Hi, On Mon, 19 Oct 2015, Bo Berglund wrote:
> I am making a control program for a data collection system using FPC + > Lazarus on a Raspberry Pi2 platform. I will use a number of Delphi > units, which implement the communications and data handling needs in a > way that works fine on a Windows platform. > > While looking over existing code I see that there are instructions to > modify received data from the instrument by reversing the byte order. > The reason for that was that the instrument is based on a Motorola > controller and it uses the opposite byte order as in the Intel CPU:s > on the PC. Since download is of binary data areas in the instrument > the byte order change was necessary for all multi-byte data like word > and integers as well as real (floating point 32 bit values). > > Now I wonder if it will be necessary also on an ARM platform like the > RPi2? Yes. > Is there a function or such to interrogate the byte order of the > platform FPC runs on? So that I could add a test at the start of > download to check if swapping is needed? There are compile time defines. ENDIAN_LITTLE and ENDIAN_BIG. As documented here: http://www.freepascal.org/docs-html/prog/progap7.html But the Raspberry Pi2's ARM is little endian, just like the x86 processors in a PC. It's also pretty easy to write a test function, which determines it runtime: function islittleendian: boolean; var x: longint; begin x:=1; islittleendian:=pbyte(@x)^ = 1; end; This will return true on little endian processors, and false on big endians. Should return true on RPi2 and x86 PCs. > Or is the ARM used on RPi2 working with the same byte order as the > Motorola MC68HC11 MCU is? No, the MC68HC11 is big endian (according to the Internet, I have no direct experience with that platform). BTW, big endian is also known as "network byte order" so you could look at sockets unit, which has network-to-host and host-to-network byte order which will just "always work" so compile to a no-op on big endian platforms, while doing the right conversion on little endian ones. Charlie _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
