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MESC TOOL NEWS:
MESCT-NC30-971101D
NC30WA V.2.00 Release 1
NC30 V.2.00 Release 1
Precaution
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Please note the following errors concerning C compilers NC30 V. 2.00 Release 1 and NC30WA V.2.00 Release 1 (with assembler), used with the M16C/60 Series .
These errors will be corrected in the next upgraded version.
Immediate Value Right Shift
- Problem
When the operation result between a long-type variable and an immediate value
in the range of 0x8000L to 0xffffL is right-shifted, the result is an unsigned shift.
The result should be arithmetic shift when normal(MSB becomes "1"),
but the actual results in this case are logical shift (MSB becomes "0").
- Example
[C language source example]
long l,a;
l=(a+0x8000L)>>n;
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- Solution
Cast the constant with signed long.
[C language source example]
l=(a+(signed long)0x8000L) >> n;
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NC30WA V.2.00 Release 1, NC30 V.2.00 Release 1 Precaution
MESCT-NC30-971101D
Register Variable Tampering
- Occurrence Conditions
- "-fER" is specified as the compile option.
Note: "-fER" is the option which make register variable available.
- TMP variable, storing the register variable, is used in multiple "IF" or "FOR" branches.
Note: TMP variable is output by C compiler.
Tampering occurs when both of these conditions are satisfied at the same time.
- Error Example
[C language source example]
int func(int i){
register int k;
for(k=0;k<100;k++){
if(func2(i))
return k;
}
return 0;
}
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- Solution
Please do not use "-fER".
NC30WA V.2.00 Release 1, NC30 V.2.00 Release 1 Precaution
MESCT-NC30-971101D
Constant compare should be an unsigned operation, but occurs as a signed operation.
- Occurrence Conditions
- Comparison with an unsigned char type constant.
- Compare data is signed constant of 0x80 or greater.
- The variable compared with a constant is to be calculated.
- Error Example
[C language source example]
unsigned char c;
if(0x90<(c&0x0f))
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- Solution
Use the `U` specifier to define the constant as unsigned. (Ex: 0x90 --> 0x90U)
NC30WA V.2.00 Release 1, NC30 V.2.00 Release 1 Precaution
MESCT-NC30-971101D
When "-fSSU" is specified as the compile option, more stack data may be provided than in actual use.
- Occurrence Conditions
- Bit-field to bit-field transfer.
- Bit-field is int type.
- Both source and destination are registers, and they are different registers.(It is the matter of C compiler.)
- All registers are in use. (It depends on contents of user program)
- Solution
Do operation (transmission) after substituting source for temporary variable once.
NC30WA V.2.00 Release 1, NC30 V.2.00 Release 1 Precaution
MESCT-NC30-971101D
A system error may occur when "~" tilde operator is applied to bit data.
- Occurrence Conditions
- Source is AUTO type bit field.
- Source FB offset is not within the -32 to +32 range.
- Destination is result of bit operation
Note: When user designats "#pragma SBDATA" or "#pragma ADDRESS", C compiler outputs bit instructions.
- Source and destination are both 1-byte bit fields.
- Bit width of source and destination are both 1.
- Solution
Do operation (transmission) after substituting source for temporary variable once.
NC30WA V.2.00 Release 1, NC30 V.2.00 Release 1 Precaution
MESCT-NC30-971101D
4-bit to 4-bit transfer operation may give an unknown value.
- Occurrence Conditions
- Transferring bit field of 4 bits width to bit field of 4 bits width .
- Source and destination are both `far`.
- Source and destination are both registers.
- Source and destination are both R0L
- Source bit position is the first four bits.
- Destination bit position is the 4th bit.
This problem occurs when all the above conditions are satisfied at the same time.
- Solution
Do operation (transmission) after substituting source for temporary variable once.
NC30WA V.2.00 Release 1, NC30 V.2.00 Release 1 Precaution
MESCT-NC30-971101D
Shift-left operation may give an unknown value.
- Occurrence Conditions
- Shift count is not constant (Right operand is not constant).
- Shift result is converted to lower data type.
