RT HAL Component using an externa library and API

Dear All,


I am currently trying to develop a Real Time HAL component for a USB hardware device. This component is required to receive the USB packets in Real Time and deliver them to the LinuxCNC application program.


The USB hardware device is a serial to USB converter boards based on FTDI chip ( www.ftdichip.com/Products/ICs/FT232R.htm) . The serial (RS232) side of this board is a laser distance sensor which continually outputting the measured distance as UART packets. FDTI FT232R board converts them to USB protocol. The FT232R is supplied with its Virtual COM Port drivers and also with relevant C libraries and API functions (they call D2XX API functions).


In the process, I have prepared a HAL component as it is described in the HAL manual. Put my C function code with necessary API calls and FTDI library definitions in the component’s funtion definition part and compiled it with HAL’s “comp” function. The compiler gave fatal error: “ftd2xx.h No such a file or directory.”


The PROBLEM is:

How can i use an external library (such as ftd2xx.h library for the USB device in my case) to create a REAL TIME HAL component (like encoder component) ?

Thanks & Regards

Hi

I am currently trying to develop a Real Time HAL component for a USB hardware device.

I am not familiar with the FTDI boards and drivers, but it appears that whilst the ftdi_sio module is a kernel module, the libraries to access the virtual com port it creates, are shared object userspace libraries.
So it looks like the kernel module already exists, you need to use the API to communicate with it.

Real time components are kernel modules.
The hardware access they have is limited and low level, they operate in different memory space to user programs and you cannot link them to userspace libraries.

I recently submitted a patch to the comp / halcompile program, so that you can more easily link to external libraries, without having to build from C source code, but that only works for userspace components.
www.linuxcnc.org/docs/devel/html/hal/comp.html#_options
option extra_link_args "…"

I have used USB/Serial links from userspace components quite a few times and they generally work well.

What you will not be able to rely upon is low latency in the USB port, it is fine for passing data, but trying to pass pulse streams to drive steppers etc will not be reliable.
That is why there are no USB driver boards like SmoothStepper in use with Linuxcnc.

Put my C function code with necessary API calls and FTDI library definitions in the component’s funtion definition part and compiled it with HAL’s “comp” function. The compiler gave fatal error: “ftd2xx.h No such a file or directory.”

ftd2xx.h is a header file not a library.
If it was in the same directory as the source, or in one of the standard paths pointed to in the include pathspec. it would be found

As far as I can tell the library is libftd2xx.so

Assuming you have installed it, you could include that into the link of a userspace component, with the extra link option
option extra_link_args "L/somedir -lftd2xx"

regards

Hi ArcEye

Thanks for your illuminating reply. I did it as an userspace component and it works perfectly .

Best Regards

Dear Andy,

We appreciate for your valuable info shared with us.
As we understand from your e-mail, it is not strongly recommended to use third-party libraries to create real-time HAL components in kernel space. Instead it is more feasible to use a user-space (which is managable by real-time kernel not to compromise the reliability of the real-time processes such as servo-loop etc.) for such components containing third-party ingredients.

As we look through the links that you have send which lists the RTAPI functions, we have seen some HOSTMOT2 functions and Mesa_UART HAL components for UART connectivity. Specifically, the hm2_uart_xxx functions that you have authored.
We have some sensors which continuously send the sensor values from their RS422/232 ports to the host (our PC with LinuxCNC application). We would like to capture those data with some real time HAL components (preferably in kernel space) since we really need to precisely pair them with encoder readings. That is, if the sensor value read is not correctly paired with the actual position data (i.e. encoder value), the results of the computation depending on those data pairs become unreliable/inaccurate.
The question is, are those HOSTMOT2 API calls and the Mesa_UART HAL components that you have created are Real Time kernel components? Can we use them? and How can we use them? Do you have any example for this?

Note: On our system, we use MESA 5i23 board and some other 7i33 and 7i37 boards for servos and encoder captures with digital input outputs.

Thanks for your helps,
Best regards,
Mehmet DURNA

In fact we need a reliable, up-to date data. So, if your mesa_uart HAL component is functional, we would like to try it. Our sensor send out the sensor value as ASCII characters each for its digits (ie. '0', '7', '0', '3', 0x0D for 7.03mm, 0x0D being the packet delimiter). We can try to implement a HAL component to parse this array if we could read the packets from the mesa_hal component.
Is your driver loads a UART protocol bitfile to MESA card? Is there any high level protocol implemented or the mesa_uart component receives bytes in raw from the port? Also, can we assign any pins of the 5i23 to UART Rx Tx? How can we do this? Should we use an FPGA configurator such as XILINX ISE for that?

Best regards,
Mehmet

If you tell me what pinout /FPGA card/daughtercards you are using, I can make bitfile
either tomorrow if I get a chance or by Monday.