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</o:shapelayout></xml><![endif]--></head><body lang=EN-NZ link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US'>There aren’t any official standards (as far as I know) for how portability of floats works between machines with different endianness.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US'>Usually however (AFAIK) they follow the same swapping rules as integers, so typically the best approach is to receive the possibly-wrong-endian value into a byte array or integer variable (<b>never</b> a float variable), then apply the conditional byte swap as if it were an integer, then reinterpret the bit pattern as a float (via a pointer cast, not a value cast nor union). So the Etherlab macros should work fine for this purpose. (Note that some compilers prefer that you perform an intermediate cast from integer to byte array then to float, rather than going directly from integer to float.)<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US'>Usually this will do the trick, assuming that the master and slave use compatible definitions of how floating point are represented (while rare, there are some processors around that don’t use IEEE floats). The main thing is to never put data that might be byte-swapped into a float/double variable (not even temporarily), because you’ll run into trouble with special interpretation of particular bit patterns.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US'><o:p> </o:p></span></p><div style='border:none;border-left:solid blue 1.5pt;padding:0cm 0cm 0cm 4.0pt'><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'> Eshwar Lal [mailto:eshwarkhatri@gmail.com] <br><b>Sent:</b> Tuesday, 14 February 2017 06:06<br><b>To:</b> Gavin Lambert <gavin.lambert@compacsort.com><br><b>Subject:</b> Re: [etherlab-users] EtherCAT data size compatibility issue<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>Hi,<o:p></o:p></p><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Thanks for your response, yes there are macros available for 64 bit read/write in ecrt.h.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>one question, is it valid only for integer values or I could use them for floating point data types as well?<o:p></o:p></p></div></div><div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>On Fri, Feb 10, 2017 at 12:22 AM, Gavin Lambert <<a href="mailto:gavinl@compacsort.com" target="_blank">gavinl@compacsort.com</a>> wrote:<o:p></o:p></p><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>64-bit macros are already defined in ecrt.h, so just use them.</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>In general though, if you want to deal with other data sizes, have a look at how the macros are defined, and define your own versions. They’re just wrappers around standard conditional byte-swapping calculations.</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Data on EtherCAT is little-endian by convention (although occasionally a slave will do something different), so the byte-swapping is only needed if your master code might run on a big-endian processor.</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> </span><o:p></o:p></p><div style='border:none;border-left:solid blue 1.5pt;padding:0cm 0cm 0cm 4.0pt'><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'> Eshwar Lal<br><b>Sent:</b> Friday, 10 February 2017 02:26<br><b>To:</b> <a href="mailto:etherlab-users@etherlab.org" target="_blank">etherlab-users@etherlab.org</a><br><b>Subject:</b> [etherlab-users] EtherCAT data size compatibility issue</span><o:p></o:p></p></div></div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:9.5pt;color:#0B5394'>hello all,</span><o:p></o:p></p><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:9.5pt'> </span><o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:9.5pt;color:#0B5394'>I am using EtherCAT master with ESC FC1100 for performing HIL simulations, I am using ecrt.h api functions to send a receive data variables,</span><o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:9.5pt'> </span><o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:9.5pt;color:#0B5394'>EC_READ_U32 and EC_WRITE_U32, which support only 32bit unsigned values, however my process variable is 64bit in size.</span><o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:9.5pt'> </span><o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:9.5pt;color:#0B5394'>is there any possible solution to this problem? so that I can transfer the variables 64bit in size over etherCAT and perform calculation for my simulation or any other possible tip to convert the 64bit variable to 32bit just for transmit and receive purpose. Or a method to transfer and receive 64bit values over EtherCAT.<br><br>it would be great to hear a positive solution to rectify the issue.</span><o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:9.5pt'> </span><o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:9.5pt;color:#0B5394'>Note: I am using Linux kernel with RTAI.</span><o:p></o:p></p></div></div></div></div></div><p class=MsoNormal style='margin-bottom:12.0pt'><br>_______________________________________________<br>etherlab-users mailing list<br><a href="mailto:etherlab-users@etherlab.org">etherlab-users@etherlab.org</a><br><a href="http://lists.etherlab.org/mailman/listinfo/etherlab-users" target="_blank">http://lists.etherlab.org/mailman/listinfo/etherlab-users</a><o:p></o:p></p></blockquote></div><p class=MsoNormal><br><br clear=all><o:p></o:p></p><div><p class=MsoNormal><o:p> </o:p></p></div><p class=MsoNormal>-- <o:p></o:p></p><div><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Tahoma",sans-serif'>Best Regards<b>.</b></span><b><span style='font-size:13.5pt;font-family:"Tahoma",sans-serif'><br></span></b><span style='font-size:10.0pt;font-family:"Tahoma",sans-serif'>Eshwar Lal </span><o:p></o:p></p></div></div></div></div></div></body></html>