INT 7C - SK-UPPS Data Link Interface API - REGISTER PROTOCOL
        AX = 0007h
        ES:BX -> Protocol Control Block (see below)
Return: AX = completion code (see AX=0001h)
Program: SK-UPPS is the Schneider & Koch Universal Portable Protocol Stack,
          which provides an API on top of its Data Link Interface, allowing the
          use of any of several network transport layers
SeeAlso: AX=0008h,AX=000Bh

Format of Protocol Control Block (PCB):
Offset  Size    Description
 00h    WORD    protocol type (high-low)
 02h    WORD    protocol mode (see below)
 04h    DWORD   -> Receive Upcall routine
 08h    DWORD   -> Transmit Upcall routine
 0Ch    DWORD   -> Event Upcall routine
 10h    DWORD   -> ASCIZ protocol name (zero if none)
 14h    WORD    protocol ID will be returned here (always non-zero)

Bitfields for protocol mode:
 bit 0  promiscuous mode; protocol receives all frames regardless of their
          destination (PROTOCOL TYPE must be FFFFh)
 bit 1  if set, protocol's Event Upcall will be called on entry and exit of the
          DLI's Interrupt Service Routine (see event codes below)
 bit 2  DLI 2.2+ hook mode; protocol receives all directed frames destined for
          this station (PROTOCOL TYPE must be FFFFh)
 bit 3  DLI 2.3+ receive error frames (only valid in promiscuous mode (bit 0))
 bit 4-5 DLI 2.5+ frame type:
        00 Ethernet II; specify type code in PROTOCOL TYPE field (high-low)
        01 IEEE 802.2; specify Service Access Point (SAP) in MSB
            (offset 0) of PROCOTOL TYPE field; LSB must be zero
        10 IEEE 802.2 with SNAP header; specify type code in PROTOCOL TYPE
            field (high-low)
        11 reserved (currently unused)
 bit 6  DLI 2.5+ if set, protocol's Event Upcall will be called with event code
          EV_BUFFER_WANTED, when DLI runs out of Mbufs
 bit 7  DLI 2.7+ chain mode; if set, client allows the specified frame type to
          be shared with other clients
 bit 8  DLI 2.8+ receive non-LLC frames rather than LLC frames
 bit 9  DLI 2.8+ receive all multicast frames (see also AX=0009h)
 bit 10-15 reserved (currently unused; must be zero)
Notes:  If PROTOCOL TYPE is FFFFh and neither the "promiscuous" nor the "hook"
          mode bit is set, the protocol receives all frames that did not match
          any registered frame type (demultiplexor mode).
        Protocols using "promiscuous", "hook" or "chain" mode should always
          return from the Receive Upcall with the received Mbuf in ES:BX and the
          Carry Flag set. The DLI will then pass the Mbuf to the FEED BACK
          BUFFER function (see AX=000Fh).
        Some DLIs do not support all or even any of the "promiscuous",
          "receive non-LLC" and "receive all multicasts" mode bits.

Receive Upcall called with:
 ES:BX -> Mbuf
 AX = receive status (see below; also stored in Mbuf's RECEIVE STATUS field)
 interrupts disabled

Bitfields for receive status (reserved bits currently unused and always zero):
 bit 0-2 reserved
 bit 3  frame check sequence (FCS) error
 bit 4  overflow (frame too long)
 bit 5  framing error
 bit 6  reserved
 bit 7  non-LLC frame (see bit 8 of PCB's protocol mode field)
 bit 8-15 reserved
Notes:  The protocol's Receive Upcall routine will be called whenever a frame
          matching the specified frame type is received. A received frame is
          passed to the protocol in the Mbuf's DATA area at OFFSET and its size
          is LENGTH bytes.
        The receive status passed to the Receive Upcall in register AL is
          always zero, except for protocols using "non-LLC" mode (bit 8 of PCB's
          protocol mode field) or "promiscuous" mode together with "receive
          error frames" (bits 0 & 3).
        Upcalls are FAR routines and must return with a RET FAR. If the Carry
          Flag is set on return from a Receive or Transmit Upcall, then ES:BX
          must point to an Mbuf, which the DLI will then pass to the RELEASE
          BUFFER function (see AX=0005h). See also notes for PROTOCOL MODE.

Event Upcall called with:
 AX = event code (see below)
Note:   All Event Upcalls may be ignored by the protocol.

Event codes found in register AX on Event Upcall:
 00h EV_BUFFER_AVAILABLE  client may now call REQUEST BUFFER (AX=0004h)
 01h EV_ISR_START       start of Interrupt Service Routine
 02h EV_ISR_END         end of ISR (see bit 1 in PCB's protocol mode field)
 03h EV_BUFFER_WANTED   DLI temporarily out of Mbufs
 04h EV_NETWORK_STATUS  DLI 2.8+ network status (DX=status; see below)
 05h EV_IO_CONTROL      DLI 2.8+ I/O control (DX=subfunction; see AX=0016h)

Bitfields for EV_NETWORK_STATUS in register DX:
        Token-Ring              FDDI
 bit 15 SIGNAL_LOSS             SIGNAL_LOSS
 bit 14 HARD_ERROR              HARD_ERROR
 bit 13 SOFT_ERROR              SOFT_ERROR
 bit 12 TRANSMIT_BEACON         TRANSMIT_BEACON
 bit 11 LOBE_WIRE_FAULT         PATH_TEST_FAILED
 bit 10 AUTO_REMOVAL            SELF_TEST_REQUIRED
 bit 9  reserved                reserved
 bit 8  REMOVE_RECEIVED         REMOTE_DISCONNECT
 bit 7  COUNTER_OVERFLOW        reserved
 bit 6  SINGLE_STATION          DUPLICATE_ADDRESS
 bit 5  RING_RECOVERY           NO_RING_OP_STATUS
 bit 4  reserved                VERSION_MISMATCH
 bit 3  reserved                STUCK_BYPASS
 bit 2  reserved                FDDI_EVENT
 bit 1  reserved                RING_OP_CHANGE
 bit 0  reserved                reserved
Note:   EV_NETWORK_STATUS is not supported on Ethernet

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