Fastest way to start a program after a falling edge

Direct Digital Labs

Is there a faster way to execute code after any falling edge in ASM ? ·

This is what I came up with.

[color=#000000]Step1:                                      ;Loop until Low[/color]
[color=#000000]            SNB    RA.0                ;1 cycle (2 if skip)[/color]
[color=#000000]            JMP     Step3               ;3 cycles[/color]
[color=#000000]            JMP     Step2               ;3 cycles[/color]
 
[color=#000000]Step2:                                      ;Loop until High[/color]
[color=#000000]            SB       RA.0                ;1 cycle (2 if skip)[/color]
[color=#000000]            JMP     Step2               ;3 cycles[/color]
[color=#000000]            JMP     Step3               ;3 cycles[/color]
 
[color=#000000]Step3:                                      ;Loop until Low[/color]
[color=#000000]            SNB    RA.0                ;1 cycle (2 if skip)[/color]
[color=#000000]            JMP     Step3               ;3 cycles[/color]
[color=#000000]            JMP     @Main            ;4 cycles (on another page)
[/color]

-TRC

Bean

JB RA.0,$
JNB RA.0,$
JB RA.0,$
JMP @Main

Bean.

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"SX-Video·Module"·available from Parallax for only $28.95 http://www.parallax.com/detail.asp?product_id=30012

"SX-Video OSD module"·available from Parallax for only·$49.95 http://www.parallax.com/detail.asp?product_id=30015
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·

Nate

2 Clock cycles after high-to-low trans:



JB RA.0,· $
JNB RA.0,· $
JB RA.0,· $

(Main code here, no jump)





Nate

Direct Digital Labs

Nice, forgot about the current address pointer!
·
The code space is tight (very tight) so I had to spilt things up a bit. This is what I ended up with, which works fine·since there is 16 clock cycles·during the last high transition.

 jb ra.0,$
 jnb ra.0,$
 jmp @Start

  ORG $200

 
Start:
  jb SH2,$
 
Main:

Thanks for your help!

-Dan-

Bean

Nate said...

2 Clock cycles after high-to-low trans:

JB RA.0,· $
JNB RA.0,· $
JB RA.0,· $

(Main code here, no jump)

The fastest conditional loop on the SX is 4 cycles (as in JB RA.0, $), but if the transition occurs right after the bit test, it will be 5 cycles until the next instruction. 3 for the jump back, 1 for the bit test, and 1 for the skip.

Two cycles would be best case, 5 cycles worst case.

Bean.


▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"SX-Video·Module"·available from Parallax for only $28.95 http://www.parallax.com/detail.asp?product_id=30012

"SX-Video OSD module"·available from Parallax for only·$49.95 http://www.parallax.com/detail.asp?product_id=30015
Product web site: www.sxvm.com

Available now! Cheap 4-digit LED display with driver IC·www.hc4led.com

"I reject your reality, and substitute my own." Mythbusters
·

Peter Verkaik

And if an interrupt occurs,
worst case is 5 + intperiod cycles

regards peter
·