How do I define a data table in C18? - Electronic Circuits Projects Diagrams Free

blueroomelectronics · 14th April 2008, 07:47 PM

I'm still really new with C18 but here goes.

I would like to define a table for a IR remote transmitter in C18
The table would contain
IR KHz modulation, mark, space, mark, space,... ,0 (end)

mark and space are the IR on and off times in ms
0 = end of this data stream

Also I would like to know how to address multiple tables, can they be varying in length?
Lastly can I insert formula for some of the data and let the C18 compiler sort out the answer?

futz · 14th April 2008, 08:08 PM

Look up arrays in your C book. Look at structs too. A C guru will give you better answers than me though.

David / W9GF · 14th April 2008, 09:36 PM

Bill - could what i've pasted below be an example of what you are asking?

(Sorry - i'm a novice at this thing and don't know how to post code so it looks purdy)

David

// Define the structure of one table entry
typedef struct {
unsigned char mark;
unsigned char space;
// Add more stuff if you need it - bits, arrays or anything you want
} BILLSIRRemoteTableStructure;

// Define a Variable & initialize it that uses this structure

BILLSIRRemoteTableStructure iBillsTable[] = { // Initialize table with values
{1,20},
{2,40},
{3,50},
{0,0} // Mark End of data
};

void DoSomething(int mark, int space);

main()
{
int counter;

// Scans through table and does something with each value
// Not such a good example because it would also
// do something with the last value
for(counter=0;counter<sizeof(iBillsTable)/sizeof(BILLSIRRemoteTableStructure);++counter)
DoSomething(iBillsTable[counter].mark,iBillsTable[counter].space);

// Scans through table until sees a 0x00 for mark & space
for(counter=0;iBillsTable[counter].mark!=0 && iBillsTable[counter].space!=0;++counter)
DoSomething(iBillsTable[counter].mark,iBillsTable[counter].space);

}

void DoSomething(int xmark, int xspace)
{
return;
}

blueroomelectronics · 14th April 2008, 09:47 PM

Thanks, I'm an assembler guy trying to learn C. That gives me the framework I need.

futz · 15th April 2008, 12:41 AM

Quote:

Originally Posted by blueroomelectronics

Thanks, I'm an assembler guy trying to learn C. That gives me the framework I need.

BTW you can put static arrays in flash or eeprom. Thats what I did with my font for the GLCD. It was eatin up all the ram, and since it was never going to change (it's static) I told the compiler to put it in program memory.

Like this:

Code:

rom char *alpha1 = {
	0x3e,0x51,0x49,0x45,0x3e,	//0
	0x00,0x42,0x7f,0x40,0x00,	//1
	0x72,0x49,0x49,0x49,0x46,	//2
	0x22,0x49,0x49,0x49,0x36,	//3
	0x0f,0x08,0x08,0x7f,0x08,	//4
	0x2f,0x49,0x49,0x49,0x31,	//5
	0x3e,0x49,0x49,0x49,0x32,	//6
	0x41,0x21,0x11,0x09,0x07,	//7
	0x36,0x49,0x49,0x49,0x36,	//8
	0x26,0x49,0x49,0x49,0x3e};	//9

The "rom" tells the compiler that you want it stored in flash.

Mike, K8LH · 16th April 2008, 01:56 AM

Thank you Futz. Can you show me how you access a char in that const rom array please?

blueroomelectronics · 16th April 2008, 02:20 AM

Seems the answer is on page 53
http://www.kevin.org/frc/C18_2.4_getting_started.pdf

Mike, K8LH · 16th April 2008, 02:35 AM

Thanks Bill... That example from your DS51295E document doesn't seem to be in my DS51295F document... I guess I didn't realize there was that big a difference in document revisions...

blueroomelectronics · 16th April 2008, 02:56 AM

Hmm, is the F the newest? I found that one searching for C18 arrays.

Pommie · 16th April 2008, 02:58 AM

I couldn't work out how you would use that example either and the above pdf doesn't seem to answer the problem.

