Speed optimization (framebuffer scrolling)

[HenrikOlsson]

I'm working on my MAX7219 display code and I'm in optimization mode. Have managed to get from 22ms to 6.5ms for redrawing a screen of 81 matrices (at 2MHz SPI clock) and I don't think I can squeeze more performance out of that particular section of the code at this moment. Next in line is the scrolling of the framebuffer, here's the code for it:

NumberOfDisplays  CON 36
FrameBufferSize   CON NumberOfDisplays * 10 + 20 

FrameBuffer       VAR BYTE[FrameBufferSize]
Row               VAR BYTE
Col               VAR WORD
Offset            VAR WORD
FrameBufferByte   VAR BYTE
MAX7219_Value     VAR BYTE


ScrollLeft:
    ' Shifts content of the screenbuffer one column to the left. It does not redraw the display.
    ' Input: None
    ' Output: None    
    ' This version: 3.5ms for 36 displays @64MHz

    FOR Col = 0 to NumberOfDisplays + 1                        ' 8 columns on left and right side, outside of display area
        For Row = 0 to 9                                                   ' One invisible row top and bottom of display area to facilitate vertical scrolling
            Offset = Row * (NumberOfDisplays + 2) + Col 
            MAX7219_Value = FrameBuffer[Offset] >> 1

            ' As long as the next byte is NOT the last byte in the row:
            IF Col < (NumberOfDisplays + 1) THEN
              FrameBufferByte = FrameBuffer[Offset + 1]
              MAX7219_Value.7 = FrameBufferByte.0
            ENDIF

            FrameBuffer[Offset] = MAX7219_Value
        NEXT
    NEXT
RETURN

Any ideas on how to make this run faster?

[tumbleweed]

Without getting into asm or anything, how about this (untested):

OFFSET_INCR CON NumberOfDisplays + 2
ScrollLeft:
    ' Shifts content of the screenbuffer one column to the left. It does not redraw the display.
    ' Input: None
    ' Output: None    
    ' This version: 1.30ms for 36 displays @64MHz

    ' do for Col < NumberOfDisplays+1
    FOR Col = 0 to NumberOfDisplays                        ' 8 columns on left and right side, outside of display area
        Offset = Col
        For Row = 0 to 9                                                   ' One invisible row top and bottom of display area to facilitate vertical scrolling
            'Offset = Row * (NumberOfDisplays + 2) + Col 
            MAX7219_Value = FrameBuffer[Offset] >> 1

            FrameBufferByte = FrameBuffer[Offset + 1]
            MAX7219_Value.7 = FrameBufferByte.0

            FrameBuffer[Offset] = MAX7219_Value
            Offset = Offset + OFFSET_INCR           ' basically Row * (NumberOfDisplays + 2)
        NEXT
    NEXT

    Col = NumberOfDisplays + 1                        ' 8 columns on left and right side, outside of display area
    Offset = Col
    For Row = 0 to 9                                                   ' One invisible row top and bottom of display area to facilitate vertical scrolling
        'Offset = Row * (NumberOfDisplays + 2) + Col 
        MAX7219_Value = FrameBuffer[Offset] >> 1
        FrameBuffer[Offset] = MAX7219_Value
        Offset = Offset + OFFSET_INCR           ' basically Row * (NumberOfDisplays + 2)
    NEXT
RETURN

That cuts it down to 1.3ms

[richard]

try some asm

untested but should be close
bcnt var byte bank 1
dcnt var byte bank 1
dspbuff var byte[380] ;36 displays + 2 outside of display * 10

rotate_r:  ' pic18
asm
    banksel _bcnt    ;ROW
    movlw   10       ;10 rows  
    movwf   _bcnt
    clrf    FSR0H
    movlw   low  (_dspbuff)
    movwf   FSR0L
    movlw   111        ;BUFFER SIZE low byte  (380-1) 36 displays + 2 outside of display * 10-1
    ADDWF   FSR0L,F
    movlw   high (_dspbuff)
    ADDWFC   FSR0H
    movlw   1        ;BUFFER SIZE high byte  (380)
    ADDWF   FSR0H
    banksel _bcnt     ;note place bcnt and dcnt in same bank
    MOVLW 38     ;36 displays + 2 outside of display  
NROW       
    movwf   _dcnt
    bcf    STATUS, C
Ncol
    rrcf   POSTDEC0 ,f     ;PER COLUMN
    DECFSZ  _dcnt ,F
    BRA    Ncol
    BNC    NBNC
    bsf    PLUSW0,7     ;max displays would be 127 to use plusw
NBNC 
    DECFSZ  _bcnt ,F
    BRA    NROW
    banksel 0
endasm

