k2 816 core2x w6100 read fifo contains an extra byte at the start in 24-bit mode

[ghackwrench]

See below for the reproduce.

Hardware version

• Machine type: Wildbits/K2
• PCB revision: purple board (?)
• CPU: 65816
• Speed: 2x

[ghackwrench]

complete_rx
          ; A receive transfed has completed.
          ; The data is in the RX fifo.
          ; A = packet buffer, Y=tail

          ; Buffer in X
            tax

          ; Copy the data out of the fifo.
            phx
            phy
            lda @l  kernel.net.packet.length,x
            tay

          ; The Foenix138_B3B_July27th_2025 load
          ; contains a bug that leaves an extra
          ; byte at the start of the w6100 fifo.
            bit     core2x
            bmi +
            lda     PORT
          +

            sep #$20
          - lda     PORT
            sta @l  kernel.net.packet.ethernet,x
            inx
            dey
            bne -
            rep #$20
            ply
            plx

          ; Resume driver.
            txa
            clc     ; rx complete.
            jmp     return