.00 bDeviceClass 9 Hub bDeviceSubClass 0 bDeviceProtocol 3 bMaxPacketSize0 9 idVendor 0x1d6b Linux Foundation idProduct 0x0003 3.0 root hub bcdDevice 3.18 iManufacturer 3 Linux 3.18.140-Swan-gcb3e40e597b0-dirty xhci-hcd iProduct 2 xHCI Host Controller iSerial 1 xhci-hcd.0.auto bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 wTotalLength 0x001f bNumInterfaces 1 bConfigurationValue 1 iConfiguration 0 bmAttributes 0xe0 Self Powered Remote Wakeup MaxPower 0mA Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 1 bInterfaceClass 9 Hub bInterfaceSubClass 0 bInterfaceProtocol 0 Full speed (or root) hub iInterface 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x81 EP 1 IN bmAttributes 3 Transfer Type Interrupt Synch Type None Usage Type Data wMaxPacketSize 0x0004 1x 4 bytes bInterval 12 bMaxBurst 0 Hub Descriptor: bLength 12 bDescriptorType 42 nNbrPorts 1 wHubCharacteristic 0x000a No power switching (usb 1.0) Per-port overcurrent protection bPwrOn2PwrGood 10 * 2 milli seconds bHubContrCurrent 0 milli Ampere bHubDecLat 0.0 micro seconds wHubDelay 0 nano seconds DeviceRemovable 0x00 Hub Port Status: Port 1: 0000.02a0 5Gbps power Rx.Detect Binary Object Store Descriptor: bLength 5 bDescriptorType 15 wTotalLength 0x000f bNumDeviceCaps 1 SuperSpeed USB Device Capability: bLength 10 bDescriptorType 16 bDevCapabilityType 3 bmAttributes 0x02 Latency Tolerance Messages (LTM) Supported wSpeedsSupported 0x0008 Device can operate at SuperSpeed (5Gbps) bFunctionalitySupport 3 Lowest fully-functional device speed is SuperSpeed (5Gbps) bU1DevExitLat 0 micro seconds bU2DevExitLat 0 micro seconds can't get debug descriptor: Resource temporarily unavailable Device Status: 0x0001 Self Powered Bus 001 Device 003: ID 1a86:7523 QinHeng Electronics CH340 serial converter Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 1.10 bDeviceClass 255 Vendor Specific Class bDeviceSubClass 0 bDeviceProtocol 0 bMaxPacketSize0 8 idVendor 0x1a86 QinHeng Electronics idProduct 0x7523 CH340 serial converter bcdDevice 2.64 iManufacturer 0 iProduct 2 USB Serial iSerial 0 bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 wTotalLength 0x0027 bNumInterfaces 1 bConfigurationValue 1 iConfiguration 0 bmAttributes 0x80 (Bus Powered) MaxPower 98mA Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 3 bInterfaceClass 255 Vendor Specific Class bInterfaceSubClass 1 bInterfaceProtocol 2 iInterface 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x82 EP 2 IN bmAttributes 2 Transfer Type Bulk Synch Type None Usage Type Data wMaxPacketSize 0x0020 1x 32 bytes bInterval 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x02 EP 2 OUT bmAttributes 2 Transfer Type Bulk Synch Type None Usage Type Data wMaxPacketSize 0x0020 1x 32 bytes bInterval 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x81 EP 1 IN bmAttributes 3 Transfer Type Interrupt Synch Type None Usage Type Data wMaxPacketSize 0x0008 1x 8 bytes bInterval 1 can't get debug descriptor: Resource temporarily unavailable Device Status: 0x0000 (Bus Powered) Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 2.00 bDeviceClass 9 Hub bDeviceSubClass 0 bDeviceProtocol 1 Single TT bMaxPacketSize0 64 idVendor 0x1d6b Linux Foundation idProduct 0x0002 2.0 root hub bcdDevice 3.18 iManufacturer 3 Linux 3.18.140-Swan-gcb3e40e597b0-dirty xhci-hcd iProduct 2 xHCI Host Controller iSerial 1 xhci-hcd.0.auto bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 wTotalLength 0x0019 bNumInterfaces 1 bConfigurationValue 1 iConfiguration 0 bmAttributes 0xe0 Self Powered Remote Wakeup MaxPower 0mA Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 1 bInterfaceClass 9 Hub bInterfaceSubClass 0 bInterfaceProtocol 0 Full speed (or root) hub iInterface 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x81 EP 1 IN bmAttributes 3 Transfer Type Interrupt Synch Type None Usage Type Data wMaxPacketSize 0x0004 1x 4 bytes bInterval 12 Hub Descriptor: bLength 9 bDescriptorType 41 nNbrPorts 1 wHubCharacteristic 0x000a No power switching (usb 1.0) Per-port overcurrent protection TT think time 8 FS bits bPwrOn2PwrGood 10 * 2 milli seconds bHubContrCurrent 0 milli Ampere DeviceRemovable 0x00 PortPwrCtrlMask 0xff Hub Port Status: Port 1: 0000.0103 power enable connect can't get device qualifier: Resource temporarily unavailable can't get debug descriptor: Resource temporarily unavailable Device Status: 0x0001 Self Powered

How can I communicate with the serial device? Are there any other kernel modules I should compile? Does newer Android handle serial devices in a different way than Linux does? I've seen other people run this firmware on Android in chrooted Linux like here, here, here. So it is possible, I just must be missing something. I'm happy to post other debugging information/logs.

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/dev/ttyUSB0 would be the Linux kernel default name for most USB-to-serial converters, while /dev/serial/* is probably an alias created by some udev rule. If your Android system has a minimized set of ude rules, it might not include the rule to generate the /dev/serial/* aliases.

The /dev/ttyUSB0 (and any aliases for it, if they exist) is a Unix TTY device interface (basically a serial port + a lot of optional features for dealing with archaic serial terminals) for the USB-to-serial converter. If there is an actual RS-232 serial communication between the converter chip and the actual 3d printer, you might need to set the correct serial port parameters before you can communicate successfully. Even a minimal terminal emulator program such as picocom might help a lot here, although you probably can use stty to make the settings if you have to.

The /dev/bus/usb/*/* devices, on the other hand, expect the program using them to be aware of the functionality of the USB bus. In practice, a program would most likely use the libusb library to deal with those devices.

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