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Need to translate Libraries in C language to SCL

Created by: pavans at: 11/5/2014 3:50 PM (11 Replies)

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11/5/2014 3:50 PM	Rate (0)
pavans Posts: 81 Rating: (0)	Hello Friends, I need to translate libraries that were written for C to SCL, Please help me
pavans Posts: 81 Rating: (0)
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11/5/2014 3:55 PM	Rate (0)
0_Einstein Diamond Member Joined: 7/7/2010 Last visit: 11/19/2024 Posts: 15406 Rating: (2446)	pavans Hello Friends, I need to translate libraries that were written for C to SCL, Please help me What kind of help is it you are looking for? My first thought was to simply post "good luck" since there are many things you can do in C that are very hard in SCL or require a very different approach.
	science guy
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11/5/2014 4:06 PM	Rate (0)
William_B Posts: 5225 Rating: (1196)	Hi. For whatever it is worth.. SCL is close to PASCAL. If you change the format of the coding from C to PASCAL, you should already be okay. Remember though that SCL will not handle all PASCAL / C commands. If you are willing to post a sample piece I am sure we can already see where the dangers are and try and show you how to do the changeover. Greetings. w
William_B Posts: 5225 Rating: (1196)
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11/5/2014 6:10 PM	Rate (1)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 10/21/2024 Posts: 1547 Rating: (537)	As 'c' is entirely based on functions, you could just convert it on a function to function basis (1 to 1). Well from a simple data structure point-of-view the 2 languages are fairly analogous:- Structures - Present in both Unions - Can use the AT construct to mimic this Arrays - Present in both. 'c' is zero based so all array definitions in SCL would have to be [0..n] Pointers - This will be the biggest challenge. SCL does have pointers but they are nothing like as powerful as their 'c' equivalents. You would have to make these ANY pointers. Pointer initialisation (e.g. int ptr = MyInt;) would have to be replace by the runtime code ANYPtr := MyInt as static initailisation of pointers is not possible. Any pointer arithmatic such as ptr = ptr + 1, would have to be mimiced by manipulating the ANY address by the correct ammount (byte = 8, short = 16, long = 32). To do this you would have to have a dissambled ANY pointer to allow you to access the ANY pointer address data. There are many examples of this using code I have produced (e.g. https://www.automation.siemens.com/tf/WW/en/Posts/94234#top). Dereferencing the pointer to gain access to a value (e.g. i = ptr) would have to be replaced with BLKMOV calls. Pointers to structures (e.g. ptr->MyStruct) would be a nightmare to translate. You would have to point the ANY pointer at the base address of the structure and have offsets for the structure members that you add on before deferenecing the ANY pointer. Not nice as you would have to store them somewhere in a lookup table, and keep this updated with any changes to the structure. I suppose you could work out the address at runtime and them populate a lookup table (e.g. offset = element address - structure base address repeating for each element in the structure). As are the data types:- Signed char = CHAR in SCL Unsigned char = BYTE in SCL Signed short int (16 bit) = INT in SCL Unsigned short int (16 bit) = WORD in SCL Signed long int (32 bit) = DINT in SCL Unsigned long int (32 bit) = DWORD in SCL Float (single precision) = REAL in SCL Double (double precision) = not supported in SCL Variable scope maps quite well too. Auto variables = TEMP variables in SCL static variables = VAR variables in SCL The function argument list would translate to the function input, inout and output parameters and the function return would be equivalent to the c function return value. The RETURN instruction would be replaced thus:- RETURN (x / 10); ----> FCXXX := 10; RETURN; If I were doing it it would approach it thus:- 1) Make a note of any library / external functions that you call (e.g. strlen, strcpy etc.). Then write replacement functions that have the same call structure and return values. Then add code into the functions to mimic the library function it replaces. 2) Then start converting your user functions to equivalent SCL functions. Functions that do not have any static data can use an FC, whereby functions with static have to use an FB as FC'c have no static static capability. Just a few thoughts from a mad old programmer - but I hope they are of some help.
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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11/5/2014 6:48 PM	Rate (0)
0_Einstein Diamond Member Joined: 7/7/2010 Last visit: 11/19/2024 Posts: 15406 Rating: (2446)	smiffy and everyone else, I agree with what has been said. What has been omitted is what kind of C they are translating. It is something that loops or iterates through big chunks of data and post-processes? That's not good in a PLC and requires rethinking how to efficiently calculate a little every scan so that at the end of your data, you have a very small amount or none to calculate to arrive at a solution. Example: CRC calculation in C is basically looping, or post-processing (usually). In the real world in routers or real-time systems that use CRC, they do a little and very fast calculation with every chunk of data. Once they have all the data, they have arrived at the answer. By asking what type of problem they are attempting to solve, we can suggest numerical methods approaches that work in PLC programming that otherwise would cause watchdog faults and system halts. Yes, all the wonderful information presented is useful and may be all that the original poster needs. However, the next person to read this thread may not be aware of the similarities and the differences in a running C code on a PC and its equivalent in the PLC. I read library and immediately thought, well, check out oscat.de for the Library already written, and posted in these forums in SCL. Might save considerable amounts of time. But I asked first. Perhaps in these forums I should consider the relative slow bandwidth or infrequent logins from many users.
	science guy
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This contribution was helpful to 1 thankful Users Kahl