this is my 4 panel code for reference

rotate: ;pic18
asm
    banksel _bcnt    ;ROW
    movlw   8
    movwf   _bcnt
    clrf    FSR0H
    movlw   low  (_dspbuff)
    movwf   FSR0L
    movlw   31        ;BUFFER SIZE
    ADDWF   FSR0L,F
    movlw   high (_dspbuff)
    ADDWFC   FSR0H
    banksel _bcnt
    MOVLW 4
NROW     
    bcf    STATUS, C
    rrcf   POSTDEC0 ,f     ;PER COLUMN
    rrcf   POSTDEC0 ,f     ;PER COLUMN
    rrcf   POSTDEC0 ,f     ;PER COLUMN
    rrcf   POSTDEC0 ,f     ;PER COLUMN
    BNC    NBNC
    bsf    PLUSW0,7
NBNC 
    DECFSZ  _bcnt ,F
    BRA    NROW
endasm

[HenrikOlsson]

Richard, thank you. My problem is I suck as ASM and I don't understand half of what's going on there. It might very well work, in which case I'd be lucky but if it doesn't or I need to modify it I basically have no idea what I'm doing. I should use it as a learning exercise though as I do feel the need to better understand ASM.

tumblweed, wow, that was an easy yet effective modification (and it works perfectly fine) - just what I was hoping for.
Went down from 7.6ms to just above 3ms for a 81 matrix wide display. More than double the speed, cool!

One thing threw me off on a tangent for a while...

OFFSET_INCR CON NumberOfDisplays + 2

Since NumberOfDisplays is already a CONstant (with the value 81 in this particular case) I replaced

Offset = Offset + OFFSET_INCR

with

Offset = Offset + NumberOfDisplays + 2

expecting the compiler to replace both versions to

Offset = Offset + 83

It did not...your version with, the constant defined executes at 3.03ms, the other one in 3.45ms

I took 15 minutes for the penny to drop and now I need to go thru my code and see where else I've made that silly mistake.

Thanks again, both of you guys!

/Henrik.

[richard]

I should use it as a learning exercise though as I do feel the need to better understand ASM.

its worth the effort

this just under 100uS for a iteration

'****************************************************************
'*  Name    : UNTITLED.BAS                                      *
'*  Author  : richard                                           *
'*  Notice  : Copyright (c) 2022 caveat emptor                  *
'*          : All Rights Reserved                               *
'*  Date    : 11/10/2022                                        *
'*  Version : 1.0                                               *
'*  Notes   :                                                   *
'*          :                                                   *
'****************************************************************
#CONFIG
  CONFIG  FOSC = INTIO67
  CONFIG  PLLCFG = ON
  CONFIG  PRICLKEN = ON
  CONFIG  FCMEN = OFF
  CONFIG  IESO = OFF
  CONFIG  PWRTEN = ON
  CONFIG  BOREN = SBORDIS
  CONFIG  BORV = 190
  CONFIG  WDTEN = OFF
  CONFIG  WDTPS = 32768
  CONFIG  CCP2MX = PORTC1
  CONFIG  PBADEN = OFF
  CONFIG  CCP3MX = PORTB5
  CONFIG  T3CMX = PORTC0
  CONFIG  HFOFST = ON
  CONFIG  P2BMX = PORTB5
  CONFIG  MCLRE = EXTMCLR
  CONFIG  STVREN = ON
  CONFIG  LVP = OFF
  CONFIG  XINST = OFF
  CONFIG  DEBUG = OFF
  CONFIG  CP0 = OFF
  CONFIG  CP1 = OFF
  CONFIG  CP2 = OFF
  CONFIG  CP3 = OFF
  CONFIG  CPB = OFF
  CONFIG  CPD = OFF
  CONFIG  WRT0 = OFF
  CONFIG  WRT1 = OFF
  CONFIG  WRT2 = OFF
  CONFIG  WRT3 = OFF
  CONFIG  WRTC = OFF
  CONFIG  WRTB = OFF
  CONFIG  WRTD = OFF
  CONFIG  EBTR0 = OFF
  CONFIG  EBTR1 = OFF
  CONFIG  EBTR2 = OFF
  CONFIG  EBTR3 = OFF
  CONFIG  EBTRB = OFF
#ENDCONFIG
    




