Introduction to Data Communications
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Packet drivers use software interrupts to identify the network cards to the data link layer. Packet drivers are free software drivers that were developed to address the problems of running multiple protocols over one network card. NDIS and ODI are proprietary schemes that have been developed by 3COM/Microsoft and Novell/Apple respectively to address this problem.

The Crynwr Software collection of packet drivers are available throughout the Internet and they are free to use unlike shareware and commercial products.

Advantages:

• Run multiple applications across the same board: TCP/IP, NetBIOS, Netware
• One board fits all, no buying different boards for different applications.
• No more reconfiguring and rebooting to change applications.
• Connect to a Novell File Server (or servers) and still run TCP/IP or PC-NFS or with the Novell systems remaining active and available for file serving and printing.

The Packet Driver acts as a fast smart secretary, bothering clients only when packets arrive specifically for them.

Software Interrupts

Software interrupts are interrupts generated by software unlike hardware interrupts that are physical lines that run to each device. Software interrupts that are available are 0x60 to 0x66. Table xx-1 lists the software interrupts and their assignments.

The packet drivers are assigned software interrupts to the network interface card during the bootup process usually in the autoexec.bat file. For a 3c503 card the autoexec.bat file would have this line:

where:

• 3c509 calls up the packet driver 3c509.com
• 0x60 is the software interrupt assigned to the NIC
• 5 is the hardware interrupt of the NIC
• 0x300 is the I/O address of the NIC

Any network traffic received or transmitted from the NIC would be addressed by the software interrupt 0x60. Complete documentation is available from the Crynwr collection under the files. Important files to read are install.doc and packet.doc.

Software Interrupts Assignments

	60 -- -- reserved for user interrupt
	61 -- -- reserved for user interrupt
	62 -- -- reserved for user interrupt
	63 -- -- reserved for user interrupt
	64 -- -- reserved for user interrupt
	65 -- -- reserved for user interrupt
	66 -- -- reserved for user interrupt
	67 -- -- LIM EMS
	68 01 -- APPC/PC
	69 -- -- unused
	6A -- -- unused
	6B -- -- unused
	6C -- -- DOS 3.2 Realtime Clock update
	6D -- -- VGA - internal
	6E -- -- unused
	6F -- -- Novell NetWare
 	70 -- -- IRQ8 - AT/XT286/PS50+ - REAL-TIME CLOCK
	71 -- -- IRQ9 - AT/XT286/PS50+ - LAN ADAPTER 1
	72 -- -- IRQ10 - AT/XT286/PS50+ - RESERVED
	73 -- -- IRQ11 - AT/XT286/PS50+ - RESERVED
	74 -- -- IRQ12 - PS50+ - MOUSE INTERRUPT
	75 -- -- IRQ13 - AT/XT286/PS50+ - 80287 ERROR
	76 -- -- IRQ14 - AT/XT286/PS50+ - FIXED DISK
	77 -- -- IRQ15 - AT/XT286/PS50+ - RESERVED
	78 -- -- not used
	79 -- -- not used
	7A -- -- Novell NetWare - LOW-LEVEL API
	7A -- -- AutoCAD Device Interface
	7B -- -- not used
	7C -- -- not used
	7D -- -- not used
	7E -- -- not used
	7F -- -- HDILOAD.EXE - 8514/A VIDEO CONTROLLER INTERFACE
	80 -- -- reserved for BASIC

Introduction to Data Communications
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