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A very common way to integrate your own I/O drivers is to use an FB interface inside of a library. A much better way, and much more convenient from the usability is the integration in form of a real I/O driver. This approach should always been choosen when you decide to share your driver with others.

To implement an I/O driver in CODESYS you need mainly two things:

  • A device description
  • An FB, implementing the I/O driver interface

In the following you will find some general rules to follow while implementing your driver. Beside this guide, you should check out the different templates for different kinds of drivers to start from. Because in detail the implementation will be diffferent if you implement an SPI driver or you read a value from a sensor using a REST API.

But independent of the kind of driver, which you plan to implement. If you are not routined in writing such software, it is a good idea to prove the access of the hardware directly in an application.

Device Description

Every device, which you can add to your CODESYS project, is described in an XML format inside of a Device Description.

For finetuning and to get a deeper understanding of the format, please check out the schema file. In the following we will just explain the basics to enable you to write your first description.

XML Schema

The XML schema can be downloaded under the URI, which is defined in every XML file:
http://www.3s-software.com/schemas/DeviceDescription-1.0.xsd

Device identification

That the device can be uniquely identified in the device repository on every computer in the world, we need to maintain a few IDs. Please register the ID, which you will be using in the Device Database.

  • Device Type: Either use the matching one from the templates, or use 8000.
  • VendorID: Use 0004, as this is reserved for all public domain drivers
  • DeviceID: Use a unique one, which you added to the Device Database
  • Version: You are free with that, but you should always increase it when you make changes to the device description

Note: The combination of all IDs, described above has to be globally unique. Official versions of a driver with the same IDs, but different content shall never exist.

Connector

A device or module, which you can add to the device tree in CODESYS contains at least one connector. This connector is used to attach the module to a parent device.

    <Connector moduleType="8023" interface="Common.PCI" role="child" explicit="false" connectorId="1" hostpath="-1">
      <InterfaceName name="local:PCI">PCI-Bus</InterfaceName>
      <Slot count="1" allowEmpty="false"></Slot>
    </Connector>
  • moduletype: use 8000 + the DeviceID. This way you make sure, that you have no conflicts with other public domain drivers.
  • interface: For submodules, like SPI, I2C, or similar, use the interface from the template. For all others, you can use Common.PCI. This interface can be easily attached to most PLCs.
  • ConnectorID: simply enumerate the connectors within your modules. This ID is only used to specify the so called "host path"

Interfaces

Interfaces are symbolic names to match compatible connectors, so to find compatible devices or modules. We have some different concepts to configure our device tree in CODESYS.

  • Variable Connectors
    You don't see anything in the device tree. But when you click on "Add Device" you get a list of all devices, which are providing an interface, that is compatible to the interfaces of the parent. The number of allowed devices which can be added to a variable connector can be varied.
    <Connector moduleType="8023" interface="OpenSource:Internal" role="parent" explicit="false" connectorId="2" hostpath="1">
      <InterfaceName name="local:internal">Internal</InterfaceName>
      <Var max="4"></Var>
  • Fix connectors
    Fix connectors are very similar to Variable connectors, but the devices are added implicitely and can't be changed.
    <Connector moduleType="8023" interface="OpenSource:FixConnectorInterface" role="parent" explicit="false" connectorId="2" hostpath="1">
      <InterfaceName name="local:internal">Internal</InterfaceName>
      <Fixed>
        <!-- This is an example of a fixed module specified in the same file -->
        <Module>
          <LocalModuleId>8023</LocalModuleId>
        </Module>
        <!-- This is an example of a fixed module specified by DeviceIdentification. The defininition of this module is in another *.devdesc.xml -->
        <Module>
          <DeviceIdentification deviceType="40107" deviceId="0001 bcde" version="3.5.9.0"/>
        </Module>
      </Fixed>
  • Slots
    Slots are again similar to variable slots. But the user can see the slot in the device tree. Because every slot has a fix place in the tree, and because the user can plug and remove the devices, the specialty for the driver is, that there can be empty slots.

This was a huge preamble for an easy topic. But it was important that you get an idea of how the result will look like.

Interfaces are easy. You define one interface per child connector and one for every parent connector. There are no fix restrictions for the interface names. But it is an unofficial rule, that they should be prefixed with a short or full name of the vendor.

