TMDS64GPEVM: EtherCAT communication

I had few more questions to add to the above one.

• I noticed that main is declared as int main(int argc, char *argv[]) in the simple etherCAT slave example. Why is it done in this way?
• Does the Simple EtherCAT slave example send any packets to the master upon initialisation of the etherCAT stack? This question is the based on the understanding that the example initialises the etherCAT stack. Please correct me if I am wrong.
• Is there any documentation for the etherCAT examples (at least for the simple EtherCAT slave example) provided, apart from the one provided by the sdk? 

Hi

Aaron Renny said:

is it possible to configure the board to act as a master ?

No. SDK provides examples for EtherCAT Slave only.

Aaron Renny said:

I noticed that main is declared as int main(int argc, char *argv[]) in the simple etherCAT slave example. Why is it done in this way?

These arguments are not used. You can ignore them.

Aaron Renny said:

Does the Simple EtherCAT slave example send any packets to the master upon initialisation of the etherCAT stack? This question is the based on the understanding that the example initialises the etherCAT stack. Please correct me if I am wrong.

No, slave does not send packets. In EtherCAT, typically master sends packets and slaves process it "on-the-fly" and update it.

Aaron Renny said:

Is there any documentation for the etherCAT examples (at least for the simple EtherCAT slave example) provided, apart from the one provided by the sdk? 

No. I assume that you have already checked the links from this page.

Regards
Dhaval Khandla

Hi

Aaron Renny said:

is it possible to configure the board to act as a master ?

You can implement this using ICSSG EMAC. You can either use open source masters or talk to some one like Acontis. No direct support is available from TI as of now.

Please check this thread for more details : https://e2e.ti.com/support/processors-group/processors/f/processors-forum/159104/ethercat-master-in-am335x

Regards
Dhaval Khandla

Hi Dhaval

Thanks for the reply. I was going through the Simple EtherCAT example and i came across some functions to which i could not find any function definitions. They are listed below.

OSAL_init()

OSAL_startOs()

EC_API_SLV_load

EC_API_SLV_prepareTasks

EC_API_SLV_run

Can you tell me where the body of these functions are written? 

We would like to setup a system in which a master and slave communicates through etherCAT. Can such a system be setup with PC as master and am64xEVM board as slave? Please do give the steps to set up if it is possible.

Thank you.

Hi

Aaron Renny said:

OSAL_init()

OSAL_startOs()

EC_API_SLV_load

EC_API_SLV_prepareTasks

EC_API_SLV_run

These functions are a part of stack library and not required for customizing slave product. Stack APIs are documented in this page.

Aaron Renny said:

Can such a system be setup with PC as master and am64xEVM board as slave? Please do give the steps to set up if it is possible.

Yes, this is possible. You can build the example first as described here , and then follow steps from this page to setup communication between TwinCAT on PC and slave running on AM64x.

Regards
Dhaval Khandla

Hi Dhaval,

Thanks for your reply. I was going through the below provided documents 

https://software-dl.ti.com/mcu-plus-sdk/esd/AM64X/08_01_00_14/exports/docs/industrial_protocol_docs/am64x/ethercat_slave/plc_codesys.html

https://software-dl.ti.com/mcu-plus-sdk/esd/AM64X/08_01_00_14/exports/docs/industrial_protocol_docs/am64x/ethercat_slave/simple_demo_in_twincat3.html

If I understand correctly, the bare minimum hardware requirements for testing out an etherCAT connection are a PLC, a PC and am64x evm board.

Is there any way to test out etherCAT connection without involving a PLC(like using raspberyy Pi and slave device only)? This is because of the difficulty in acquiring one. 

Our ultimate goal is to exchange data packets between a master (PC) and slave (am64x). How can this be made possible. So far in the simple etherCAT slave example, i have not seen any data transfer APIs. Please do list out the APIs that implement this functionality.

Thank you.

Hi

Aaron Renny said:

Is there any way to test out etherCAT connection without involving a PLC(like using raspberyy Pi and slave device only)?

Yes, it is possible. EtherCAT Slave Setup with TwinCAT page explains how  to connect EtherCAT Slave running on AM64x with a TwinCAT master (running on PC). For these steps, you do not need any PLC.

Regards
Dhaval Khandla

Hi Dhaval,

The link given above doesnot seem to be working. Can you please check again. 

Also can you please list the APIs that provides data transfer between the master and slave and vice versa.

