cs-pcan-usb

NodeJS PCAN-USB Module

This module provides a NodeJS interface to the PEAK-System PCAN-USB adapter, and possibly others that are supported by the PCAN-Basic library.

This module is meant to serve as a drop-in replacement for can-usb-com, allowing the PCAN-USB adapter to be used in place of GridConnect CAN-USB-COM.

This module uses native code through N-API and currently supports Windows and macOS.

Getting Started

The following assumes that NodeJS is already installed. This module was developed using Node v12.18.4 for Windows 10 x86_64 and macOS 10.15.6.

To install this module, run:

npm install cs-pcan-usb

The following is a sample script that opens the CAN port, writes a single message to the bus, and listens for and prints received messages from the bus.

const Can = require('cs-pcan-usb');

let can = new Can({
  canRate: 250000,
});

can.list()
  .then((ports) => {
    console.log(ports);
    return can.open(ports[0].path)
      .catch((err) => {
	console.error(err);
	process.exit(1);
      });
  })
  .then(() => {
    can.write({ id: 0x10EF8001,
                ext: true,
                buf: Buffer.from([0x45, 0x00, 0x00, 0x04, 0x00, 0x00]) });
  })
  .catch((err) => {
    console.error(err);
    can.close();
    process.exit(1);
  });


can.on('data', function(msg) {
  console.log(JSON.stringify(msg, (key, value) => {
    if ((typeof value === 'number') && (key == "id")) {
      return value.toString(16).toUpperCase().padStart(8, '0');
    } else if (typeof value === 'number') {
      return value.toString(16).toUpperCase().padStart(2, '0');
    } else {
      return value;
    }
  }));
});

Examples

Both JavaScript and Win32 examples are available in the example folder.

Configuration

The constructor accepts an object that specifies the desired configuration. The CAN adapter is set up before the open method resolves, so once it is complete, the CAN interface is ready for use.

The default options are shown in the following example. Any of them may be omitted from the constructor's option object to use their default value.

let can = new Can({

  // bit rate on the CAN bus
  canRate: 250000,

  // filters for incoming packets
  filters: [
  ],

  // useful for testing, each sent packet is also received
  loopback: false,
  });

Streaming

cs-pcan-usb extends the NodeJS stream interface, so it can be piped into other stream instances.

Filtering

⚠️ Due to limitations of MacCAN and PCBUSB, CAN message filtering is not supported on macOS.

By default, all CAN message are captured, but this can be limited by applying a message filter. The following are examples of filter definitions that are passed to the open method.

{
  ext: true, // Applies to extended (29-bit IDs)
  id: '10EF0000 10EFFFFF', // Allow IDs 0x10EF0000 through 0x10EFFFFF
}

{
  ext: true, // Applies to extended (29-bit IDs)
  fromID: 0x10EF0000, // Allow IDs 0x10EF0000 through 0x10EF7777
  toID: 0x10EF7777,
}

{
  ext: false, // Applies to standard (11-bit IDs)
  code: 0x081, // Acceptance code
  mask: 0x0F8, // Acceptance mask
}

The PCAN-USB adapter supports one message filter at a time. If multiple filters are applied, the resulting filter spans the range of the highest to lowest IDs of all filters.

Three filter formats are supported by the package:

• code and mask format, directly specifying the acceptance filter with a code and mask

   `code: 0x10EF0000, mask: 0xFFFF0000`
  

• fromID and toID format, specifying a range of IDs to be accepted by the filter:

   `fromID: 0x10EF0000, toID: 0x10EFFFFF`
  

• id format, specifying a string with a range of IDs to be accepted by the filter:

   `id: '10EF0000 10EFFFFF'`
  

When using the start/stop or id formats, it is not guaranteed that all messages outside of the specified range will be filtered out. This is due to a hardware limitation reported in the PCAN-Basic documentation.

Given a range of IDs to allow, it is possible to convert to an acceptance code and mask pair:

acceptance_code = fromID & toID
acceptance_mask = ~(fromID ^ toID)

Mixing Filter Types

Internally, the PCAN-USB adapter does not differentiate between standard and extended ID filtering. The ext property is only made available for compatibility with can-usb-com and cs-canlib.

As such, a filer specification like

{ ext: true, id: '00000000 FFFFFFFFF' }

will allow all messages with standard IDs (000 through 7FF) through to the receive buffer. This is not consistent with can-usb-com or cs-canlib, which follow CAN-USB-COM's specification:

• When [filtering is] disabled, all CAN messages are received regardless of the definitions in the list
• When [filtering is] enabled, only messages which match filter definitions in the list will be passed through.

JavaScript Events

The module emits the following events:

• open when the serial port is successfully opened
• error if an error occurs
• data when an incoming CAN bus frame is received
• write when an outgoing CAN bus frame is sent to the device (the event is emitted before the frame is actually sent on the bus)
• close when the port is closed

To listen for the events, use the typical NodeJS EventEmitter pattern:

  can.on('open', function(){
    console.log( 'CAN bus opened');
  })

  can.on('data', function(msg){
    console.log( msg );
  })

  can.on('close', function(err){
    if( err && err.disconnected ) {
      console.log( 'CAN bus disconnected' );
    }
    else {
      console.log( 'CAN bus closed by application' );
    }
  })

  can.on('error', function(err){
    console.log( 'CAN bus error: ', err );
  })

Asynchronous Message Reception and Callbacks

This module takes advantage of the asynchronous message receive notification offered by the PCAN-Basic API. It implements a 'light' callback function in the native code, which simply calls the JavaScript function provided when the event is enabled using pcan.EventEnable(). The JavaScript function is then expected to call pcan.Read() to retrieve the newly received message, which uses the API's CAN_Read() function behind-the-scenes.

