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MESC TOOL NEWS:
MESCT-NC308WA-010116D
Please take note of the following problems in using C compiler with an assembler and integrated development environment NC308WA for the M16C/80 series of MCUs:
- On bitwise exclusive OR operations
- On "if" statements with expressions testing bit fields
- On multiplications of long or unsigned long type expressions
- On generating the MAX instruction
- Problem on Bitwise Exclusive OR operations
- 1.1 Version Concerned
- NC308WA V.3.10 Release 1
- 1.2 Description
- Compiling the C source file described a bitwise exclusive OR operation may result incorrect code being generated.
- 1.3 Conditions
- This problem occurs if the following three conditions are satisfied:
- (1) A bitwise exclusive OR operation is performed between a variable and a constant.
- (2) The constant in (1) is the nth power of 2 (n: an integer).
- (3) The result of the bitwise exclusive OR operation is stored in another variable.
- 1.4 Example
------------------------------------------------------------------
unsigned int a, b;
void func(void)
{
a = b ^ 0x0080; /* Conditions (1), (2), and (3):
0x0080 is the seventh power of 2 */
}
------------------------------------------------------------------
- 1.5 Workaround
- Use the same variable as the operand and the destination of a bitwise exclusive OR operation.
------------------------------------------------------------------
unsigned int a, b;
void func(void)
{
unsigned int t; /* Declares a temporary variable */
t = b;
t = t ^ 0x0080; /* The destination and the operand
of an operation are the same */
a = t;
}
------------------------------------------------------------------
- 1.6 Workaround
- We plan to fix this problem in our next release.
NC308WA Precaution
MESCT-NC308WA-010116D
- Problem on "if" Statements with Expressions Testing Bit Fields
- 2.1 Versions Concerned
- NC308WA V.3.00 Release 1 and V.3.10 Release 1
- 2.2 Description
- When an expression performing logical AND operations of bit fields are described in an if statement, incorrect code may be generated.
- 2.3 Conditions
- This problem occurs if the following ten conditions are satisfied simultaneously:
- (1) A single if statement or nested if statements are described.
- (2) A controlling expression in an if construct tests four bit fields.
- (3) All the bit fields in (2) are 1 bit wide each.
- (4) All the bit fields in (2) are contained in the same structure.
- (5) In the bit fields in (2), the low-order bit position has an offset of 0.
- (6) The bit fields in (2) are not assigned to continuous bit positions 0 through 3.
- (7) The following are used as expressions testing bit fields in (2), where "b" and "s" represent a bit field and the structure containing b respectively:
- (8) When two or more expressions testing bit fields exist in one controlling expression, they are all joined by the logical AND operator (&&).
- (9) The program is compiled using both the -O4 and the -OR options or the -O5 and the -OR options.
- (10) Option -ONLOC (-Ono_logical_or_combine) is not used.
- 2.4 Example
-----------------------------------------------------------------
struct bits {
char b0:1; /* Conditions (3), (4), (5), and (6) */
char b1:1;
char dummy:1; /* This field not used */
char b3:1;
char b4:1;
} s;
int i, j;
/* Condition (1): a single if statement */
void func1(void)
{
if (s.b0 && !s.b1 && (s.b3 == 1) && (s.b4 != 1)) {
/* Conditions (2), (7), and (8) */
i++;
}
j++;
}
/* Condition (1): nested if statements */
void func2(void)
{
if (s.b0 && !s.b1) { /* Conditions (2), (7), and (8) */
if (!s.b3 && s.b4) { /* Conditions (2), (7), and (8) */
i++;
}
}
j++;
}
-----------------------------------------------------------------
- 2.5 Workaround
- Use option -ONLOC (-Ono_logical_or_combine) at compilation.
- 2.6 Schedule of Fixing Problem
- We plan to fix this problem in our next release.
NC308WA Precaution
MESCT-NC308WA-010116D
- Problem on Multiplications of Long or Unsigned Long Type Expressions
- 3.1 Version Concerned
- NC308WA V.3.10 Release 1
- 3.2 Description
- When multiply operations of long or unsigned long type variables are described, System Error may arise at compilation.
- 3.3 Conditions
- This problem occurs if the following three conditions are satisfied:
- (1) Either or both of the operands in a multiplication are expressions of type long.
- (2) Either or both of the operands in a multiplication are not plain variables but expressions with operations (including implicit type conversion).
- (3) Option -OS is used.
- 3.4 Examples
------------------------------------------------------------------
long l, m;
char c;
void func(void)
{
l = c * l; /* Example 1: Conditions (1) and (2)
(implicit type conversion) */
m = m * (l + 1); /* Example 2: Conditions (1) and (2) */
}
------------------------------------------------------------------
- 3.5 Workaround
- Temporarily assign the expression used as an operand in a multiplication to a variable of type long; then, perform the multiply operation using this variable.
------------------------------------------------------------------
long l, m;
char c;
void func(void)
{
long t;
t = (long)c; /* Circumvents Example 1 */
l = t * l;
t = l + 1; /* Circumvents Example 2 */
m = m * t;
}
------------------------------------------------------------------
- 3.6 Schedule of Fixing Problem
- We plan to fix this problem in our next release.
NC308WA Precaution
MESCT-NC308WA-010116D
- Problem on Generating the MAX instruction
- 4.1 Version Concerned
- NC308WA V.3.10 Release 1
- 4.2 Description
- When a MAX instruction is generated, unnecessary comma is output, which may cause an assemble error.
- 4.3 Conditions
- This problem occurs if the following five conditions are satisfied:
- (1) The controlling expression in the if construct is the one that compares two variables by using relational operator "<" or ">".
- (2) The type of two variables in (1) is signed char or short (int).
- (3) The program statement executed if the controlling expression of the if statement in (1) is TRUE is only an assignment of the larger variable to the smaller one.
- (4) The result of the assignment in (3) is stored in a register.
- (5) Any one or more of the optimizing options -O, -O[1-5], -OR, and -OS are used for compilation.
- 4.4 Example
------------------------------------------------------------------
int j; /* Condition (2) */
int func(int i) /* Condition (2) */
{
if (i < j) /* Condition (1) */
i = j; /* Condition (3) */
return i;
}
------------------------------------------------------------------
- 4.5 Workaround
- Place asm(); immediately before the expression that is executed if the controlling expression is TRUE.
----------------------------------------------------------
if (i < j) {
asm();
i = j;
}
----------------------------------------------------------
- 4.6 Schedule of Fixing Problem
- We plan to fix this problem in our next release.
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