The pdf suggests it should be,

Code:

rom char alpha1[] = {
	0x3e,0x51,0x49,0x45,0x3e,	//0
	0x00,0x42,0x7f,0x40,0x00,	//1
	0x72,0x49,0x49,0x49,0x46,	//2
	0x22,0x49,0x49,0x49,0x36,	//3
	0x0f,0x08,0x08,0x7f,0x08,	//4
	0x2f,0x49,0x49,0x49,0x31,	//5
	0x3e,0x49,0x49,0x49,0x32,	//6
	0x41,0x21,0x11,0x09,0x07,	//7
	0x36,0x49,0x49,0x49,0x36,	//8
	0x26,0x49,0x49,0x49,0x3e};	//9

You can then do alpha1[3] etc to access it.

Mike.

blueroomelectronics · 16th April 2008, 03:08 AM

Is this not how it's done? Why the "return roots[val];"

Code:

#include <p18f452.h> /* for 'PRODL' declaration and 'ACCESS' macro */
/*
* Locate the read-only table in program memory at address 0x1000.
* 'romdata' is used for data, and 'code' is used for instructions.
*/
#pragma romdata ROOT_TABLE = 0x1000
#define TABLE_SIZE 100
const rom unsigned char roots[TABLE_SIZE] =
{ 0, 1, 1, 1, 2, 2, 2, 2, 2, 3,
3, 3, 3, 3, 3, 3, 4, 4, 4, 4,
4, 4, 4, 4, 4, 5, 5, 5, 5, 5,
5, 5, 5, 5, 5, 5, 6, 6, 6, 6,
6, 6, 6, 6, 6, 6, 6, 6, 6, 7,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
7, 7, 7, 7, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 9, 9, 9, 9, 9, 9, 9, 9, 9,
9, 9, 9, 9, 9, 9, 9, 9, 9, 9 };
/*
* Data in access ram does not require banking.
* When compiled with -Oa, these pragmas and the near qualifier may
* be removed.
*/
#pragma udata access MY_ACS_DATA
near unsigned char root, square;
#pragma udata /* continue allocating static data in non-access ram */
/*
* Returns the truncated root of the value.
*/
unsigned char get_root (int val)
{
return roots[val];
}
void main (void)
{
static int val;
for (val = 0; val < TABLE_SIZE; val++)
{
/* 'square' holds the greatest perfect square less than or
* equal to 'val' */
square = get_root (val);
}
}

futz · 16th April 2008, 03:09 AM

Quote:

Originally Posted by Mike, K8LH

Thank you Futz. Can you show me how you access a char in that const rom array please?

I see I left out the brackets!

It works anyway. Here's a couple lines of the working code:

Code:

for(stripe=0;stripe<5;stripe++)			//letter stripe loop
	{
		data_write(alpha1[index]);	//write letters
		index++;			//increment stripe pointer

The compiler didn't warn at all. Compiled clean. Go figure...

Pommie · 16th April 2008, 03:15 AM

Quote:

Originally Posted by futz

I see I left out the brackets!

You left out the brackets but you inserted a * which turns it into a pointer. If it would compile you would end up with the data somewhere in rom and a variable called alpha1 that held the address of the first byte. When I try to compile it I get 2 errors.

Edit, Futz, are you saying it worked with the rom char *alpha1 = { definition. If so, was alpha1 defined beforehand?

Mike.

futz · 16th April 2008, 03:16 AM

Ah, here it is. From the BoostC manual:

Quote:

Rom
Strings or arrays of data can be placed into program memory.
Such variables are declared using regular data types and rom storage specifier.
Such rom variables must be initialized within declaration:
rom char *text = "Test string"; // text with trailing zero
rom char *ptr = "\0x64\11\12"; // 4 bytes: 0x64, 0x0B, 0x0C, 0x00
rom char *data = { 0x64, 11, 12 }; // 3 data bytes: 0x64, 0x0B, 0x0C
Please keep in mind that the rom storage specifier has several limitations:
• rom can be used with char data types only;
• there is no implicit cast between rom and regular data types. Though BoostC
will not generate an explicit error for such a cast, it is expected that the
operand should be casted back to its original type.
If this is not done, the resulting code will behave unpredictably.
• a rom pointer is internally limited to 8-bits: the constant array size is thus
limited to 256 elements. This is coherent with smaller cores constraints;
• access to rom elements has to be done exclusively through the [] operators
and they cannot be referenced with substring pointer initialized at
runtime. Please keep in mind that rom variables must always and exclusively
be initialized within declaration;

So it's legal in BoostC, but maybe not in other compilers.

