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-This file documents the driver changes needed to support use as part
-of a PXE stack.
-
-PROPER WAY
-==========
-
-1. The probe() routine.
-
-There are three additional fields that need to be filled in the nic
-structure: ioaddr, irqno and irq.
-
- ioaddr is the base I/O address and seems to be for information only;
- no use will be made of this value other than displaying it on the
- screen.
-
- irqno must be the IRQ number for the NIC. For PCI NICs this can
- simply be copied from pci->irq.
-
- irq is a function pointer, like poll and transmit. It must point to
- the driver's irq() function.
-
-2. The poll() routine.
-
-This must take an additional parameter: "int retrieve". Calling
-poll() with retrieve!=0 should function exactly as before. Calling
-poll() with retrieve==0 indicates that poll() should check for the
-presence of a packet to read, but must *not* read the packet. The
-packet will be read by a subsequent call to poll() with retrieve!=0.
-
-The easiest way to implement this is to insert the line
- if ( ! retrieve ) return 1;
-between the "is there a packet ready" and the "fetch packet" parts of
-the existing poll() routine.
-
-Care must be taken that a call to poll() with retrieve==0 does not
-clear the NIC's "packet ready" status indicator, otherwise the
-subsequent call to poll() with retrieve!=0 will fail because it will
-think that there is no packet to read.
-
-poll() should also acknowledge and clear the NIC's "packet received"
-interrupt. It does not need to worry about enabling/disabling
-interrupts; this is taken care of by calls to the driver's irq()
-routine.
-
-Etherboot will forcibly regenerate an interrupt if a packet remains
-pending after all interrupts have been acknowledged. You can
-therefore get away with having poll() just acknolwedge and clear all
-NIC interrupts, without particularly worrying about exactly when this
-should be done.
-
-3. The irq() routine.
-
-This is a new routine, with prototype
- void DRIVER_irq ( struct nic *nic, irq_action_t action );
-"action" takes one of three possible values: ENABLE, DISABLE or FORCE.
-ENABLE and DISABLE mean to enable/disable the NIC's "packet received"
-interrupt. FORCE means that the NIC should be forced to generate a
-fake "packet received" interrupt.
-
-If you are unable to implement FORCE, your NIC will not work when
-being driven via the UNDI interface under heavy network traffic
-conditions. Since Etherboot's UNDI driver (make bin/undi.zpxe) is the
-only program known to use this interface, it probably doesn't really
-matter.
-
-
-QUICK AND DIRTY WAY
-===================
-
-It is possible to use the system timer interrupt (IRQ 0) rather than a
-genuine NIC interrupt. Since there is a constant stream of timer
-interrupts, the net upshot is a whole load of spurious "NIC"
-interrupts that have no effect other than to cause unnecessary PXE API
-calls. It's inefficient but it works.
-
-To achieve this, simply set nic->irqno=0 in probe() and point nic->irq
-to a dummy routine that does nothing. Add the line
- if ( ! retrieve ) return 1;
-at the beginning of poll(), to prevent the packet being read (and
-discarded) when poll() is called with retrieve==0;
-
-
-UNCONVERTED DRIVERS
-===================
-
-Drivers that have not yet been converted should continue to function
-when not used as part of a PXE stack, although there will be a
-harmless compile-time warning about assignment from an incompatible
-pointer type in the probe() function, since the prototype for the
-poll() function is missing the "int retrieve" parameter.