46
STP2002QFP
Sun Microelectronics
Fast Ethernet, Parallel Port, SCSI (FEPS) - STP2002QFP

Figure 12. TxFIFO Organization

5.4.8 Other User Accessible Resources

Besides the host and local memory data structures, the hardware provides a

programmed I/O path to a variety of hardware resources for initialization, er-

ror recovery, diagnostics, and network management. From the software per-

spective, all the programmable resources should be treated as 32-bit entities.

If not all 32 bits are used in a register, the unused bits are grouped as the most

significant bits of the word. Register fields that are not used are ignored dur-

ing a PIO write, and return 0s during a PIO read. The description of these re-

sources is grouped by functionality and not necessarily by their physical

location. The default value for all the registers/counters is 0x00000000, un-

Frame #1 Data Frame #1 Data
Frame #1 Control 32-Bit
Mode
Wrap-
Around
FIFO
64-Bit
Mode
031
32
Tag_1
63
Tag_0
Addr_0
junk
Shadow
Read_Ptr
0
.
.
.
.
0
0
1
0
.
.
.
.
0
0
1
Read_Ptr Frame #2 Data Frame #2 Data
Frame #2 Control
0
.
.
.
.
0
0
1
0
.
.
.
.
0
1junk
Frame #3 Data
.
.
.
.
Frame #3 Data
.
.
.
.
0
.
.
.
.
.
.
0
.
.
.
.
.
Shadow
Write_Ptr
Frame #n Data Frame #n Data
0
.
.
.
0
0
1
1Frame #n Control Frame #n Control
junk
junk
Write_Ptr
x
x
x
x
x
x
x
x
Addr 255
Tag_0/Tag_1
1Reserved Byte
Boundary
20
Frame Control
Word