    DEFINE OSC 64
    DEFINE DEBUG_REG PORTB
    DEFINE DEBUG_BIT 7
    DEFINE DEBUG_BAUD 9600
    DEFINE DEBUG_MODE 0
    LATB.7=1
    bcnt       VAR BYTE   bank0
    dcnt       VAR BYTE   bank0
    BUFF       VAR BYTE[32]
    iteration  VAR word 
    OSCCON=$70
    OSCTUNE.6=1
    while ! osccon2.7 :WEND    ;wait for pll
    ANSELB=0
    ANSELC=0
    ANSELA=0 
    dspbuff var byte[380]
    clear
    trisc = %01111111 
    TRISB = %01111111
    TRISA = %11111111
    pause 1000
    debug 13,10,"ready",13,10
     LATc.7=0
     ;38x8 bits wide 10 bits high
     dspbuff[379]=$c0
     dspbuff[37]=$c0
main:
LATc.7=1; trigger oscilloscope
gosub rotate_r    
LATc.7=0
debug 13,10,dec iteration
debug 13,10,bin8 dspbuff[379]," " ,bin8 dspbuff[378]," " ,bin8 dspbuff[343] ," ",bin8 dspbuff[342] 
debug 13,10,bin8 dspbuff[37] ," " ,bin8 dspbuff[36] ," " ,bin8 dspbuff[1]   ," ",bin8 dspbuff[0] 
pause 200
iteration=iteration+1    
goto main    
    
    
    
    
rotate_r:  ' pic18    100uS
asm
    banksel _bcnt    ;ROW
    movlw   10       ;10 rows  
    movwf   _bcnt
    movlw   high (_dspbuff)
    movwf   FSR0H    
    movlw   low  (_dspbuff)
    movwf   FSR0L
    movlw   123        ;BUFFER SIZE low byte  (380-1) 36 displays + 2 outside of display * 10-1
    ADDWF   FSR0L 
    movlw   1        ;BUFFER SIZE high byte  (380)
    ADDWFC   FSR0H
    MOVLW 38     ;36 displays + 2 outside of display 
NROW  
    movwf   _dcnt
    bcf    STATUS, C
Ncol
    rrcf   POSTDEC0 ,f     ;PER COLUMN
    DECFSZ  _dcnt ,F
    BRA    Ncol
    BNC    NBNC
    bsf    PLUSW0,7     ;max displays would be 127 to use plusw
NBNC 
    DECFSZ  _bcnt ,F
    BRA    NROW
    banksel 0
    return
endasm

[HenrikOlsson]

Thanks Richard,
What device did you run this on?
After being unseccessfull in integrating your version into my code I tried to get your code (I removed some oscillator specific stuff to match my device) to compile for the 57Q43 but it won't.
It can't fit bcnt/dcnt into bank 0 so I tried various banks. Bank 5 works but I still get [ASM WARNING: ASM-SCROLL.ASM (411) : Invalid RAM location specified]

Line 411 in the .asm listing is banksel 0 in the NBNC routine.

I know it says warning and not error but the description sounds bad enough :-)

See, this is what I mean....

For reference, here's what I'm trying to compile for the 57Q43:

DEFINE OSC 64
DEFINE DEBUG_REG PORTB
DEFINE DEBUG_BIT 7
DEFINE DEBUG_BAUD 9600
DEFINE DEBUG_MODE 0

LATB.7=1

bcnt       VAR BYTE   bank0
dcnt       VAR BYTE   bank0
iteration  VAR word 

ANSELB=0
ANSELC=0
ANSELA=0 
dspbuff var byte[380]
clear
trisc = %01111111 
TRISB = %01111111
TRISA = %11111111
pause 1000
debug 13,10,"ready",13,10
 LATc.7=0
 ;38x8 bits wide 10 bits high
 dspbuff[379]=$c0
 dspbuff[37]=$c0


main:
LATc.7=1; trigger oscilloscope
gosub rotate_r    
LATc.7=0
debug 13,10,dec iteration
debug 13,10,bin8 dspbuff[379]," " ,bin8 dspbuff[378]," " ,bin8 dspbuff[343] ," ",bin8 dspbuff[342] 
debug 13,10,bin8 dspbuff[37] ," " ,bin8 dspbuff[36] ," " ,bin8 dspbuff[1]   ," ",bin8 dspbuff[0] 
pause 200
iteration=iteration+1    
goto main    
    