      <Connector ConnectorId="2" HostPath="-1" interface="MyCompany.A" moduleType="40101"
                 role="parent">
         <Slot allowEmpty="false" count="16"/>
      </Connector>
      <Connector ConnectorId="3" HostPath="-1" interface="MyCompany.B" moduleType="40102"
                 role="parent">
         <Slot allowEmpty="false" count="16"/>
      </Connector>
...
   <Modules>
      <Module>
         <ModuleId>1701</ModuleId>
         <DeviceInfo>
            <Name name="localStrings:Name1704">Digital Input</Name>
            <Description name="localStrings:Desc1704"/>
            <Vendor name="localStrings:3S">3S-Smart Software Solutions</Vendor>
            <OrderNumber/>
         </DeviceInfo>
         <Connector ConnectorId="2" HostPath="-1" interface="MyCompany.A" moduleType="41101"
                    role="child">
            <Slot allowEmpty="false" count="1"/>
            <HostParameterSet>
               <Parameter ParameterId="1000" type="std:BIT">
                  <Attributes channel="input" download="true" functional="false" offlineaccess="readwrite"
                              onlineaccess="readwrite"/>
                  <Default>0</Default>
                  <Name name="local:in1">in1</Name>
               </Parameter>
            </HostParameterSet>
         </Connector>
      </Module>
      <Module>
         <ModuleId>1702</ModuleId>
         <DeviceInfo>
            <Name name="localStrings:Name1705">Digital Output</Name>
            <Description name="localStrings:Desc1705"/>
            <Vendor name="localStrings:3S">3S-Smart Software Solutions</Vendor>
            <OrderNumber/>
         </DeviceInfo>
         <Connector ConnectorId="3" HostPath="-1" interface="MyCompany.A" moduleType="41102"
                    role="child">
            <Slot allowEmpty="false" count="1"/>
            <HostParameterSet>
               <Parameter ParameterId="1000" type="std:BIT">
                  <Attributes channel="output" download="true" functional="false" offlineaccess="readwrite"
                              onlineaccess="readwrite"/>
                  <Default>0</Default>
                  <Name name="local:in1">in1</Name>
               </Parameter>
            </HostParameterSet>
         </Connector>
      </Module>
      <Module>
         <ModuleId>1703</ModuleId>
         <DeviceInfo>
            <Name name="localStrings:Name1705">Digital Output</Name>
            <Description name="localStrings:Desc1705"/>
            <Vendor name="localStrings:3S">3S-Smart Software Solutions</Vendor>
            <OrderNumber/>
         </DeviceInfo>
         <Connector ConnectorId="4" HostPath="-1" interface="MyCompany.B" moduleType="41103"
                    role="child">
            <Slot allowEmpty="false" count="1"/>
            <HostParameterSet>
               <Parameter ParameterId="1000" type="std:BIT">
                  <Attributes channel="output" download="true" functional="false" offlineaccess="readwrite"
                              onlineaccess="readwrite"/>
                  <Default>0</Default>
                  <Name name="local:in1">in1</Name>
               </Parameter>
            </HostParameterSet>
         </Connector>
      </Module>
      <Module>
         <ModuleId>1704</ModuleId>
         <DeviceInfo>
            <Name name="localStrings:Name1706">PWM Output</Name>
            <Description name="localStrings:Desc1706"/>
            <Vendor name="localStrings:3S">3S-Smart Software Solutions</Vendor>
            <OrderNumber/>
         </DeviceInfo>
         <Connector ConnectorId="5" HostPath="-1" interface="MyCompany.B" moduleType="41104"
                    role="child">
            <Slot allowEmpty="false" count="1"/>
         </Connector>
      </Module>
   </Modules>

Parameter Set

A device can roughly hold two kinds of parameters:

  • configuration parameters, which are important to initialize the I/O system
  • I/O channels, which can be mapped to variables

I/O Channels

Data types, default values, etc. are defined equally for all kinds of parameters. But there is a significant difference in how the different kinds of parameters are processed.

I/O channels are processed in the same way as configuration parameters, thus they have additional mapping information assigned to it, so that they are also passed on to IoDrvReadInputs/-WriteOutputs.

I/O channels are marked with the "channel" attribute.

