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maxneo
Joined: 07 Sep 2010
Posts: 35
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 Posted: Fri Jun 05, 2015 5:15 pm Post subject: optimize interrupt routine with Assembly |
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Can this code be done in a faster way as assemler and can anyone help me with it.
If Pinb.0 = 1 Then
Tccr1b.ices1 = 0
Else
Tccr1b.ices1 = 1
End If
Many thanks Felix
(BASCOM-AVR version : 2.0.7.8 ) |
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MWS
Joined: 22 Aug 2009
Posts: 1801
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| Posted: Fri Jun 05, 2015 7:40 pm Post subject: Re: optimize interrupt routine with Assembly |
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| maxneo wrote: | | Can this code be done in a faster way as assemler |
A bit, yes. But I doubt it will solve your problem.
| Quote: | | and can anyone help me with it. |
Show your own efforts and you may find help.
If you didn't start right now with asm, here's a most important document for Atmels:
http://www.atmel.com/Images/doc0856.pdf |
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Visovian
Joined: 31 Oct 2007
Posts: 584
Location: Czech
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| Posted: Sat Jun 06, 2015 6:46 am Post subject: |
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Bascom has translated your code like this: (for Mega16)
| Code: | //If Pinb.0 = 1 Then
SBIS PINB,0 ;Skip if bit in I/O register set
JMP L1 ;Jump
//Tccr1b.ices1 = 0
IN R23,TCCR1B ;In from I/O location
ANDI R23,0b10111111 ;Logical AND with immediate (clear bit R23.6)
OUT TCCR1B,R23 ;Out to I/O location
//Else
JMP L2 ;Jump
//Tccr1b.ices1 = 1
L1:
IN R23,TCCR1B ;In from I/O location
ORI R23,0b01000000 ;Logical OR with immediate (set bit R23.6)
OUT TCCR1B,R23 ;Out to I/O location
L2: |
I do not think it can be shorten/fasten. |
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MWS
Joined: 22 Aug 2009
Posts: 1801
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| Posted: Sat Jun 06, 2015 9:16 am Post subject: |
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| Visovian wrote: | | I do not think it can be shorten/fasten. |
You think wrong, it simply can be shortened and fastened by 1 or 2 cycles alone by using RJMP, the full address range of JMP isn't necessary here.
This is what it takes in cycles:
| Code: | SBIS 1/3
JMP 3
IN 1
ANDI 1
OUT 1
JMP 3
IN 1
ORI 1
OUT 1
' That's 7 or 9 cycles, depending on what branch is taken. |
| Code: | SBIS 1/2
RJMP 2
IN 1
ANDI 1
OUT 1
RJMP 2
IN 1
ORI 1
OUT 1
' Needs 6 or 7 cycles. |
| Code: | IN 1
ANDI 1
SBIS 1/2
ORI 1
OUT 1
' Takes constantly 5 cycles. |
Assuming no other bit of the timer configuration needs to be changed, one can use fixed values, IN/ANDI/ORI isn't required then:
| Code: | LDI 1
SBIS 1/2
LDI 1
OUT 1
' Needs 4 cycles |
But such small gain is all peanuts and effectively not the reason, which makes the code of the TO nonfunctional.
The bigger gain is achieved, in writing the complete ISR in ASM, as then it's possible to selectively save (PUSH/POP) only used registers, which gives a benefit of estimated 60-80 cycles, depending on the rest of the ISR-code.
As long there's still Basic code mixed with ASM in an ISR, it is much more difficult to save only the used registers.
As I've already stated, it is likely a different reason the TO's code http://www.mcselec.com/index2.php?option=com_forum&Itemid=59&page=viewtopic&t=12960 won't work.
It's not possible to give a sound assessment, only given chunks of code, so it's unlikely that the TO will get a more reasonable feedback.
That's also the reason I won't write sample ASM code for the TO, if he needs help, I expect him to do his part.
Which is at minimum that he shows some compilable code, which reflects his actual idea.
Everything else is wasted time.
Not that I'm not willing to waste time, but it's senseless wasted time. Big difference  |
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