void pointer

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Read-Only Author techven khsl Posted 23-Dec-2004 11:41 GMT Toolset C51	void pointer techven khsl Hi, Any idea what does following do and how ? ((void (code *) (void)) 0) (); Any help would be great

Read-Only Author A.W. Neil Posted 23-Dec-2004 11:48 GMT Toolset C51	RE: void pointer A.W. Neil Apart from the Keil-specific 'code' keyword, it's standard 'C' - see your 'C' textbook. For the Keil-specific 'code' keyword, see the Keil C51 Manual.

Read-Only Author Jay Daniel Posted 23-Dec-2004 14:27 GMT Toolset C51	RE: void pointer Jay Daniel techven, It's still early, so spare me the tirade if I screw this up, but here goes: What this snippet of code is probably meant to do (in short form) is reset the processor (or at least jump code execution to address 0 so it can jump to the start of the application). Andy's right that this is all standard C, but just start from the 0 (the only value in the statement) and look at the casts. The value is cast to a pointer (in code memory, in this case) to a function returning void and taking no parameters (although the author put in an extra "void" for clarity). After this cast, the function at that location is "called" with the (); which will do what I described above.

Read-Only Author A.W. Neil Posted 23-Dec-2004 14:52 GMT Toolset C51	RE: void pointer A.W. Neil "What this snippet of code is probably meant to do (in short form) is reset the processor (or at least jump code execution to address 0 so it can jump to the start of the application)." As Jay so carefully says, that may be what it's meant to do; but note that jumping to code address 0x0000 is not the same thing as resetting the processor - by a long way. A true reset will reset the chip hardware and then restart the software from code address 0x0000. Simply jumping to code address 0x0000 will leave the chip hardware in an indeterminate state when the software restarts. If you need to do a reset, the best way is to use a watchdog and just let it time-out. There's been plenty of discussion of this - try a 'Search'

Read-Only Author Jay Daniel Posted 23-Dec-2004 15:02 GMT Toolset C51	RE: void pointer Jay Daniel I have to agree with Andy. Now that you know what this author was trying to do, the best thing for YOU to do is something entirely different. For instance, if this is done in an interrupt service routine, you're almost certainly going to have a screwed up system after this quasi-reset. And no matter where it's called from, you'll have to take care of the stack pointer, etc. to get things back to the correct state. The best way to reset will always be to turn on the watchdog and then just throw a while(1); in the code and wait for a proper reset.

Read-Only Author Dan Henry Posted 23-Dec-2004 15:27 GMT Toolset C51	RE: void pointer Dan Henry "... what this author was trying to do ..." Now this author needs to figure out what processor and toolchain he/she is dealing with. http://www.htsoft.com/forum/all/showflat.php/Cat/0/Number/15018/an/0/page/0#15018

Read-Only Author Jay Daniel Posted 23-Dec-2004 15:47 GMT Toolset C51	RE: void pointer Jay Daniel Hehe... good find Dan. It must be a bit galling to see a bunch of posts to the effect of "don't do what this hack is doing" when you wrote the code yourself. So it goes...

Read-Only Author Jon Ward Posted 23-Dec-2004 16:38 GMT Toolset C51	RE: void pointer Jon Ward I think there's a more interesting point in all of this. There are no replies on the HiTech forum except Dan's. There are six replies on the Keil forum. What meaning can we read into this? Software developers using HiTech tools are already celebrating Christmas and not answering forum questions? Software developers using Keil do not celebrate Christmas? HiTech developers are just now starting to shop for Christmas gifts and don't have time to answer forum queries? Keil developers are already celebrating Christmas, have already bought gifts, and after 15 minutes with the relatives are bored and have started web surfing? Either way, have a Merry Christmas. Jon

Read-Only Author Stefan Duncanson Posted 23-Dec-2004 16:56 GMT Toolset C51	RE: void pointer Stefan Duncanson Do you really celebrate Xmas in October?

Read-Only Author Dan Henry Posted 23-Dec-2004 17:14 GMT Toolset C51	RE: void pointer Dan Henry "What meaning can we read into this?" Corroborates the viewpoint favoring the 8051 in the 8051-vs-PIC market share debates?

Read-Only Author Keil Reinhard Posted 4-Jan-2005 17:17 GMT Toolset C51	RE: void pointer Keil Reinhard Even at Christmas time search at http://www.keil.com/support works. Entering "void code" gives several useful answers. Item 7 is: http://www.keil.com/support/docs/307.htm This perfectly answers the initial question.

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