- Storage destination bit width <= shift count value < bit size of shift target
- Error Example
[C language source example]
char c;
int i,count=9;
c=i << count;
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- Solution
After storing the shift result into a temporary variable of the same size as the shift target, store it to the destination.
NC30WA V.2.00 Release 1, NC30 V.2.00 Release 1 Precaution
MESCT-NC30-971101D
When a register value is used in an if statement and the result of the if sentence is false, the register value becomes unknown.
- Occurrence Conditions
- A register variable is effective by specifying -fER ,
or a variable is assigned to the register by specifying an optimization option (-0, -0R, -0S)
- The register is used again at a statement which is called when the if statement is true.
- "stz" instruction is output by compiler.
- Error Example
[C language source example]
func(int i){
if(i==1)
i=2;
return i;
}
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- Solution
Describe asm(""); immediately after the if statement.
NC30WA V.2.00 Release 1, NC30 V.2.00 Release 1 Precaution
MESCT-NC30-971101D
An error occurs when there are multiple returns in the inline function.
- Error Example
[C language source example]
inline func()
{
int i;
if(i==1)
return 0;
else if(i==2)
return 2;
return 1;
}
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- Solution
Keep all returns in one place.
[C language source example]
inline func()
{
int i, j=1;
if(i==1)
j = 0;
else if(i==2)
j = 2;
return j;
}
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NC30WA V.2.00 Release 1, NC30 V.2.00 Release 1 Precaution
MESCT-NC30-971101D
A 1-bit bit test may return a wrong value.
- Occurrence Conditions
- 1-bit bit field is tested in an if statement.
- The bit field is char type.
- The bit field test is performed by pointer-relative.
- The bit field is assigned on either R0H or R1H register for this operation.
- Solution
Store the bit field to be tested in a temporary variable before the comparison.
NC30WA V.2.00 Release 1, NC30 V.2.00 Release 1 Precaution
MESCT-NC30-971101D
The -WEF (-Werror_file) option doesn't function during compile in the Windows95 version.
- Solution
Please don't use -WEF.
Instead, output the file using -Wstdout.
NC30WA V.2.00 Release 1, NC30 V.2.00 Release 1 Precaution
MESCT-NC30-971101D
The offset will deviate when the total of auto variables and the stack return value of register arguments is more than 128 bytes.
- Occurrence Conditions
- Optimization option (-OR, -OS, -O) is not specified.
- Stack return of register arguments of the function occurs.
- Total of auto variables and register arguments is more than 128 bytes.
- Error Example
[C language source example]
func(int i)
{
int ary[80];
:
func2();
ary[3];
}
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- Solution
Please use the register declaration for the register argument of the function and specify "-fER" as compile option.
Or, specify optimization option (-0, -0R, -0S).
NC30WA V.2.00 Release 1, NC30 V.2.00 Release 1 Precaution
MESCT-NC30-971101D
When reading an initialized union member, the initial value may be read even if the value has been modified.
- Occurrence Conditions
- Optimization option (-0, -0R, -0S) is specified.
- A member of the union is a structure or a union.
- After a member ("A") is initialized, a value is written to another member ("B").
- The first member ("A") is then called again.
- Error Example
[C language source example]
union u{
struct{
unsigned char lowData;
unsigned char highData;
}byte;
unsigned int word;
}
func()
{
union u ustemp;
int c;
ustemp.bute.highData=0x80;
ustemp.bute.lowData=0x11;
ustemp.word=4;
c=ustemp.byte.highData;
}
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- Solution
Please insert asm ("") after member initialization.
NC30WA V.2.00 Release 1, NC30 V.2.00 Release 1 Precaution
MESCT-NC30-971101D
The FB offset value of the auto variable may deviate when -Ostack_frame_align (-OFSA) is specified.
- Occurrence Conditions
- A char type auto variable is declared.
- The effective area of auto variable and those of other auto variables do not conflict.
- "-OSFA" is specified as the compile option.
- Error Example
[C language source example]
func()
{
char c;
int i;
i=c;
return i;
}
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- Solution
Please don't use -OSFA.
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