Also please do tell how this data transfer functionality can be implemented in the Simple etherCAT slave example.

Thank you

Hi

Aaron Renny said:

The link given above doesnot seem to be working. Can you please check again. 

Sorry about that. Here is the link : https://software-dl.ti.com/mcu-plus-sdk/esd/AM64X/08_01_00_14/exports/docs/industrial_protocol_docs/am64x/ethercat_slave/simple_demo_in_twincat3.html

Aaron Renny said:

Also can you please list the APIs that provides data transfer between the master and slave and vice versa.

Also please do tell how this data transfer functionality can be implemented in the Simple etherCAT slave example.

https://software-dl.ti.com/mcu-plus-sdk/esd/AM64X/08_01_00_14/exports/docs/industrial_protocol_docs/am64x/ethercat_slave/example1.html
Above page explains the flow of the simple example.

https://software-dl.ti.com/mcu-plus-sdk/esd/AM64X/08_01_00_14/exports/docs/industrial_protocol_docs/am64x/ethercat_slave/group___e_c___a_p_i___s_l_v.html
You can check the API documentation for more details about each API.

Regards
Dhaval Khandla

Hi Dhaval,

Thank you for the reply. I had gone through the simple etherCAT Slave Example.

Please correct me if i am wrong, my understanding is that the example just initialises the process data objects and doesnot actually send anything to the master.

Our goal is the send and recieve data  to and from the master by the slave. Is there any modification to be done to the Simple etherCAT Slave Example or is this functionality already available within the example. 

Please list out the steps realise and test out this functionality. 

Thank you.

Hi

Aaron Renny said:

Please correct me if i am wrong, my understanding is that the example just initialises the process data objects and doesnot actually send anything to the master.

The example also sets up the PRU-ICSSG on AM64x. It loads firmware on PRU cores of PRU-ICSSG, which acts as EtherCAT Slave Controller. So after running this example, if you send packets using master, the slave will process it. Also, in EtherCAT, there is not notion of slave sending a packet to master.

Aaron Renny said:

Please list out the steps realise and test out this functionality. 

To test the communication, you can follow the instructions for TwinCAT as mentioned in the previous reply.

Regards
Dhaval Khandla

Hello Aaron,

The example actually sends data from the master to the slave. In step 10 of "Scanning the slave" LEDs are controlled from the master. That's "Output" data in EtherCAT speak.

Data from the slave back to the master is referred to as Input in EtherCAT. Not sure if the simple example has any meaningful Input data defined.

Maybe some background helps:

Technically Inputs and Outputs are mostly transmitted using the same Ethernet packet (you could have multiple packets,but usually you don't), since every communication is always initiated by the master. When the packet passes the slave, outputs are read from the packet and inputs are put back into the packet (that's the magic behind EtherCAT - the packets are modified on the fly as they pass through the slave). At the end of the chain (EtherCAT networks always form a line topology, even if you have a more complex cabling topology with branches or even a star topology) the packet is sent back all the way to the master. On the way back, the packet isn't being looked at anymore for inputs and outputs.

Regards,

Dominic

Hi Dhaval,

Thanks for your reply. We are trying out different approaches to test out a simple communication from master to slave.

We just need to send a packet (suppose a string) from master to the slave and have the slave display it using some output port(eg: UART).

Can use list out the steps to make this possible. Also while going through the APIs provided, i found multiple APIs that fetch outputs like:

EC_API_SLV_getOutputData()

EC_API_SLV_PDO_getData()

EC_API_SLV_PDO_get()

EC_API_SLV_CBObjRead_t()

which of these APIs will help us to collect data send by the master. We are also looking at SOEM provided by openetherCAT society to act as a master.

Our goal is to just test out a basic communication that sends a data as simple as a string from the master to the slave and have the slave display it. Please list the steps in order to do this.

Thank you.

Hi Dominic,

Thanks for your reply. We are testing out a basic functionality in which the master sends a data as simple as a string, to the slave, and let the slave display this data using any interface. Can you tell me what kind of packets do the master send to the slave. I see a lot of words like object, record, variable and cannot figure out where exactly the data is stored.

Also please do mention any modifications required in the Simple etherCAT Slave code in order to capture data send by the master and display it.

Thank you. 

Hi

Aaron Renny said:

Our goal is to just test out a basic communication that sends a data as simple as a string from the master to the slave and have the slave display it. Please list the steps in order to do this.

