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MESC TOOL NEWS:
MESCT-NC77WA-010316D
Please take note of the following problem in using C compiler NC77WA for the 77xx series of microcomputers.
- The x flag may not indicate correct status.
- Versions Concerned
NC77WA V.5.00 Release 1 -- V.5.20 Release 4
- Problem
In the processing that comes with backward jumps, the "for" statement for example, the x flag may not indicate correct status.
- 2.1 Conditions
- This problem occurs if the following four conditions are satisfied:
- (1) Data of type char and of other types co-exist within the range of backward jumps made with "goto" backward jumps only), "for", "while", or "do-while" statements (hereafter called a backward jump block).
- (2) In the first statement of the backward jump block in (1), a code that compares a constant with the contents of the X or Y register is generated by the compiler. (In Example below, the contents of register X is used as the offset value of s.ch1.)
- (3) In the last statement of the backward jump block in (1), a code that compares a constant of 0 with the contents of register X or Y is generated. (In Example below, the contents of register X is used as the offset value of uc[i].)
- (4) The program jumps to the beginning of the backward jump block with the X flag being set or cleared depending on the evaluation of the conditional expression in (3).
- 2.2 Example
-------------------------------------------------------------
/* In this example, the problem occurs
when compile option -OS used. */
struct S{
unsigned char ch1;
unsigned char ch2;
} s;
unsigned char uc[5];
void func(void)
{
int i, j;
for( i=0; i<2; i++ ){ /* Condition (1) */
if( s.ch1 == 1 ){ /* Condition (2) */
uc[i] = 1;
}
if( (uc[i] == 5) || (uc[i] == 0) ){ /* Condition (3) */
uc[i] = 0;
}
/* Condition (4)
* If evaluation TRUE, program jumps with X flag set to 1;
* otherwise, with X flag cleared to 0.
*/
}
}
-------------------------------------------------------------
- Workaround
If this problem arises, force the value of the X flag to change by adding an asm function immediately after the last backward jump block.
-
[Example]
-------------------------------------------------------------
struct S{
unsigned char ch1;
unsigned char ch2;
} s;
unsigned char uc[5];
void func(void)
{
int i, j;
for( i=0; i<2; i++ ){
if( s.ch1 == 1 ){
uc[i] = 1;
}
if( (uc[i] == 5) || (uc[i] == 0) ){
uc[i] = 0;
}
asm(2,0); /* Added to clear the X flag only to 0 */
}
}
-------------------------------------------------------------
- Schedule of Fixing Problem
We plan to fix this problem in our next release.
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