Pommie · 16th April 2008, 03:31 AM

Sorry, I was still on C18. I must get around to playing with boostC.

Mike.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar
Title	Starter	Forum	Replies	Latest
usart with pic	neelam29	Micro Controllers	19	18th July 2009 09:39 AM
Motor controller	Totally blank	Electronic Projects Design/Ideas/Reviews	9	16th January 2008 02:12 PM
18F4550 - PORTD inputs are shaky, even with internal pull up enabled	toodles	Micro Controllers	0	29th April 2007 03:05 AM
help me to describe this code	indie	Micro Controllers	0	18th June 2004 02:11 PM
An error in pic16f84a, why?	Zener_Diode	Micro Controllers	6	11th April 2004 03:55 AM

14th April 2008, 07:47 PM	#1
blueroomelectronics	How do I define a data table in C18? I'm still really new with C18 but here goes. I would like to define a table for a IR remote transmitter in C18 The table would contain IR KHz modulation, mark, space, mark, space,... ,0 (end) mark and space are the IR on and off times in ms 0 = end of this data stream Also I would like to know how to address multiple tables, can they be varying in length? Lastly can I insert formula for some of the data and let the C18 compiler sort out the answer? __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com/

14th April 2008, 08:08 PM	#2
futz	Look up arrays in your C book. Look at structs too. A C guru will give you better answers than me though. __________________ ========================= Futz's Microcontrollers & Robotics =========================

14th April 2008, 09:36 PM	#3
David / W9GF	C Data Structures in Array's Bill - could what i've pasted below be an example of what you are asking? (Sorry - i'm a novice at this thing and don't know how to post code so it looks purdy) David // Define the structure of one table entry typedef struct { unsigned char mark; unsigned char space; // Add more stuff if you need it - bits, arrays or anything you want } BILLSIRRemoteTableStructure; // Define a Variable & initialize it that uses this structure BILLSIRRemoteTableStructure iBillsTable[] = { // Initialize table with values {1,20}, {2,40}, {3,50}, {0,0} // Mark End of data }; void DoSomething(int mark, int space); main() { int counter; // Scans through table and does something with each value // Not such a good example because it would also // do something with the last value for(counter=0;counter<sizeof(iBillsTable)/sizeof(BILLSIRRemoteTableStructure);++counter) DoSomething(iBillsTable[counter].mark,iBillsTable[counter].space); // Scans through table until sees a 0x00 for mark & space for(counter=0;iBillsTable[counter].mark!=0 && iBillsTable[counter].space!=0;++counter) DoSomething(iBillsTable[counter].mark,iBillsTable[counter].space); } void DoSomething(int xmark, int xspace) { return; }

14th April 2008, 09:47 PM	#4
blueroomelectronics	Thanks, I'm an assembler guy trying to learn C. That gives me the framework I need. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com/

16th April 2008, 01:56 AM	#6
Mike, K8LH	Thank you Futz. Can you show me how you access a char in that const rom array please?

16th April 2008, 02:20 AM	#7
blueroomelectronics	Seems the answer is on page 53 http://www.kevin.org/frc/C18_2.4_getting_started.pdf __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com/

16th April 2008, 02:35 AM	#8
Mike, K8LH	Thanks Bill... That example from your DS51295E document doesn't seem to be in my DS51295F document... I guess I didn't realize there was that big a difference in document revisions...

16th April 2008, 02:56 AM	#9
blueroomelectronics	Hmm, is the F the newest? I found that one searching for C18 arrays. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com/

16th April 2008, 03:31 AM	#15
Pommie	Sorry, I was still on C18. I must get around to playing with boostC. Mike.