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RENESAS TOOL NEWS on August 1, 2006 060801/tn2
| A Note on Using the C Compiler Packages
--M3T-NC308WA and M3T-NC30WA--
for the M16C MCU Family
--On Address Calculations
Made in an Iteration Statement-- |
Please take note of the following problem in using the C compiler packages
--M3T-NC308WA and M3T-NC30WA--for the M16C MCU family:
- On address calculations made in an iteration statement
- Products and Versions Concerned
- The M3T-NC308WA V.1.00 Release 1 through V.5.40 Release 00
(the C compiler package for the M32C/90, M32C/80, and M16C/80 series)
- The M3T-NC30WA V.1.00 Release 1 through V.5.40 Release 00A
(the C compiler package for the M16C/60, M16C/30, M16C/20, M16C/10, M16C/Tiny, and R8C/Tiny series
- Description
When address calculations are made in an iteration statement, incorrect results will be yielded if the increment of the loop counter is greater than one.
- Conditions
This problem occurs if the following conditions are all satisfied:
| (1) |
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In the program exists such an iteration statement as "for" or "while". |
| (2) |
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The loop counter is of type signed int, unsigned int, signed short or unsigned short. |
| (3) |
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The increment of the loop counter is greater than one. |
| (4) |
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In an iteration statement exists such an address calculation that references an array)
Here, the array is any one of these types, signed int, unsigned int, signed short and unsigned short. |
| (5) |
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The controlling expression in an iteration statement performs a comparison with a constant expression. |
| (6) |
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The variables used in the loop counter and for address calculations are those whose domains have been reserved in the stack frame. |
| (7) |
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The optimizing option -OS or -OS_MAX(-OSM) is used. |
Example:
------------------------------------------------
unsigned char buf[]; /* Condition (4) */
unsigned char *p;
for ( i=0; i<2; i+=2 ) { /* Conditions (1), (2), (3), and (5) */
p = buf + i*2; /* Condition (4) */
*p=0x00;
}
------------------------------------------------
- Workaround
Place a dummy asm function within the iteration statement.
Example:
------------------------------------------------
unsigned char buf[];
unsigned char *p;
for ( i=0; i<2; i+=2 ) {
asm()I; /* Dummy asm function placed */
p = buf + i*2;
*p=0x00;
}
------------------------------------------------
- Schedule of Fixing the Problem
We plan to fix this problem in the next release of the products.
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