INT 21 - Turbo Debug HARDWARE BREAKPOINTS - READ STATUS BLOCK
        AH = 3Fh
        BX = handle for character device "TDHDEBUG"
        CX = number of bytes to read
        DS:DX -> buffer for status block (see below)
Return: CF clear if successful
            AX = number of bytes actually read
        CF set on error
            AX = error code (05h,06h) (see AH=59h)

Format of status block:
Offset  Size    Description
 00h    BYTE    status of command
                00h successful
                01h invalid handle
                02h no more breakpoints available
                03h hardware does not support specified breakpoint type
                04h previous command prevents execution
                05h debugger hardware not found
                06h hardware failure
                07h invalid command
                08h driver not initialized yet
                FEh recursive entry (hardware breakpoint inside hw bp handler)
---status for command 01h---
 01h    WORD    device driver interface version number (currently 1)
 03h    WORD    device driver software version
 05h    BYTE    maximum simultaneous hardware breakpoints
 06h    BYTE    configuration bits
                bit 0: CPU and DMA accesses are distinct
                    1: can detect DMA transfers
                    2: supports data mask
                    3: hardware pass counter on breakpoints
                    4: can match on data as well as addresses
 07h    BYTE    supported breakpoint types
                bit 0: memory read
                    1: memory write
                    2: memory read/write
                    3: I/O read
                    4: I/O write
                    5: I/O read/write
                    6: instruction fetch
 08h    WORD    supported addressing match modes
                bit 0: any address
                    1: equal to test value
                    2: not equal
                    3: above test value
                    4: below test value
                    5: below or equal
                    6: above or equal
                    7: within range
                    8: outside range
 0Ah    WORD    supported data matches
                bit 0: any data
                    1: equal to test value
                    2: not equal
                    3: above test value
                    4: below test value
                    5: below or equal
                    6: above or equal
                    7: within range
                    8: outside range
 0Ch    BYTE    maximum data match length (01h, 02h, or 04h)
 0Dh    WORD    size of onboard memory (in K)
 0Fh    WORD    maximum number of trace-back events
 11h    WORD    hardware breakpoint enable byte address segment (0000h if not
                supported)
---status for command 04h---
 01h    BYTE    handle to use when referring to the just-set breakpoint