Interrupts; Operation; Setup - Rabbit 6000 User Manual

25.2.4 Interrupts

The network interrupt can be generated by an Ethernet frame being transmitted correctly, trans-
mitted with an error, or if a transmit pause occurs (control frame is transmitted but not the data).
The events that generate an interrupt can be selected in NBCSR.
The receive frame status is attached to the end of the data frame itself, so the DMA interrupt can
be used to handle received frame. See Section 25.3 for more details.
The network port interrupt vector is located in the IIR at offset 0x1E0. It can be set at Priority 1, 2,
or 3 by writing to NBCSR.

25.3 Operation

High-level support for TCP/IP and other protocols is beyond the scope of this manual, but this
section will describe the low-level setup and operation of the 10/100Base-T Ethernet peripheral.
Dynamic C has the necessary drivers.
The contents of the six status bytes are shown below. Note that any status block marked with
RxOV (receive overflow) is invalid, as the FIFO could not hold the entire frame. Only the marked
frame is invalid, so any previous frames read from the FIFO are fine. Once an overflow is
detected, no subsequent frames can be buffered to the FIFO until a FIFO purge command is writ-
ten to the NBCR.
Status Byte Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
First LSB of Rx Checksum
Second MSB of Rx Checksum
Third Receive Status Vector [7:0] (LSB of receive frame length)
Fourth Receive Status Vector [15:8] (MSB of receive frame length)
Fifth Receive Status Vector [23:16]
Last RxOV Receive Status Vector [30:24]

25.3.1 Setup

The following steps explain how to set up Network Port B.
1. In MSCR, select shared clock if the main clock is 25 MHz, and reset the PHY if desired.
2. Enable Network Port B by writing to ENPR.
3. Write the interrupt vector for the interrupt service routine to the external interrupt table.
4. Select the desired interrupts and interrupt priority by writing to NBCSR.
5. Select the MII interface settings by writing to NBMCFR, NBMRAR, and NBMPAR.
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