    
rotate_r:  ' pic18    100uS
asm
    banksel _bcnt    ;ROW
    movlw   10       ;10 rows  
    movwf   _bcnt
    movlw   high (_dspbuff)
    movwf   FSR0H    
    movlw   low  (_dspbuff)
    movwf   FSR0L
    movlw   123        ;BUFFER SIZE low byte  (380-1) 36 displays + 2 outside of display * 10-1
    ADDWF   FSR0L 
    movlw   1        ;BUFFER SIZE high byte  (380)
    ADDWFC   FSR0H
    MOVLW 38     ;36 displays + 2 outside of display 
NROW  
    movwf   _dcnt
    bcf    STATUS, C
Ncol
    rrcf   POSTDEC0 ,f     ;PER COLUMN
    DECFSZ  _dcnt ,F
    BRA    Ncol
    BNC    NBNC
    bsf    PLUSW0,7     ;max displays would be 127 to use plusw
NBNC 
    DECFSZ  _bcnt ,F
    BRA    NROW
    banksel 0
    return
endasm

[richard]

18f26k22

i have not tried much with Q43 yet , but
they have no ram below bank 5.
i dont know what bank pbp defaults to for them bank0 makes no sense at all , before them pbp kinda assumes bank0 before and after calls.
the instruction set is slightly different. movfffl or whatever
there may be other weird shit with indirect addressing

i have some q43's i just lack the enthusiasm to learn about them when the tried and trusty k22 serves my needs

[richard]

try them in bank6
and just remove the banksel 0 at the end


i added a rotate left to and a few tweaks

'****************************************************************'*  Name    : UNTITLED.BAS                                      *
'*  Author  : richard                                           *
'*  Notice  : Copyright (c) 2022 caveat emptor                  *
'*          : All Rights Reserved                               *
'*  Date    : 11/10/2022                                        *
'*  Version : 1.0                                               *
'*  Notes   :                                                   *
'*          : pic18f26k22                                                  *
'****************************************************************
#CONFIG
  CONFIG  FOSC = INTIO67
  CONFIG  PLLCFG = ON
  CONFIG  PRICLKEN = ON
  CONFIG  FCMEN = OFF
  CONFIG  IESO = OFF
  CONFIG  PWRTEN = ON
  CONFIG  BOREN = SBORDIS
  CONFIG  BORV = 190
  CONFIG  WDTEN = OFF
  CONFIG  WDTPS = 32768
  CONFIG  CCP2MX = PORTC1
  CONFIG  PBADEN = OFF
  CONFIG  CCP3MX = PORTB5
  CONFIG  T3CMX = PORTC0
  CONFIG  HFOFST = ON
  CONFIG  P2BMX = PORTB5
  CONFIG  MCLRE = EXTMCLR
  CONFIG  STVREN = ON
  CONFIG  LVP = OFF
  CONFIG  XINST = OFF
  CONFIG  DEBUG = OFF
  CONFIG  CP0 = OFF
  CONFIG  CP1 = OFF
  CONFIG  CP2 = OFF
  CONFIG  CP3 = OFF
  CONFIG  CPB = OFF
  CONFIG  CPD = OFF
  CONFIG  WRT0 = OFF
  CONFIG  WRT1 = OFF
  CONFIG  WRT2 = OFF
  CONFIG  WRT3 = OFF
  CONFIG  WRTC = OFF
  CONFIG  WRTB = OFF
  CONFIG  WRTD = OFF
  CONFIG  EBTR0 = OFF
  CONFIG  EBTR1 = OFF
  CONFIG  EBTR2 = OFF
  CONFIG  EBTR3 = OFF
  CONFIG  EBTRB = OFF
#ENDCONFIG
    


    NumberOfDisplays  CON 36
    NumberOfRows  CON 10
    DEFINE OSC 64
    DEFINE DEBUG_REG PORTB
    DEFINE DEBUG_BIT 7
    DEFINE DEBUG_BAUD 9600
    DEFINE DEBUG_MODE 0
    LATB.7=1
    bcnt       VAR BYTE   bank0
    dcnt       VAR BYTE   bank0
    BUFF       VAR BYTE[32]
    iteration  VAR word 
    OSCCON=$70
    OSCTUNE.6=1
    while ! osccon2.7 :WEND    ;wait for pll
    ANSELB=0
    ANSELC=0
    ANSELA=0 
    dspbuff var byte[380]
    clear
    trisc = %01111111 
    TRISB = %01111111
    TRISA = %11111111
    pause 1000
    debug 13,10,"ready",13,10
    LATc.7=0
    ;38x8 bits wide 10 bits high


