c_tips_and_tricks_for_pic_programming
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c_tips_and_tricks_for_pic_programming [2007/12/18 10:07] audiocommander added bitfields, cleaned up headline-levels |
c_tips_and_tricks_for_pic_programming [2009/01/05 18:21] Max Romantschuk Fixed broken structure |
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| </code> | </code> | ||
| * There's an excellent thread in the forum that discusses bitoperations: http://www.midibox.org/forum/index.php?topic=6981.0 | * There's an excellent thread in the forum that discusses bitoperations: http://www.midibox.org/forum/index.php?topic=6981.0 | ||
| + | * The [[http://www.midibox.org/forum/index.php/topic,9666.msg73781.html#msg73781|Re: Scan Matrix extended : VOIRINOV]] thread has an explanation of what the declaration of the bitfield is all about. | ||
| * If this is not enough, you could search for ASM optimized custom functions. You'll find some in code examples of TK, the [[ACSensorizer]] and a lot of PIC-Specialized Webpages – or of course the forum. | * If this is not enough, you could search for ASM optimized custom functions. You'll find some in code examples of TK, the [[ACSensorizer]] and a lot of PIC-Specialized Webpages – or of course the forum. | ||
| - | * If that still is not enough or you have no time and a lot of processing power / space available on your PIC, you can include the **libsdcc library**: | + | \\ |
| + | \\ | ||
| - | >> //if multiplications, divisions, pointer operations, etc. are used in the .c code, the linker may fail due to missing functions, which are part of the libsdcc.lib library. The common library for pic16 derivatives is not compatible to MIOS, therefore I've created a special one which can be downloaded from [[http://www.ucapps.de/mios/mios_libsdcc_v2_5_0.zip|here]]. Read the README.txt file for further details. [[http://www.ucapps.de/mios_c.html|TK on the C-Page]] // | + | ==== MIOS LIBSDCC Library ==== |
| + | |||
| + | If that still is not enough or you have no time and a lot of processing power / space available on your PIC, you can include the **libsdcc library**. Using the new MIOS GPUtils structure, this will be included automatically as required. | ||
| + | |||
| + | When using the library, sometimes the compiler will optimise multiplications to bitshifts (as demonstrated above) automatically. You can check the output files to see if this has occurred, but it is recommended to code the bitshifts manually, to be sure. | ||
| \\ | \\ | ||
| - | ====== Bitfields, Unions & Structs ====== | + | |
| + | ==== Bitfields, Unions & Structs ==== | ||
| * Avoid using huge int- or char-arrays when you just need to store some ON/OFF values. Use a bitfield instead | * Avoid using huge int- or char-arrays when you just need to store some ON/OFF values. Use a bitfield instead | ||
| Line 45: | Line 52: | ||
| // get number | // get number | ||
| mynum = something.ALL; | mynum = something.ALL; | ||
| + | |||
| </code> | </code> | ||
| - | >> // Due to an SDCC restriction, bitfields are limited to 8 bits max // | + | |
| + | >> It has been confirmed with recent versions of SDCC, that bitfields are not limited to 8bits as was previously expected. | ||
| - | \\ | ||
| ====== C Functions ====== | ====== C Functions ====== | ||
| Line 71: | Line 79: | ||
| * Adding the keyword '[[http://en.wikipedia.org/wiki/Volatile_variable|volatile]]' to a [[http://en.wikipedia.org/wiki/Variable|variable]] is a good idea when this variable can be changed or altered outside the sourcefile that declared this variable. | * Adding the keyword '[[http://en.wikipedia.org/wiki/Volatile_variable|volatile]]' to a [[http://en.wikipedia.org/wiki/Variable|variable]] is a good idea when this variable can be changed or altered outside the sourcefile that declared this variable. | ||
| - | * Always use 'unsigned' if you are sure you don't need negative values. As it's not clear how C treats a 'char' (signed: -128 to 127; unsigned: 0 to 255), it's better to be clear here. | + | * Always use 'unsigned' if you are sure you don't need negative values. Although the default is an unsigned char, it's not always clear how C treats a 'char' (signed: -128 to 127; unsigned: 0 to 255), so it's better to be clear here. |
| Line 96: | Line 104: | ||
| unsigned char value = MIDIValues[1]; //explicit temp variable | unsigned char value = MIDIValues[1]; //explicit temp variable | ||
| MIOS_MIDI_TxBufferPut(value); | MIOS_MIDI_TxBufferPut(value); | ||
| + | </code> | ||
| + | In most cases, adding parenthesis around your index variable has the same effect (see tip further down) | ||
| + | <code c> | ||
| + | MIOS_MIDI_TxBufferPut((MIDIValues[1])); | ||
| </code> | </code> | ||
| Line 101: | Line 113: | ||
| ==== Large Arrays ==== | ==== Large Arrays ==== | ||
| - | Arrays with more than 256 elements will produce compile (in fact linker) errors: | + | Arrays with more than 256 bytes of elements will produce compile (in fact linker) errors: |
| <code c> | <code c> | ||
| unsigned char myArray[256]; // will work | unsigned char myArray[256]; // will work | ||
| Line 108: | Line 120: | ||
| unsigned char myArray[64][4]; // will work | unsigned char myArray[64][4]; // will work | ||
| unsigned char myArray[64][5]; // will not be linked! | unsigned char myArray[64][5]; // will not be linked! | ||
| + | |||
| + | unsigned int myArray[128]; // will work | ||
| + | unsigned int myArray[129]; // will not be linked! | ||
| </code> | </code> | ||
c_tips_and_tricks_for_pic_programming.txt · Last modified: 2011/09/15 07:14 by ichaljhe
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