Peripherals—IP2022 User’s Manual 292 www.ubicom.com Software must perform the following functions: • Polarity detection and reversal. • Carrier sense. • Jabber detection. • Link integrity test and link pulse generation. • Random back off in case of collision. • When a collision is detected, sending a 32-bit jam sequence.
Collisions can be detected by either receiving an RXXCRS in-
terrupt or  by  setting  the bit  count to  7  and then  received  a
RXBF interrupt while transmitting. • Formation  of  Ethernet  packet  by  putting  the  preamble,  sfd,
destination address, source address, length/type, MAC client
data into the transmit buffer. Frame check computation also
must be done in software. • MAC layer functions. GPSI Interface GPSI  is a general-purpose,  point-to-point,  full-duplex  serial  bus
protocol. Only two devices are allowed to exist on a bus. The GPSI
master device is responsible for maintaining bus timing by driving
two  continuously  running  clocks,  TxClk  and  RxClk.  The  device
that does not drive the clocks is the slave device. The TxEn and
TxD signals are synchronized to the TxClk clock. The RxD and
RxEn signals are synchronized to the RxClk clock. The mapping
of GPSI signals to IP2022 signals is shown in Table 4-9.