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)
SeeAlso: AH=40h"Turbo Debug"

Values for 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)

Format of status block:
Offset  Size    Description
 00h    BYTE    status of command (see above)
---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 (see below)
 07h    BYTE    supported breakpoint types (see below)
 08h    WORD    supported addressing match modes (see below)
 0Ah    WORD    supported data matches (see below)
 0Ch    BYTE    maximum data match length (01h, 02h, or 04h)
 0Dh    WORD    size of onboard memory (in KB)
 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

Bitfields for configuration bits:
 bit 0  CPU and DMA accesses are distinct
 bit 1  can detect DMA transfers
 bit 2  supports data mask
 bit 3  hardware pass counter on breakpoints
 bit 4  can match on data as well as addresses

Bitfields for supported breakpoint types:
 bit 0  memory read
 bit 1  memory write
 bit 2  memory read/write
 bit 3  I/O read
 bit 4  I/O write
 bit 5  I/O read/write
 bit 6  instruction fetch

Bitfields for supported addressing match modes:
 bit 0  any address
 bit 1  equal to test value
 bit 2  not equal
 bit 3  above test value
 bit 4  below test value
 bit 5  below or equal
 bit 6  above or equal
 bit 7  within range
 bit 8  outside range

Bitfields for supported data matches:
 bit 0  any data
 bit 1  equal to test value
 bit 2  not equal
 bit 3  above test value
 bit 4  below test value
 bit 5  below or equal
 bit 6  above or equal
 bit 7  within range
 bit 8  outside range

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