11/5/2014 7:37 PM	Rate (0)
William_B Posts: 5225 Rating: (1196)	@smiffy: Mad - maybe, but never old.. just experienced [wink] Brilliantly comprehensive answer you provided - thanks a 1,000,000. @huggy_d: "the next person to read this thread may not be aware of the similarities and the differences* in a running C code on a PC and its equivalent in the PLC"* Yeah buddy, that is my concern too. @pavans: Do you see what I meant.. putting your questions publically produces the best response. Hopefully the comments from smiffy will help. But please be aware of our cautions. The coding you wish to convert.. was it part of a micro-controller solution that you need to convert to PLC coding? Could you tell us which processor it is? PLEASE remember the PLC continuously cycle through the coding.. there is no "wait until something happens". You will need to adapt your philosophy to suit. BUT the most important thing is not converting the C coding.. the most important thing is to have a PLC system that has the same functionality. For example.. if there is some motion control involved I would recommend using internal control blocks that is available in the S7-1200. Just be careful for not loosing focus on what the real target is. Greetings. w
William_B Posts: 5225 Rating: (1196)
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11/5/2014 8:05 PM	Rate (0)
pavans Posts: 81 Rating: (0)	Thank you very much smiffy, huggy , williams for your support. I will explain you briefly what I need to convert to you. I am using T7-1-CAN inclinometer from usdigital to measure the angle of my solar panels, but the library files ( that has hex fromat protocol that estabishes communication with this T7-1-CAN) was written in C. So here is what I need to know I have .h file and .lib file of c program, So based on smiffy suggestion if i change all the commands in .h file file to SCL & uses tha same .lib file (because it have the hex commands that are assigned to C), Will it Work?? . If it works how can I add my .lib file to my project in Step 7 TIA portal V 13 Thanks everyone for your support Pavan
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11/5/2014 8:34 PM	Rate (0)
0_Einstein Diamond Member Joined: 7/7/2010 Last visit: 11/19/2024 Posts: 15406 Rating: (2446)	pavans Thank you very much smiffy, huggy , williams for your support. I will explain you briefly what I need to convert to you. I am using T7-1-CAN inclinometer from usdigital to measure the angle of my solar panels, but the library files ( that has hex fromat protocol that estabishes communication with this T7-1-CAN) was written in C. So here is what I need to know I have .h file and .lib file of c program, So based on smiffy suggestion if i change all the commands in .h file file to SCL & uses tha same .lib file (because it have the hex commands that are assigned to C), Will it Work?? . If it works how can I add my .lib file to my project in Step 7 TIA portal V 13 Thanks everyone for your support Pavan Since you are trying to track using a solar panel, why not instead look for a working solution to do just that? /tf/WW/en/Posts/56278 You can also contact your Siemens distributor for assistance locating a solar tracking setup that should take the inclinometer input, provided you convert to either rs485, rs232, or some other compatible interface for the s7-1200. Getting a CAN communications module may be a problem for the s7-1200 family. Am I right you are using the s7-1200 family for this project? And to answer your C library question, I am not aware of any S7-1200/1500 that would allow you to link with an external library file of the form you mention. The library files that work are basically offline storage of code snippets, hardware configurations, or even complete mini or starter projects store as a special library file. You would also need to translate the library source code. After reading what you are looking for, writing your own SCL code to accomplish the task would likely be a lot simpler, especially if you refer to your existing code as a guiding principles document rather than as a source code conversion task.
	science guy
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11/5/2014 11:26 PM	Rate (0)
pavans Posts: 81 Rating: (0)	Hello huggy Yes I am using s7 1200 -1214 CPU, I have a device from my Inclinometer Manufacturer to convert the CAN communiation to serial communication. So I am using RS 232 module along with my 1214 CPU to read the signal from the Inclinomter. Thanks, pavan
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11/6/2014 11:28 AM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 10/21/2024 Posts: 1547 Rating: (537)	pavans ...uses tha same .lib file (because it have the hex commands that are assigned to C), Will it Work?? . If it works how can I add my .lib file to my project in Step 7 TIA portal V 13 Absolutely no chance whatsoever. The libraries of which you speak are 'c' code libraries which contain object code that is pre-compiled for the target system (PC, UNIX box etc.) and is linked into the executable by the linker tool. The TIA portal will not be able to handle these files, and even if it did, you can't run code compiled for one CPU type on another CPU type. I agree with what others have said, that maybe you could take a step back. Ask yourself what you need to achieve at a specification level, rather than just blindly trying to port the 'c' code. As there maybe S7 blocks available that already have the same functionality as some of the 'c' code you are trying to port. It might work out quicker and easier in the long run to do it this way. I assume that you have a requirements / design specification for the original project?
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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