; ---------------------------------------------------------------------------
; USB-1 -> CV routing patch for QuNexus firmware v2.2.1
;
; Goal: MIDI arriving on USB port 1 (Control Surface, cable 0) should also
; reach the CV engine. The stock firmware's CV_Out_Source only offers
; Expander / USB-3, so cable-0 events never enter the CV ring.
;
; Mechanism: retarget the single USB-MIDI dispatch call at 0xDF28 from the
; stock router (0xA57B) to a small stub (0x8126). The stub first runs the
; original router unchanged, then inspects the 4-byte USB-MIDI event buffer
; at 0x0F9B: if the event came in on cable 0 (top nibble == 0), it retags it
; as cable 2 (sets bit 0x20) and calls the router again so the event also
; lands in the USB-3 / CV ring. Events on any other cable pass through
; untouched (one router call, as stock).
;
; Abort-safety (matches patch_c2.py): the stub page (0x8000) is programmed
; BEFORE the retarget page (0xDE00), so a mid-failure never leaves a call to
; unprogrammed flash.
;
; This file assembles with sdas8051 (SDCC):  sdas8051 -l patch_usb1_to_cv.asm
; The resulting bytes must match exactly what patch_c2.py writes to the
; device over C2 (see verify_patch_asm.py).
; ---------------------------------------------------------------------------

    .area CODE (ABS)

; --- Stub routine (programmed into 0xFF padding at 0x8126, page 0x8000) ---
    .org 0x8126
usb1_cv_stub:
    lcall 0xa57b              ; 12 a5 7b  original cable-number router
    mov  dptr, #0x0f9b        ; 90 0f 9b  USB-MIDI 4-byte event buffer
    movx a, @dptr             ; e0        load event[0] (cable nibble in top 4 bits)
    anl  a, #0xf0             ; 54 f0     isolate cable number
    jnz  stub_done            ; 70 0b     not cable 0 -> nothing to mirror
    movx a, @dptr             ; e0        reload event[0]
    orl  a, #0x20             ; 44 20     retag cable 0 as cable 2
    movx @dptr, a             ; f0        store back
    mov  r6, #0x0f            ; 7e 0f     DPTR high = 0x0F (buffer page)
    mov  r7, #0x9b            ; 7f 9b     DPTR low  = 0x9B (buffer addr)
    lcall 0xa57b              ; 12 a5 7b  route again -> USB-3 / CV ring
stub_done:
    ret                       ; 22

; --- Retarget: the single dispatch call site (page 0xDE00) ---------------
; Stock at 0xDF28 is `lcall 0xa57b` (12 a5 7b). Patched to call the stub.
    .org 0xdf28
    lcall 0x8126              ; 12 81 26  -> usb1_cv_stub