Recent changes to Atmega microsecond delay

Atmega microsecond delay modified by Mikael Nordman

Mikael Nordman — Thu, 13 Jan 2022 06:54:49 -0000

--- v2
+++ v3
@@ -1,4 +1,4 @@
-~~~~~
+~~~
 \ microseconds delay for Atmega
 -us
 marker -us
@@ -35,4 +35,4 @@

 decimal
 1000 us-cal
-~~~~~
+~~~

Atmega microsecond delay modified by Mikael Nordman

Mikael Nordman — Fri, 26 Dec 2014 08:03:24 -0000

--- v1
+++ v2
@@ -12,18 +12,15 @@
 \ clear watchdog
 : cwd [ wdr, ] ; inlined

-\ Clear watchdog (wdr instruction) takes one clock cycle
-\ Adjust the number of CWD to achieve a two us delay
-\ 6 CWD is needed for Atmega2560 @ 16MHz.
-\ 9 CWD is needed for Atmega328 @ 16MHz.
-\ NEXT execution time is longer on 2560 than on smaller chips
-\ The overhead of NEXT is too big for 1 us accuracy
-: 2us ( u -- ) \ busy wait for u times 2 microseconds
-  di 
-  for 
-   cwd cwd cwd cwd cwd cwd \ cwd cwd cwd
-  next
-  ei 
+\ Clear watchdog (wdr instruction) takes one clock cycle.
+\ Adjust the number of CWD to achieve a one us delay.
+\ 9 CWD is needed @ 16MHz.
+: us ( u -- ) \ busy wait for u microseconds
+  begin
+    cwd cwd cwd cwd cwd cwd cwd cwd cwd
+    1- dup 
+  0= until
+  drop 
 ;

 \ Helper word for calibrating the us loop
@@ -31,7 +28,7 @@
 marker -us-cal
 : us-cal ( u -- ) \ give target delay in ms
   ticks >r
-  for #500 2us next 
+  for #1000 us next 
   ticks r> - #1000 um* 
   cr d. ."  microseconds"
 ;

Atmega microsecond delay modified by Mikael Nordman

Mikael Nordman — Wed, 24 Dec 2014 09:14:18 -0000

\ microseconds delay for Atmega
-us
marker -us

\ Opcode only to flash
: op: ( opcode -- ) flash create , ram does> @ i, ;

\ Atmega wdr instruction
$95a8 op: wdr,

\ clear watchdog
: cwd [ wdr, ] ; inlined 

\ Clear watchdog (wdr instruction) takes one clock cycle
\ Adjust the number of CWD to achieve a two us delay
\ 6 CWD is needed for Atmega2560 @ 16MHz.
\ 9 CWD is needed for Atmega328 @ 16MHz.
\ NEXT execution time is longer on 2560 than on smaller chips
\ The overhead of NEXT is too big for 1 us accuracy
: 2us ( u -- ) \ busy wait for u times 2 microseconds
  di 
  for 
   cwd cwd cwd cwd cwd cwd \ cwd cwd cwd
  next
  ei 
;

\ Helper word for calibrating the us loop
-us-cal
marker -us-cal
: us-cal ( u -- ) \ give target delay in ms
  ticks >r
  for #500 2us next 
  ticks r> - #1000 um* 
  cr d. ."  microseconds"
;

decimal
1000 us-cal