<Attributes channel="input" download="true" functional="false" offlineaccess="write" onlineaccess="readwrite" />

Other parameter attributes

  • Download specifies if the parameter is downloaded as part of the connectorlist, that is passed to IoDrvUpdateConfiguration
  • Functional specifies if reading or writing the parameter results in a function call to IoDrvReadParamet/-WriteParameter
  • Online-/OfflineAccess defines the allowed permissions in online or offline mode.

Datatypes

Both can be configured with the same structured datatypes.

They can be located globally on device level, then they are called DeviceParameters. If they are part of the device that the user adds to the tree, then, they are called HostParameters and attached to one of its connectors.

You can use virtually every datatype for a parameter, which can be used in IEC61131. This includes especially arrays and structures.
But you have to be aware that you need to define those datatypes consistently twice (in your driver library and your device description). There is no extra check. If they don't match between your device description and your code, it will just not work, crash, or whatever...

Some examples...

Basic datatypes

Basic datatypes don't need a declaration. They can be used with the namespace prefix "std". So "std:BOOL" is the equivalent of a BOOL datatype in IEC.

DevDesc:

        <Parameter ParameterId="1000" type="std:DWORD">
          <Attributes channel="input" download="true" functional="false" offlineaccess="write" onlineaccess="readwrite" />
          <Default>0</Default>
          <Name name="local:DWIN">DWORD Input</Name>
          <Description name="local:DWIN.Desc">DWORD Input</Description>
        </Parameter>

Structures

IEC:

TYPE DUT :
STRUCT
    BYTE1 : BYTE;
    BYTE2 : BYTE;
    BYTE3 : BYTE;
    BYTE4 : BYTE;
END_STRUCT
END_TYPE

DevDesc:

   <StructType name="local:Channel4Byte">
      <Component identifier="Byte0" type="std:BYTE">
        <Default />
        <VisibleName name="local:Byte0">Byte0</VisibleName>
      </Component>
      <Component identifier="Byte1" type="std:BYTE">
        <Default />
        <VisibleName name="local:Byte1">Byte1</VisibleName>
      </Component>
      <Component identifier="Byte2" type="std:BYTE">
        <Default />
        <VisibleName name="local:Byte2">Byte2</VisibleName>
      </Component>
      <Component identifier="Byte3" type="std:BYTE">
        <Default />
        <VisibleName name="local:Byte3">Byte3</VisibleName>
      </Component>
    </StructType>
    ...
        <Parameter ParameterId="1000" type="local:Channel4Byte">
          <Attributes channel="input" download="true" functional="false" offlineaccess="write" onlineaccess="readwrite" />
          <Default>0</Default>
          <Name name="local:DWIN">DWORD Input</Name>
          <Description name="local:DWIN.Desc">DWORD Input</Description>
        </Parameter>

Bit Channels

IEC:

TYPE DUT :
STRUCT
    BYTE1 : BYTE;
    BYTE2 : BYTE;
    BYTE3 : BYTE;
    BYTE4 : BYTE;
END_STRUCT
END_TYPE

DevDesc:

    <BitfieldType basetype="std:BYTE" name="Bitfield">
      <Component identifier="Bit0" type="std:BOOL">
        <Default />
        <VisibleName name="local:Bitfield.Bit0">Bit0</VisibleName>
      </Component>
      <Component identifier="Bit1" type="std:BOOL">
        <Default />
        <VisibleName name="local:Bitfield.Bit1">Bit1</VisibleName>
      </Component>
      <Component identifier="Bit2" type="std:BOOL">
        <Default />
        <VisibleName name="local:Bitfield.Bit2">Bit2</VisibleName>
      </Component>
      <Component identifier="Bit3" type="std:BOOL">
        <Default />
        <VisibleName name="local:Bitfield.Bit3">Bit3</VisibleName>
      </Component>
      <Component identifier="Bit4" type="std:BOOL">
        <Default />
        <VisibleName name="local:Bitfield.Bit4">Bit4</VisibleName>
      </Component>
      <Component identifier="Bit5" type="std:BOOL">
        <Default />
        <VisibleName name="local:Bitfield.Bit5">Bit5</VisibleName>
      </Component>
      <Component identifier="Bit6" type="std:BOOL">
        <Default />
        <VisibleName name="local:Bitfield.Bit6">Bit6</VisibleName>
      </Component>
      <Component identifier="Bit7" type="std:BOOL">
        <Default />
        <VisibleName name="local:Bitfield.Bit7">Bit7</VisibleName>
      </Component>
    </BitfieldType>
   <StructType name="local:Channel4Byte">
      <Component identifier="Byte0" type="local:Bitfield">
        <Default />
        <VisibleName name="local:Byte0">Byte0</VisibleName>
      </Component>
      <Component identifier="Byte1" type="local:Bitfield">
        <Default />
        <VisibleName name="local:Byte1">Byte1</VisibleName>
      </Component>
      <Component identifier="Byte2" type="local:Bitfield">
        <Default />
        <VisibleName name="local:Byte2">Byte2</VisibleName>
      </Component>
      <Component identifier="Byte3" type="local:Bitfield">
        <Default />
        <VisibleName name="local:Byte3">Byte3</VisibleName>
      </Component>
    </StructType>
    ...
        <Parameter ParameterId="1000" type="local:Channel4Byte">
          <Attributes channel="input" download="true" functional="false" offlineaccess="write" onlineaccess="readwrite" />
          <Default>0</Default>
          <Name name="local:DWIN">DWORD Input</Name>
          <Description name="local:DWIN.Desc">DWORD Input</Description>
        </Parameter>

