BSP Developer's Guide

VxWorks 5.5
BSP Developer’s Guide
G.1.1 Structure of a 4.3 BSD Network Driver
The network drivers currently shipped with VxWorks are based on those available
in BSD UNIX version 4.3. These drivers define only one global (user-callable)
routine, the driver’s attach( ) routine. Typically, the name of this routine contains
the word, attach, prefixed with two letters from the device name. For example, the
AMD Lance driver’s attach routine is called lnattach( ). The xxattach( ) routine
hooks in five function pointers that are mapped into an ifnet structure. These
functions, listed in Table G-1, are all called from various places in the IP protocol
stack, which has intimate knowledge of the driver.
Table G-1
Network Interface Procedure Handles
Function Function Pointer Driver-Specific Routine
initialization if_init xxInit( )
output if_output xxOutput( )
control if_ioctl xxIoctl( )
reset if_reset xxReset( )
watchdog if_watchdog (optional) xxWatchdog( )
Packet reception begins when the driver’s interrupt routine is invoked. The
interrupt routine does the least work necessary to get the packet off the local
hardware, schedules an input handler to run by calling netJobAdd( ), and then
returns. The tNetTask calls the function that was added to its work queue. In the
case of packet reception, this the driver’s xxReceive( ) function.
The xxReceive( ) function eventually sends the packet up to a protocol by calling
do_protocol_with_type( ). This routine is a switch statement that figures out
which protocol to hand the packet off to. This calling sequence is shown in
Figure G-1.
Figure G-2 shows the call graph for packet transmission. After a protocol has
picked an interface on which to send a packet, it calls the xxOutput( ) routine for
that interface. The output routine calls the generic ether_output( ) function,
passing it a pointer to addressing information (usually an arpcom structure) as
well as the data to be sent. After the data is properly packed, it is placed on the
output queue (using the IF_ENQUEUE macro), and the driver’s start routine is
called. The xxTxStartup( ) routine dequeues as many packets as it can and
transmits them on the physical medium.
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