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Reading T7

Elliot Chisholm

Hi

The code generated when I read the value of sfr T7 is as follows.

   178:                         start_time = T7 ;
00005C98 F2FE50F0  MOV      R14,DPP3:0x3050
   179:                         _nop_() ;

I would like it to be
MOV   R14,T7

What compiler options do I need to set to generate this ?

Cheers

Elliot

Parents
  • 0 in reply to Jon Ward

    Hi Jon,

    You are absolutely right. I must admit, I made a mistake. I got confused at first because in the C166 instruction set there is the instruction MOV Rn,Rm: F0nm. But the 4-bit addressing mode can't be used for T7, so this instruction wouldn't work here.
    But I would like to point out a different inefficiency in C166. Try compiling this code:

    unsigned long l;
unsigned int i;
void main(void)
{
    i = (unsigned int)(l >> 16) + 1;
}
    the compiler generates:
    0000 F2F50200 R    MOV       R5,l+02H
0004 F045          MOV       R4,R5   ; <- unnecessary
0006 0841          ADD       R4,#01H
0008 F6F40400 R    MOV       i,R4
000C CB00          RET
    Looks like the optimizer fails to eliminate unnecessary loading into temporary storage, which would seem a very basic type of optimization.

    - mike

Reply
  • 0 in reply to Jon Ward

    Hi Jon,

    You are absolutely right. I must admit, I made a mistake. I got confused at first because in the C166 instruction set there is the instruction MOV Rn,Rm: F0nm. But the 4-bit addressing mode can't be used for T7, so this instruction wouldn't work here.
    But I would like to point out a different inefficiency in C166. Try compiling this code:

    unsigned long l;
unsigned int i;
void main(void)
{
    i = (unsigned int)(l >> 16) + 1;
}
    the compiler generates:
    0000 F2F50200 R    MOV       R5,l+02H
0004 F045          MOV       R4,R5   ; <- unnecessary
0006 0841          ADD       R4,#01H
0008 F6F40400 R    MOV       i,R4
000C CB00          RET
    Looks like the optimizer fails to eliminate unnecessary loading into temporary storage, which would seem a very basic type of optimization.

    - mike

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