If you check the "Scanning the slave" section in EtherCAT Slave Setup with TwinCAT page, we have i2c-leds present in one of the RxPDO. Using that, you can control few LEDs on EVM from TwinCAT.

And you can check "EC_SLV_APP_applicationRun()" function in "ecSlvSimple.c" file of the example, to see how the LEDs are being updated based on process data updates from master.

Regards
Dhaval Khandla

Hi Dhaval

Thanks for the reply. Please tell me how the data packets are send from the master to the slave. We just need to send a string from the master to slave and have the slave display it. Also mention the APIs related to reading data from the Master by the Slave.

Thank you.

Adding to the previous question, is there any other way of realising an EtherCAT master besides using TwinCAT. I am looking into SOEM master provided by the open EtherCAT society. Please do list out any alternate methods.

Thank you.

Any updates ?

Hi

Aaron Renny said:

Please tell me how the data packets are send from the master to the slav

That depends on the configurations you select on the master side. You can check the documentation for master you are using.

Aaron Renny said:

We just need to send a string from the master to slave and have the slave display it. Also mention the APIs related to reading data from the Master by the Slave.

https://software-dl.ti.com/mcu-plus-sdk/esd/AM64X/08_01_00_14/exports/docs/industrial_protocol_docs/am64x/ethercat_slave/example1.html

As mentioned earlier, this is one of the sample examples provided in the SDK. We have i2c-leds present in one of the RxPDO. Using that, you can control few LEDs on EVM from TwinCAT. You can modify the PDOs to the type and size of data needed in your application. "Process Data Object Configuration" section briefly explains how to modify it.

https://software-dl.ti.com/mcu-plus-sdk/esd/AM64X/08_01_00_14/exports/docs/industrial_protocol_docs/am64x/ethercat_slave/group___e_c___a_p_i___s_l_v.html
Complete stack API documentation is available here. But you can check the simple example to understand how and where to call which APIs.

Regards
Dhaval Khandla

Hi

Aaron Renny said:

Adding to the previous question, is there any other way of realising an EtherCAT master besides using TwinCAT. I am looking into SOEM master provided by the open EtherCAT society. Please do list out any alternate methods.

Apart from SOEM, you can check IgH if you want a Linux based solution, and Acontis is a commercially supported option. 

You can also see this video for more information : https://training.ti.com/ethercat-master-on-sitara-processors-acontis-codesys

Regards
Dhaval Khandla

Hi Dhaval,

Thank you for your reply. I was looking more into the ethercat protocol and found that there are many adressing modes available (Direct, logical etc).

I would like to know which all addressing modes does the am64x slave support. 

Also, please do list out the data types (int , float, char) that can be used in the etherCAT communication with the slave.

Thank you

Hi

Aaron Renny said:

Thank you for your reply. I was looking more into the ethercat protocol and found that there are many adressing modes available (Direct, logical etc).

I would like to know which all addressing modes does the am64x slave support.

https://software-dl.ti.com/mcu-plus-sdk/esd/AM64X/08_01_00_25/exports/docs/industrial_protocol_docs/am64x/ethercat_slave/ethercat_datasheet.html
As mentioned here, we support all EtherCAT Commands (NOP, APRD, APWR, APRW, FPRD, FPWR, FPRW, BRD, BWR, BRW, LRD, LWR, LRW, ARMW and FRMW). So you should be able to use different addressing modes.

Aaron Renny said:

Also, please do list out the data types (int , float, char) that can be used in the etherCAT communication with the slave.

You can refer this Application Note ET9300 (EtherCAT Slave Stack Code) for details. Chapter 7 is dedicated to objects.

Regards
Dhaval Khandla

Hi Dhaval,

Thank you for the reply. I would like to know how the master acquires the adress of the slave. Also how does the master set the slave adress. If my understanding is correct, both of these are different addressing schemes.

I would like to know how these actions are performed when the ESI file is not available to the master. 

Thank you

Hi
For more details on different addressing modes, please check the following document, if you have not seen it already.

https://download.beckhoff.com/download/Document/io/ethercat-development-products/ethercat_esc_datasheet_sec1_technology_2i3.pdf

And following one specifically talks about different master features: https://www.ethercat.org/download/documents/ETG1500_V1i0i2_D_R_MasterClasses.pdf

Regards
Dhaval Khandla