Very useful indeed. Thanks Bob.

I programmed the table lookup method as well, this code is comparable in ti=
me. I like the calculus more than table lookup.

The minus sign in the addlw generates an error in my compiler, but I change=
d the signs so -9F =3D + x61. Did not test it in full yet, but it should wo=
rk.


What is OP?


Arjen



________________________________
Van: piclist-bounces@mit.edu <piclist-bounces@mit.edu> namens Bob Ammerman =
<picram@roadrunner.com>
Verzonden: vrijdag 11 augustus 2017 18:19
Aan: 'Microcontroller discussion list - Public.'
Onderwerp: RE: [PIC] pic16f628a memory bank switching in a large circular b=
uffer.

Here is an implementation of the OPs actual requirements, as I understand t=
hem. One of the neat things about this implementation is that the routines =
are isochronous, which means that they always take exactly the same amount =
of time.

Again, untested code!

-- Bob Ammerman
RAm Systems


Again, we have the two snippets of code already
defined, converted into macros

FIXINDEX:
Convert W from a number in the range 00h..9Fh into a number in one of the r=
anges 20h..6F or A0h..0EFh

BUMPINDEX
Increment W circularly, wrapping from 09Fh back to zero.

  ; INSP is the insertion pointer into
  ; the buffer. OFFSET is the number of
  ; samples 'back' in the buffer for output

  ;=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D
  ; INSERTION ROUTINE:

  MOVF  INSP,W
  FIXINDEX
  MOVWF FSR
  MOVF  INBYTE,W
  MOVWF INDF
  MOVF  INSP,W
  BUMPINDEX
  MOVWF INSP
  RETURN

  ;=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D
  ; OUTPUT ROUTINE

  ; Note: since INSP is pointer to
  ; one slot before the latest
  ; value, we want to subtract 1
  ; from the result of our sum of

  ; Convert the offset from
  ; a distance backward to
  ; a distance forward

  MOVWF OFFSET,W
  SUBLW 0

  ; Now compute the desired location
  ; in the buffer

  ADDWF INSP,W

  ; at this point we have to
  ; wrap any value greater
  ; than 09Fh. The next instruction
  ; will set carry if we have a sum
  ; greater then 9Fh.

  ADDLW 61H

  ; now we subtract 0A0h if we
  ; are over 9Fh. Note that we
  ; we use ADDLW instead of
  ; SUBLW because the latter
  ; computes 'literal minus W'
  ; rather than 'W minus literal',
  ; which is what we want.

  BTFSC STATUS,C
  ADDLW 100h-0A0h

  ; Finally subtract back out
  ; the 61H we added above. The
  ; same comment about ADDLW vs.
  ; SUBLW applies

  ADDLW 100h-061h

  ; Convert the value to a pointer
  ; and get the byte

  FIXINDEX
  MOVWF FSR
  MOVF  INDF,W

  ; Done!

  RETURN




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