main:
    iteration=0
    dspbuff[379]=3
    dspbuff[37]=3
    WHILE  iteration<610
        LATc.7=1
        gosub rotate_l
        LATc.7=0
        debug 13,10,dec iteration
        debug 13,10,bin8 dspbuff[379]," " ,bin8 dspbuff[378]," " ,bin8 dspbuff[343] ," ",bin8 dspbuff[342] 
        debug 13,10,bin8 dspbuff[37] ," " ,bin8 dspbuff[36] ," " ,bin8 dspbuff[1]   ," ",bin8 dspbuff[0] 
        pause 50
        iteration=iteration+1 
    WEND
    iteration=0
    dspbuff[379]=$c0
    dspbuff[37]=$c0
    WHILE  iteration<610
        LATc.7=1
        gosub rotate_R
        LATc.7=0
        debug 13,10,dec iteration
        debug 13,10,bin8 dspbuff[379]," " ,bin8 dspbuff[378]," " ,bin8 dspbuff[343] ," ",bin8 dspbuff[342] 
        debug 13,10,bin8 dspbuff[37] ," " ,bin8 dspbuff[36] ," " ,bin8 dspbuff[1]   ," ",bin8 dspbuff[0] 
        pause 50
        iteration=iteration+1 
    WEND
goto main    
    
    
    
    
rotate_r:  ' pic18
asm
    banksel _bcnt  ;ROW
    movlw   _NumberOfRows    ;10 rows  
    movwf   _bcnt
    movlw   high (_dspbuff)  ;BOTTOM OF BUFFER
    movwf   FSR0H    
    movlw   low  (_dspbuff)
    movwf   FSR0L
    movlw   low((_NumberOfDisplays + 2)*_NumberOfRows-1) ;TOP OF BUFFER
    ADDWF   FSR0L 
    movlw   high((_NumberOfDisplays + 2)*_NumberOfRows-1)    
    ADDWFC  FSR0H
    MOVLW   _NumberOfDisplays + 2;36 displays + 2 outside of display 
RROW  
    movwf   _dcnt        ;display
    bcf     STATUS, C
Rcol
    rrcf    POSTDEC0 ,f  ;PER display
    DECFSZ  _dcnt ,F
    BRA     Rcol
    BNC     RBNC
    bsf     PLUSW0,7     ;max displays would be 127 to use plusw
RBNC 
    DECFSZ  _bcnt ,F
    BRA     RROW
    banksel 0
    return
endasm
 rotate_l:  ' pic18
asm
    banksel _bcnt              ;ROW
    movlw   _NumberOfRows 
    movwf   _bcnt
    movlw   high (_dspbuff)    ;BOTTOM OF BUFFER
    movwf   FSR0H    
    movlw   low  (_dspbuff)
    movwf   FSR0L
LROW
    MOVLW   _NumberOfDisplays + 2;36 displays + 2 outside of display 
    movwf   _dcnt         ;display
    comf    WREG
    incf    WREG
    bcf     STATUS, C
Lcol
    rlcf    POSTINC0 ,f   ;PER display
    DECFSZ  _dcnt ,F
    BRA     Lcol
    BNC     LBNC
    bsf     PLUSW0,0       ;max displays would be 127 to use plusw
LBNC 
    DECFSZ  _bcnt ,F
    BRA     LROW
    banksel 0
    return
endasm

[richard]

with my suggestions it compiles for 18f47q43, whether it works is not tested . a quick browse of the q43 instruction set and access bank looks ok

[HenrikOlsson]

Bank 6 (or 7) doesn't work at all. I don't know what it's doing exactly. It does display the text but it does not scroll it.

Bank 5 (or 25) works - sort of.
I can scroll it left OR right continously without issues but when I change direction whatever is in the non visible part the buffer comes back on to the display shifted down by one row - at least I think that's what happening.

But it's fast, that's for sure.
* Mine was like 7ms or something like that
* tumblweeds was more than twice as fast at 3ms.
* Richards comes in at 0.2ms - amazing.

Mine and tumbleweeds simply scrolls the display, anything that's shifted outside of the buffer is lost while Richards rotates it so they're not exactly the same.

/Henrik.

[tumbleweed]

On most of the Q family the SFR registers are in banks 0-4, and the start of user ram is in bank 5.
That's where the access bank is (0x500-0x55F). The other part of the access bank is at 0x460-0x4FF, but that's for the fast SFR registers so you can't use that.
So, the "default" setting for 'banksel' should be 5 and not 0.

