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FFT
Joined: 07 Jul 2010
Posts: 92
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| Why CCS generates large code |
 Posted: Wed Jul 07, 2010 3:19 pm |
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Hello,
I have a question that I could not find any answer.
I add the code part and its assembly output. How can I force CCS to compile smaller code? PIC is 12F675 and v4.107
| Code: |
#use delay(clock=4M,RESTART_WDT)
#byte gpio = getenv("SFR:GPIO")
#bit STX = gpio.5
#use fast_io(A)
int8 i;
int32 TheData=0xAA55;
.
.
.
for(i=0;i<18;i++)
{
if(bit_test(TheData,i))
STX=1;
else
STX=0;
delay_us(100);
STX=1;
delay_us(50);
STX=0;
delay_us(50);
} |
| Code: | .................... for(i=0;i<18;i++)
01D2: CLRF 2E
01D3: MOVF 2E,W
01D4: SUBLW 11
01D5: BTFSS 03.0
01D6: GOTO 203
.................... {
.................... if(bit_test(TheData,i))
01D7: MOVF 36,W
01D8: MOVWF 23
01D9: MOVF 35,W
01DA: MOVWF 22
01DB: MOVF 34,W
01DC: MOVWF 21
01DD: MOVF 33,W
01DE: MOVWF 20
01DF: MOVF 2E,W
01E0: MOVWF 37
01E1: BTFSC 03.2
01E2: GOTO 1EA
01E3: BCF 03.0
01E4: RRF 23,F
01E5: RRF 22,F
01E6: RRF 21,F
01E7: RRF 20,F
01E8: DECFSZ 37,F
01E9: GOTO 1E3
01EA: BTFSS 20.0
01EB: GOTO 1EE
.................... STX=1;
01EC: BSF 05.5
.................... else
01ED: GOTO 1EF
.................... STX=0;
01EE: BCF 05.5
.................... delay_us(100);
01EF: CLRWDT
01F0: MOVLW 20
01F1: MOVWF 20
01F2: DECFSZ 20,F
01F3: GOTO 1F2
01F4: GOTO 1F5
....................
.................... STX=1;
01F5: BSF 05.5
.................... delay_us(50);
01F6: CLRWDT
01F7: MOVLW 10
01F8: MOVWF 20
01F9: DECFSZ 20,F
01FA: GOTO 1F9
.................... STX=0;
01FB: BCF 05.5
.................... delay_us(50);
01FC: CLRWDT
01FD: MOVLW 10
01FE: MOVWF 20
01FF: DECFSZ 20,F
0200: GOTO 1FF
.................... }
0201: INCF 2E,F
0202: GOTO 1D3 |
Thanks |
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bkamen
Joined: 07 Jan 2004
Posts: 1611
Location: Central Illinois, USA
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| Posted: Wed Jul 07, 2010 3:23 pm |
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HA! you should see the output of some other compilers...
That looks pretty decent although others might have some suggestions -- most likely you'll have to write your own assembly..
But that looks pretty good.
-Ben
_________________
Dazed and confused? I don't think so. Just "plain lost" will do. :D |
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rnielsen
Joined: 23 Sep 2003
Posts: 852
Location: Utah
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| Posted: Wed Jul 07, 2010 5:00 pm |
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You need to remember that the device is an 8bit MCU and you are manipulating a 32bit variable. Just in the bit_test() routine, nine extra instructions are needed to manipulate this. Change it to an 8bit variable and you will get nine fewer instructions for that command.
Ronald |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Wed Jul 07, 2010 5:42 pm |
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Here is a version where you can keep the int32 and shave of 10 instructions: | Code: | for(i=0;i<18;i++)
{
STX = shift_right(&TheData, sizeof(TheData), 1);
delay_us(100);
STX=1;
delay_us(50);
STX=0;
delay_us(50);
} |
| Code: | .................... STX = shift_right(&TheData, sizeof(TheData), 1);
004E: BCF PMDATH.5
004F: BSF STATUS.C
0050: RRF TheData+3,F
0051: RRF TheData+2,F
0052: RRF TheData+1,F
0053: RRF TheData,F
0054: BTFSC STATUS.C
0055: BSF PMDATH.5
.................... delay_us(100);
|
It modifies the contents of TheData, but for many applications this is no problem.
And because you are only using 18 of the 32 bits, it can be reduced by 1 more instruction when you shift only 3 bytes (24 bits) instead of 4 bytes (32 bits).: | Code: | STX = shift_right( ((int8*) &TheData) + 1, 3, 1);
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Last edited by ckielstra on Wed Jul 07, 2010 5:55 pm; edited 1 time in total |
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FFT
Joined: 07 Jul 2010
Posts: 92
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| Posted: Wed Jul 07, 2010 5:47 pm |
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@rnielsen, yeah, I understand, but I have to have 18 bit data :(
@ckielstra,
But I'm sending first 18 bit of TheData and it's problem to be modified, right? |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Wed Jul 07, 2010 5:58 pm |
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| FFT wrote: | | But I'm sending first 18 bit of TheData and it's problem to be modified, right? |
From the small code fragment you have posted we can not see if this is a problem or not. It all depends on what you are doing with TheData variable after you have transmitted the contents. Most likely you are going to read new data from your sensor and then it doesn't matter. |
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