I'm starting to analyze the WDC Self-Test Firmware Routine. Starting trigger was 0x8001 (WDC Unit Register) + Status 0x02 (I/O reference - see Handbook 03-3237-04 Page 4-8)
2356 21078001 ld r7,#%8001
235a cea5 ldb rl6,#%a5
235c 3e7e outb @r7,rl6
235e 3c76 inb rh6,@r7
2360 8ae6 cpb rh6,rl6
2362 e605 jr z,%236e
2364 4c0147480303 cpb %4748,#%03
236a 9e0e ret nz
236c e821 jr %23b0
236e 91f0 pushl @r15,rr0