asking for the fastest way to toggle one bit in a register

Log in or register to post comments
Go To Last Post
7 posts / 0 new
Author
Message
darthvader
darthvader's picture
Level: Resident
Joined: Mon. Jul 18, 2005
Posts: 803 View posts
#1
Posted by darthvader: Sun. Jan 1, 2006 - 05:36 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi,
I use Mega128L and I want to toggle COM1C0 in TCCR1A, and I wrote:

if ((TCCR1A & _BV(COM1C0)) == 0x00)
{
TCCR1A |= _BV(COM1C0);
}
else
{
TCCR1A &= ~(_BV(COM1C0));
}

but it just take too many clock cycles, so I want faster code.
anyone have good idea?

Tags:

AVR Microcontrollers, megaAVR and tinyAVR
Top
bobgardner
bobgardner's picture
Level: 10k+ Postman
Joined: Wed. Sep 4, 2002
Posts: 26667 View posts
Location: Orlando Florida
Posted by bobgardner: Sun. Jan 1, 2006 - 06:03 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

TCCR1A ^= COM1C0; //flip bit 4 in reg

Imagecraft compiler user

Top
rstahlhu
rstahlhu's picture
Level: Posting Freak
Joined: Sat. Jun 8, 2002
Posts: 1242 View posts
Location: Champaign, IL USA
Posted by rstahlhu: Sun. Jan 1, 2006 - 06:06 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Use the exclusive OR function.

Try TCCR1A ^= _BV(COM1C0); I think ^ is the symbol for exclusive OR. Double check. This should flip the specified bit

Randy

Top
Pinkpanter
Pinkpanter's picture
Level: Hangaround
Joined: Mon. May 6, 2002
Posts: 124 View posts
Location: Netherlands
Posted by Pinkpanter: Sun. Jan 1, 2006 - 06:07 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I do not know what the _BV does try to make _BV(COM1C0) 0b0001 or something.
Or try looking at the assebmly code and try to make it faster in assembly.

But if you want to toggle this bit every time than try this
TCCR1A ^= _BV(COM1C0)

How many clock cycles does the code take any way?????

Top
darthvader
darthvader's picture
Level: Resident
Joined: Mon. Jul 18, 2005
Posts: 803 View posts
Posted by darthvader: Sun. Jan 1, 2006 - 06:07 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks, guys

Top
Koshchi
Koshchi's picture
Level: 10k+ Postman
Joined: Wed. Nov 17, 2004
Posts: 15674 View posts
Location: Vancouver, BC
Posted by Koshchi: Sun. Jan 1, 2006 - 10:00 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Doesn't anybody who hangs out at these forums do anything besides hang out at these forums?

Three virtually identical simultaneous answers!! LOL

Regards,
Steve A.

The Board helps those that help themselves.

Top
bobgardner
bobgardner's picture
Level: 10k+ Postman
Joined: Wed. Sep 4, 2002
Posts: 26667 View posts
Location: Orlando Florida
Posted by bobgardner: Sun. Jan 1, 2006 - 10:03 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I'm trying to rack up points for dropping a real tough stumper that no one can answer.

Imagecraft compiler user

Top