RE: Robby, __int8 limited to: -128 to 127.
- From: Robby <Robby@xxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Wed, 12 Dec 2007 17:07:01 -0800
Hello all!
I deeply appologize if I have caused such a confusion! But its really not my
fault nor is it yours!
The integer is 8 bits unsigned. In this compiler, if I want a 16 bit I have
to declare it as a 16 bit long variable.
And yes an 8bit int cannot hold a value of 256. CCS is currently working on
the issue.
My innitial code works fine without pointers. But with pointers the logic
should be the same.
As for the fellows that believe that my code is wrong, well, let me explain
myself.
Here's the original code. Now skip down to the explainations part under this
code.
=====================================Calling routine!
int spiA0=1,spiA1=0,spiA2=0;
//INCREMENT_ADDRESS BY AMOUNT OF INCREMENTATIONS REQUIRED
INC_ADDR(16,&spiA2, &spiA1,&spiA0);
=========================================Function!
void INC_ADDR( //***INCREMENT_ADDRESS***
int INCBY, //AMOUNT OF INCREMENTATIONS REQUIRED
int *A2, //MSB OF MESSAGE ADDRESS IN PAR FLASH
int *A1, //MIDSB OF MESSAGE ADDRESS IN PAR FLASH
int *A0) //LSB OF MESSAGE ADDRESS IN PAR FLASH
{
int i;
for(i=0;i<INCBY;i++)
{
if((*A0)==255) //Before A0 turns to 0, statement is true
{(*A1)++; //Increment central byte of flash adress
if((*A1)==255) //Before A1 to 0, statement is true
{ (*A2)++;//Increment MSBYTE of flash adress
} }
(*A0)++;
}}
=================================================
Look, its like this:
In order to access the data from my external memory I need a three byte
address comming out of my Micro controller. This is because I am creating my
own electronic computer hardware architecture. Therefore I have a
microcontroller connected to an external flash memory.
So suppose I need to access the data at address 000001 Hex from my flash.
Therefore byte1,byte2 and byte3 must look like this:
BYTE3 0000 0000 BYTE2 0000 0000 BYTE1 0000 0001
In my code spiA0 is BYTE1, spiA1 is BYTE2 and spiA2 is BYTE3
So if my code starts and fetches data from the memory at location
000001 Hex as innitialized in my code above (see spiA0, spiA1,spiA2 above!)
The three bytes are outputted to the memory address of the flash and my
controller retreives the pertinant 8 bit data via another 8 bit bus.
Then later say I want to access location 000002HEX of the memory. I call
INC_ADDR as so:
INC_ADDR(1,&spiA2, &spiA1,&spiA0);
Note this time the first parameter is a 1 instead of a 16! This mean we will
increment the 3 byte address by 1.
Once in the INC_ADDR function, the contents of the for loop is executed.
Lets look at what will happen when the first command in the code will be
executed.
if((*A0)==255) //Before A0 turns to 0 (at255), statement is true
Here, A0 is 1 right. So logic will skip the logic in the "if" statement and
will go straight to the:
(*A0)++;
and increment the A0 value from 1 to 2.
When the INC_ADDR function returns, then I can access data from location
000002HEX of the memory.
As this scenario goes on, and I keep calling the INC_ADDR function in order
to increment my 3 byte address, eventually, there will be a call where A0
will equal to 255, right! We do agree that when A0 is 255 and we call upon
INC_ADDR, its because we were at 0000FFHEX and we now require require
000100H. Right!
Once in the INC_ADDR function, the contents of the for loop is executed.
This time around lets look at what will happen when the first command in the
code will be executed.
In this instance, A0 is 255 right. So logic within the "if" statement will
be executed. As shown below: (Please view comments)!
for(i=0;i<INCBY;i++)
{
if((*A0)==255) //A0 is 255, so lets go increment A1!
{(*A1)++; //Increment A1!
if((*A1)==255) //Did A1 reach 255, if no then leave A2 alone!
{ (*A2)++;//Increment A2
} }
(*A0)++; //Increment A0 or wrap A0 back to 0
A1 will be incremented, A2 will be left alone and as the last command, A0 is
incremented, but since it was at 255, it will be reset to 0, Hence the
required address:
BYTE3 0000 0000 BYTE2 0000 0001 BYTE1 0000 0000
or
000100HEX
Once the function returns I access data at location 000100HEX of flash! The
same logic is applied for A2.
This logic works for this particular requirement and is probably not the
most efficient way to do this. I will later look into other possibilities as
suggested by Norbert to avoid unecessary looping in the case I would want to
increase my address from say 000001 to 00FFFF.
However in this case, I don't understand why I would worry about postfix and
prefixes on the variables. I always thought that prefix and postfix were
important when using lines like this:
int x;
x = ++(*A0);
or
x = (*A0)++;
I don't know why suggestions are made where I should use "++*A1;" as opposed
to "*A1++;" . I mean what difference would this make in my current logic
described above.
I have been using this fragment of code and aquired amazing results in this
microcomputer system.
Okay, its getting late, I have to run... sorry for the long post, I don't
mean to bore anyone with my silly memories and logic.
All feedback appreciated from all.
I thankyou all very much for your post, I sincerely appreciate it.
Cheers and happy holidays!
--
Best regards
Robert
"Jeff☠Relf" wrote:
Are you ( Robby ) asking about the contents of A1, the __int8 ?.
or A1 the pointer ? What does “ sizeof( int * ) ” return ?
If it's the __int8 ( i.e. “ sizeof( int ) == 1 ” )
then it can't be 256, as it's limited to: -128 to 127.
If it's the pointer you're talking about,
then you have to tell us what it's value was before entering the loop.
- Follow-Ups:
- Re: Robby, __int8 limited to: -128 to 127.
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- Robert, try: “ if ( * A1 ++ == 255 ) ++ * A2 ; ”.
- From: Jeff☠Relf
- Re: Robby, __int8 limited to: -128 to 127.
- References:
- Pointers gone mad!
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- Robby, __int8 limited to: -128 to 127.
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