#HIGH assembly operator problem

alfonso2Author

Visitor II

Posted on November 17, 2005 at 08:05

woro in this case the result is similary, but i need of the HIGH operator also in different asm codes for extracting the HIGH byte address of a variable.

ex.

unsigned short SMC_LOOKUP_TABLE[1024];

asm{

.....

....

ADD A,#HIGH(SMC_LOOKUP_TABLE)

}

[ This message was edited by: liotro78 on 17-11-2005 12:38 ]

alfonso2Author

Visitor II

Posted on November 17, 2005 at 08:11

excuse me woro but in lst file there is the c instruction pScan=&Buffer_0 and there isn't the asm translation....

why?

[ This message was edited by: liotro78 on 17-11-2005 12:54 ]

Visitor II

Posted on November 17, 2005 at 08:42

liotro78, I think that there is a workaround for the HIGH operator problem.

As far I can see, in your C program you can find the higher part of an address. You can also see C variables and symbols from the assembly.

Why do you not define a dummy variable, as:

const unsigned char Buffer_0H = HIGH(Buffer_0);

and use its value instead of the HIGH operator?

You can also tell the C compiler to put Buffer_0H in ROM, so no precious RAM byte is lost...

Regards

EtaPhi

alfonso2Author

Visitor II

Posted on November 17, 2005 at 09:00

ok EtaPhi

but i need of the address of high byte of buffer_0 and not of its value..

then if i do this code is correctly?

#define HIGH(x) ((x) >> 8)

const unsigned char Buffer_0H = HIGH(Buffer_0);

asm

{

LD A, #Buffer_0

LD pScan:1, A

LD A, #Buffer_0H //is similar to #HIGH(Buffer_0)????

LD pScan, A

}

[ This message was edited by: liotro78 on 17-11-2005 13:36 ]

Visitor II

Posted on November 17, 2005 at 09:09

What you wrote is not correct.

You must change

LD A,#Buffer_0H

with

LD A,Buffer_0H

because you need the content of Buffer_0H, not its lower address...

EtaPhi

alfonso2Author

Visitor II

Posted on November 17, 2005 at 09:22

But Buffer_0H content is an address?

Then if Buffer_0 is of this kind

volatile unsigned short Buffer_0[1024];

this code is always correct?

I need of a general definition of HIGH operator, that is good for all types of variable char,short etc...

Your HIGH define is good also if buffer_0 is an unsigned short array?

[ This message was edited by: liotro78 on 17-11-2005 14:09 ]

Visitor II

Posted on November 17, 2005 at 10:00

Yes, Buffer_0H contains the HIGH BYTE of Buffer_0 address (you set it in the initialization).

This workaround is also OK if Buffer_0 size changes or if it is moved somewhere else.

If you need the HIGH BYTE of another buffer (e.g. SMC_LOOKUP_TABLE), all you need is to define a new constant.

There is no limitation in the base-type of the buffer if you compute the right offsets, I mean: if you want to access the 3rd item of SMC_LOOKUP_TABLE whose items are 2 byte wide, you must add 6 to the address of SMC_LOOKUP_TABLE to access the high byte and you must add 7 to access the low byte.

EtaPhi

Visitor II

Posted on November 17, 2005 at 10:05

Ops, I made a mistake in my explanation!

The offset 6 and 7 are related to the 4th item...

EtaPhi

W

wolfgang2399

Visitor II

Posted on November 17, 2005 at 10:45

Hi liotro78,

mysterious!!!! My Metrowerks compiler (previous version) creates the expected list file

....

108: #pragma DATA_SEG NEAR RAM2

109: char Buffer_0[];

110: #pragma DATA_SEG SHORT BSCT

111: char* pScan;

112:

113: #pragma DATA_SEG DEFAULT

114:

115: void test(void)

116: {

117: pScan = Buffer_0;

0000 a600 LD A,#Buffer_0

0002 b701 LD pScan:1,A

0004 a601 LD A,#HIGH(Buffer_0)

0006 b700 LD pScan,A

118: };

0008 81 RET

....

I know, that's no great help. Sorry, I don't have any further idea.

Regards

WoRo