If you use the MOVFF instruction both the source and destination must be in the first 4K of ram space.
If either are outside that you need to use MOVFFL, which is a three-word instruction so it's more code (and slower) than MOVFF.

The K42/K83 force you to use MOVFFL to access SFR registers outside the access bank since on those the SFR regs are at the very top of ram.
That's one reason to skip the K42 and use the Q43 instead.

[richard]

I can scroll it left OR right continously without issues but when I change direction whatever is in the non visible part the buffer comes back on to the display shifted down by one row - at least I think that's what happening.

i expected to have had the buffer cleared out and reset before a direction change . however that sort of behavior is unanticipated

* Richards comes in at 0.2ms - amazing.

i get 0.1mS , maybe my oscilloscope is off



one of my clients sent me a test jig for q43 chips yesterday. i need to get into them soon i guess
no more excuses

@tumbleweed for confirming what i thought

[richard]

just for interest i tried my code on the st7920 buffer for rows 8 to 15 for the full 16 byte width of course



works as expected even when direction reversed midstream

[richard]

or a window to scroll
[i just can't help myself]

[HenrikOlsson]

i get 0.1mS , maybe my oscilloscope is off

Your scope is fine. All my quoted measurements are for my current configuration with 81 displays, so roughly double your measurement.

works as expected even when direction reversed midstream

It clearly does. Do you have a non visible are in the buffer? I can't see how it would matter but again, in my system it does weird things with what's outside the actual display.

The scrolling window was cool!

[richard]

Do you have a non visible are in the buffer?

no , i'm using a pointer into the the actual frame buffer of the display so i can't hide any data.
its vital that -
the width is in whole bytes ie for a 128x64 display thats 16 bytes
if i had a hidden byte each end then it would be 18
if you are short or long then the data will appear to move up or down at the wrap around
this may be clearer and can be applicable anywhere

note bank dependence has been eliminated

   
    width  con 128     ;display buffer width  and 
    height con 64      ;               height
    bcnt       VAR BYTE  
    dcnt       VAR BYTE   
    WindowWidth   CON 5     ;window is 5 bytes wide    scrolling window
    windowHeight  CON 8         ;window is 8 bits high             "     "
    @windowPad     =     _width/8 - _WindowWidth  ;number of bytes to get to start of next row
    @dspbuff =    _fbr+16*8+5       ;window start address row8 byte 5
;  fbr is the display frame buffer
rotate_r:  ' pic18
asm
    banksel _bcnt  ;ROW
    movlw   _windowHeight    
    movwf   _bcnt
    movlw   high (dspbuff)  ;BOTTOM OF BUFFER
    movwf   FSR0H    
    movlw   low  (dspbuff)
    movwf   FSR0L
    movlw   low((_WindowWidth )*_windowHeight-1) ;TOP OF BUFFER
    ADDWF   FSR0L 
    movlw   high((_WindowWidth )*_windowHeight-1)    
    ADDWFC  FSR0H
    MOVLW   _WindowWidth 
RROW
    banksel _dcnt 
    movwf   _dcnt        ;display
    bcf     STATUS, C
Rcol
    rrcf    POSTDEC0 ,f  ;PER display
    DECFSZ  _dcnt ,F
    BRA     Rcol
    BNC     RBNC
    bsf     PLUSW0,7     ;max would be 127 to use plusw
RBNC 
    banksel _bcnt 
    DECFSZ  _bcnt ,F
    BRA     RROW
    ;banksel 0
    return
endasm






rotate_l:  ' pic18
asm
    banksel _bcnt              ;ROW
    movlw   _windowHeight 
    movwf   _bcnt
    lfsr    0, dspbuff
LROW
    MOVLW   _WindowWidth 
    banksel _dcnt 
    movwf   _dcnt         ;
    comf    WREG
    incf    WREG
    bcf     STATUS, C
Lcol
    rlcf    POSTINC0 ,f   ;
    DECFSZ  _dcnt ,F
    BRA     Lcol
    BNC     LBNC
    bsf     PLUSW0,0       ;max  would be 127 to use plusw
LBNC 
    movlw   windowPad
    addwf   FSR0L ,f
    bnc     Lrnc
    incf    FSR0H ,f
Lrnc    
    banksel _bcnt 
    DECFSZ  _bcnt ,F
    BRA     LROW
    banksel 0
    return
endasm

ps window is rotate_l only . not done rr yet

[HenrikOlsson]

Aha, then that might be it as I have 81 displays so buffer is 83 bytes wide.
But again, it does not move down as it wraps around, only as it changes direction.