In the future, it may make sense to move the call to CAN_Read() directly into the native code to improve performance.

Win32 Events

The Windows version of this module provides a Win32 event to the PCAN-Basic API through the CAN_SetValue(PCAN_RECEIVE_EVENT) API call, which gets signaled upon receipt of a CAN message that is accepted by the message filter. A Win32 thread waits on the event using WaitForMultipleObjects, invokes a callback function when signaled, and resets itself for the next message.

Unix Pipes

Under the MacCAN PCBUSB library, this module uses the read-end of a POSIX pipe, received through the CAN_GetValue(PCAN_RECEIVE_EVENT) API call. A POSIX thread waits for data to be written to the pipe using select(2), invokes a callback function when signaled, and resets itself for the next message.

API

This module's API functions generally return Promises, which are resolved or rejected when a request is complete.

Refer to the documentation on Promises for details on how to chain requests together, detect errors, etc.

Refer to the PCAN-Basic documentation for details on the full API that this module implements.

Development

Before updating or modifying this package, please

• Lint any changes using eslint.
• Confirm that unit tests pass, noting the exceptions described in the next section.

In order to run unit tests (npm test), at least one PCAN-USB device must be connected to the computer.

The pingpong test is currently configured to use cs-pcan-usb for one adapter, and can-usb-com for the other. These must be connected via a properly terminated bus.

Do not run any tests on a bus with active traffic, since receiving unexpected CAN packets may confuse the tests.

Build Environment Setup

Windows 10 x86 64-bit

1. Install NodeJS. Version 12.18.4 is known to work as of the time of writing. Ensure that node and npm are found when invoked through the Command Prompt. If not, add the appropriate paths to the user's PATH environment variable.
2. Install the windows-build-tools Node package by running the following in an administrative Command Prompt or PowerShell window:
   • npm install -g windows-build-tools
3. Exit the administrative console after this completes and use a console with normal privileges for the rest of the setup
4. Clone the cs-pcan-usb repository: git clone https://github.com/rapomon/cs-pcan-usb
5. Install dependencies:
   • cd cs-pcan-usb\
   • npm install
6. Build:
   • node-gyp clean
   • node-pre-gyp configure
   • node-pre-gyp build
7. Test:
   • npm test
8. Clean build directory: (optional; perform as necessary)
   • node-gyp clean

macOS x86 64-bit

1. Install NodeJS. Version 12.18.4 is known to work as of the time of writing. Ensure that node and npm are found when invoked through a Terminal session. If not, add the appropriate paths to the user's PATH environment variable.
2. Install Xcode and the Command Line Tools using the App Store. Version 12.0.1 is known to work as of the time of writing.
3. Clone the cs-pcan-usb repository: git clone https://github.com/rapomon/cs-pcan-usb
4. Install dependencies:
   • cd cs-pcan-usb\
   • npm install
5. Build:
   • node-gyp clean
   • node-pre-gyp configure
   • node-pre-gyp build
6. Test:
   • npm test
7. Clean build directory: (optional; perform as necessary)
   • node-gyp clean

Build Notes

Depending on shell or executable path configuration, it may be necessary to use npx to execute node-pre-gyp.

If the test stage fails, useful error messages may be hidden by mocha. When tracking down a the cause of an error, running the example code directly, for example node example/js/test.js, may be helpful.

It may also be helpful to recompile the module with CANLIB_DEBUG and CANLIB_EVENT_DEBUG defined to enable debugging messages.

Distribution

As part of the installation process, the platform-specific binary portion of the native addon is retrieved from a separate GitHub repository at @csllc/cs-pcan-usb-binding. This allows the cs-pcan-usb module to be installed on machines that do not have a full development environment set up to build it from source.

This package is configured such that npm install will attempt to download the pre-built binary first, and fall back onto building from source if that fails.

Building and Packaging for Distribution

After incrementing the package version number in this repository, the following commands can be used to generate a corresponding binary package for release.

• node-pre-gyp configure
• node-pre-gyp build
• node-pre-gyp package

Depending on shell or executable path configuration, it may be necessary to use npx to execute the above commands.

Afterwards, create a new release in @csllc/cs-pcan-usb-binding using the same new version number and attach the .tar.gz file found in build/stage/{version}/.

Functionality Limitations

Questionable Functionality

The following have been observed as potential sources of unexpected behavior in the future.

• No error is thrown when the PCAN-USB dongle is unplugged while the module is running.
• The PCAN-Basic API does not provide the means to enable a CAN adapter's loopback ("self-receive" or "echo") feature. This is instead simulated in cs-pcan-usb by pushing data passed to the write method back into the receive data stream.
• As a result of the above, the expected outcome of the test units (npm test) is that all pass except those in filter.test.js that test should.not.emit('data'). This does not indicate that the filter functionality does not work.
• The macOS build of this addon does not support filtering at all, and any attempts to use pcan.FilterMessages, pcan.AcceptanceFilter11Bit, and pcan.AcceptanceFilter29Bit will fail silently.
• The PCAN-USB adapter does not differentiate between extended and standard filters; see the notes under Filtering, above.

Untested Functionality

The following have not been tested due to hardware availability.

• All FD functions (CAN_InitializeFD, CAN_ReadFD, CAN_WriteFD)
• Enumerating more than one PCAN device connected to a computer