![Renesas mPD98431 Скачать руководство пользователя страница 60](http://html.mh-extra.com/html/renesas/mpd98431/mpd98431_user-manual_1440626060.webp)
CHAPTER 3 FUNCTIONAL DESCRIPTION
User’s Manual S14054EJ4V0UM
58
3.11.2 Receiving VLAN frames
If the value of the TPID field in a receive packet coincides with the value of the VLTP register, the VLAN bit of the
RSVREG register is set to 1. At this time, judgment related to the receive frame size is made based on MAX: 1522
bytes, MIN: 64 bytes. If filtering is performed by using the SIFT bit of the RFIC2 register (discarding short packet),
the reference packet is discarded when the data in the receive FIFO is less than 64 bytes even if the packet is
recognized as a VLAN frame.
3.11.3 Transmitting VLAN frames
If the APD bit of the MACC2 register is set to 1, the length of the transmit packet that is regarded as a VLAN
packet is judged based on MAX: 1522 bytes, MIN: 64 bytes. However, if the APD bit is 1 and the PADEN bit of the
MACC1 register is 1, pad and CRC are automatically appended to the transmit packets regarded as VLAN packets
with data of less than 68 bytes and the packets are transmitted as 68 bytes.
If a frame whose TPID field value does not coincide with the value of the VLTP register is transmitted, or if the
APD bit is 0, the processing is based on the normal frame size (MAX: 1518 bytes, MIN: 64 bytes).
If the VPD bit of the MACC2 register is 1, all the packets transmitted are regarded as VLAN frames and the above
operation proceeds, regardless of whether the TPID field value coincides with the VLTP register value. The setting of
the VPD bit takes precedence over the setting of the APD bit.
3.12 Statistics Counters
The
µ
PD98431 has a statistics counter set that is useful for implementing RMON and SNMP for each port. The
statistics counter is a 32-bit counter and supplies the upper layer with a total of 41 pieces of information on
transmission and reception.
The statistics counter counts and retains statistical parameters related to transmission/reception of packets (for
details of the parameters counted, refer to
CHAPTER 5 STATISTICS COUNTERS
). The counter is
µ
PDated each
time a packet has been transmitted or received. The status information is stored in the status FIFO in the
µ
PD98431
after an operation has been completed. Based on this information, the statistics counter is successively updated.
Each counter is cleared to 0 and continues counting if an overflow occurs. If an overflow occurs in a statistics
counter, or if an overrun occurs in the status FIFO, the corresponding bit of the CAR1 or CAR2 register is set to 1,
generating an interrupt. This interrupt can be masked for each counter by using the CAM1 and CAM2 registers.
The statistics counter is cleared by means of hardware reset.
3.13 Loopback
The MII transmit data stream is internally looped back as an MII receive data stream if the MACLB bit of the
MACC1 register is set to 1. TXCLKn is internally connected to RXCLKn. COLn and CRSn are ignored. To use
loopback, the FULLD bit of the MACC1 register must be set to 1 and the full-duplex operation mode must be set.
These settings can be made for each port independently.
3.14 Mirror Port Function
The mirror port function is used to monitor the status of a port specified by a register from a specific port. The
µ
PD98431 outputs the receive or transmit MII data stream of a port specified by the MIRR register as the transmit MII
data stream of a specific port. Refer to
Figure 3-15
.
Содержание mPD98431
Страница 4: ...User s Manual S14054EJ4V0UM 2 MEMO ...