Driver Interface

Please always start with a template, when you start writing a driver. This will give you a good skeleton of your driver. Anyway, this chapter contains a few basic informations about specific interface functions.

IoDrvUpdateConfiguration

This is always the first entry point when you start writing a driver. It is called when a program is loaded, and gives all drivers the chance to register itself for specific connectors of the device tree.

Additionally it gives the driver the chance to prepare itself and to configure the I/O system.

This function is called with pConnectorList set to 0, when the application is deleted or reseted. So all drivers need to handle that.

IF (pConnectorList = 0) THEN
    RETURN;
END_IF

Registering for a connector

Check the template for details. In general you search for a connector by its "Module ID" . Then you register your base interface pointer at this connector.

This is enough, that you are called by the I/O manager for every I/O update.

IF m_pConnector^.hIoDrv = 0 THEN
    m_pConnector^.hIoDrv := m_hInterface;

Reading Configuration

You get the whole built time configuration of the application passed to this function. Read those values with IoMgrConfigReadParameter to configure your subsystem.

Preparing I/O channels

The I/O channels are also just a special type of parameter, and can be read in this early stage. You can use the value "dwDriverSpecific" to prepare your I/Os in a way that you can quickly access them later on.

The best way is to store a pointer to the I/O data there. Those can be perfectly used with IoMgrCopy... in IoDrvReadInputs/-WriteOutputs.

    FOR i:=0 TO 7 DO
        pParameter := IoMgrConfigGetParameter(m_pConnector, 1000 + i);
        IF (pParameter <> 0) THEN
            pParameter^.dwDriverSpecific := ADR(_MCP3008.auiValue[i]);
        END_IF
    END_FOR

IoDrvReadInputs / Iodrvwriteoutputs

CODESYS reduces the updates of the I/O to the bare minimum. The compiler detects already which I/O is used in which task, and calls the drivers from those task contexts in which they are used.

To allow the driver to update only the necessary I/O variables, you get a list of mappings passes to those functions.

FOR i:=0 TO nCount - 1 DO
    IF (pConnectorMapList[i].dwNumOfChannels = 0) THEN
        CONTINUE;
    END_IF
    FOR j:= 0 TO UDINT_TO_UINT(pConnectorMapList[i].dwNumOfChannels) - 1 DO 
        IoMgrCopyInputLE(ADR(pConnectorMapList[i].pChannelMapList[j]), pConnectorMapList[i].pChannelMapList[j].pParameter^.dwDriverSpecific);
    END_FOR
END_FOR

Related

Documentation: IndexMain

Discussion

  • aliazzz

    aliazzz - 2018-09-30

    <attributes download="true" offlineaccess="write" functional="false" channel="input" onlineaccess="readwrite"></attributes>

    => Please explain these meta tags, as they are important ;-)

     
    • Ingo

      Ingo - 2018-10-06

      I tried to explain that by reworking parts of this chapter. Hope it helps...

       
      • aliazzz

        aliazzz - 2018-10-20
         

        Last edit: aliazzz 2019-01-18
  • aliazzz

    aliazzz - 2018-10-20

    ...

     

    Last edit: aliazzz 2018-10-20

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