Digi Rabbit 5000, User Manual

Page: 263 / 414

Chapter 22 10/100Base-T Ethernet 263
22.2.4 Interrupts
The network interrupt can be generated by an Ethernet frame being transmitted correctly,
transmitted 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 inter-
rupt can be used to handle received frame. See Section 22.3 for more details.
The network port interrupt vector is shared with Network Port C, the Wi-Fi network port.
It is located in the IIR at offset 0x1E0. It can be set as Priority 1, 2, or 3 by writing to ENPR.
22.3 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.
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 written 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]