8 .dseg

    13 ;; Matrix properties

     9 .set MATRIX_COLS = 8                        ; number of physical columns (XXX: fixed to 8)

    14 ; Matrix width in columns

    10 .set MATRIX_BUF_COLS = 16		            ; number of columns in frame buffer

    15 .set MATRIX_COLS = 8                        ; physical columns

    11 

    16 

    12 matrix_colbit:	    .byte 1					; scan column bit

    17 ; Framebuffer width in columns

    13 matrix_colbuf:	    .byte MATRIX_BUF_COLS	; row bits by column

    18 .set MATRIX_BUF_COLS = 16		            ; framebuffer columns

    14 matrix_colshift:    .byte 1                 ; left column offset

    19 

    20 ;; SPI addresses

    21 ; row drivers (8 bits)

    22 .set MATRIX_SPI_ROW = 0                     ; row mask source

    23 

    24 ; column sinks (8 bits)

    25 .set MATRIX_SPI_COL = 1                     ; column scan sink

    26 

    27 ;; Matrix state

    28 ; Matrix framebuffer

    29 ; this holds the columns data as a 1 byte bitmask of row data per column (8 bits -> 8 rows)

    30 matrix_colbuf:	    .byte MATRIX_BUF_COLS   ; framebuffer (row data by column)

    31 

    32 ; Column scan bit

    33 ; in the matrix refresh loop, we push out each column's row data in turn

    34 ; this bit tracks the currently refreshing column

    35 matrix_colbit:	    .byte 1                 ; column scan bit

    36 

    37 ; Matrix viewport offset

    38 ; the visible matrix data is taken directly from the framebuffer, but it can be taken at an arbitrary offset

    39 ; this determines the starting offset for the visible viewport's left edge from the start of the framebuffer in columns

    40 matrix_colshift:    .byte 1                 ; viewport left column offset

    18 ;; Normalize the outputs, enable the matrix, an set up buffers

    44 ;; Normalize the outputs, enable the matrix, and set up buffers

    62 ;; Scan the next column

    88 ;; Scan the matrix's next column from the viewport

    76 		; output

   102 		; output single column-enable bit

   115 		; output

   141 		; output full row-enable bitmask

   178 ;; Shift the matrix output one column to the right, looping around

   205 ;; Reset the viewport to the start (left edge) of the framebuffer

   179 Matrix_ShiftRight:

   206 Matrix_ShiftZero:

   207     ; Constant offset

   208         ldi         r16, 0

   209 

   210     ; Set

   211         rjmp        Matrix_ShiftSet

   212 

   213 ;; Shift the viewport one column to the left in the framebuffer, looping around to the end of the framebuffer

   214 ; This moves the visible output one column to the right

   215 Matrix_ShiftLeft:

   187         ; test for underflow -> MSB/N set

   223         ; test for underflow (MSB/N set) -> don't skip reset

   193     ;; Continue

   229     ; Set

   194 

   230         rjmp        Matrix_ShiftSet

   195 ;; Set the matrix output left shift

   231 

   232 ;; Shift the viewport one column to the right in the framebuffer, looping around to the start of the FB

   233 ; This moves the visible output one column to the left

   234 Matrix_ShiftRight:

   235     ; Increment-loop current value

   236         ; current value

   237         lds         r16, matrix_colshift

   238 

   239         ; shift window right

   240         inc         r16

   241 

   242         ; test for overflow -> don't skip reset

   243         cpi         r16, MATRIX_BUF_COLS - MATRIX_COLS

   244         brlt        Matrix_ShiftSet

   245 

   246         ; reset window to left edge

   247         ldi         r16, 0

   248 

   249     ; Set

   250         rjmp        Matrix_ShiftSet

   251 

   252 ;; Set the matrix viewport offset