
98
STP2002QFP
Sun Microelectronics
Fast Ethernet, Parallel Port, SCSI (FEPS) - STP2002QFP
The default value of this register is set to 0x3FE
7.5.7 ETX Transmit Descriptor Pointer (RW)This 29-bit register points to the next descriptor in the ring. The 21 most sig-
nificant bits are used as the base address for the descriptor ring, while the 8
least significant bits are used as a displacement for the current descriptor.
Note: The transmit descriptor pointer must be initialized to a 2K byte-
aligned value after power-on or software reset.
7.5.8 ETX Transmit Descriptor Ring SizeThis four-bit register determines the number of descriptor entries in the ring.
The number of entries can vary from 16 through 256 in increments of 16.
Table 101: ETX Configuration Register Definition
Field Bits Description Type
Tx_DMA_Enable 0 When set to 1, the DMA operation of the channel
is enabled. The load control state machine will
respond to the next TX_Pending command. When
cleared to 0, the DMA operation of the channel
will cease as soon as the transfer of the current data
buffer has been completed
R/W
Tx_FIFO_Threshol
d
9:1 This field determines the number of packet data
words that will be loaded into the TxFIFO before
the frame transmission by the TX_MAC is
enabled.
The maximum allowable threshold is 1BF. If the
desire is to buffer an entire standard Ethernet
frame before transmission is enabled, this field has
to be programmed to a value greater than 1BF.
R/W
Paced_Mode 10 When set to 1, the Tx_All interrupt (bit 25 in the
global status register) will become set only after
the TxFIFO becomes empty. If cleared to 0, the
Tx_All interrupt will function as described in
“Global Interrupt Mask Register (RW)” section on
page 94.
R/W
Table 102: ETX Transmit Descriptor Pointer Register Address
Register Physical Address Access Size
ETX transmit descriptor pointer register 0x8C0_2008 4 bytes