7-4
BajaPPC-750: Ethernet Interface
7.3 Default Ethernet Boot Device
The Intel 21143 supports a variety of Ethernet modes. Since the hardware alone
cannot determine the Ethernet configuration, the BajaPPC-750 provides a means
for software to detect the mode via the jumper installations at JP1. These jumpers
indicate the default Ethernet boot device as follows:
In order to determine the Ethernet mode, the software can manipulate the CSR9
command/status register on the Intel 21143. This register is located at hex offset
48
16
in PCI space. Please see the
21143 Hardware Reference Manual
for complete
details regarding the CSR9 register.)
The BR bit selects the boot ROM port on the 21143 device. The jumpers at JP1 are
tied to the first three boot ROM address/data lines on the 21143. When BR is set
and the software sets the ROM read (RD) bit, the jumper status appears in bits 2:0
of the DATA field. If a jumper is present, it pulls the corresponding data line low.
Bit 2 corresponds to the status of JP1 pins 1–2; bit 1 corresponds to pins 3–4, and
bit 0 corresponds to pins 5–6. The remaining DATA bits are pulled high
(reserved).
7.4 21143 Errata
The Intel 21143 chip “Extraneous Word During Transmit” problem can cause
trouble for low-level software, such as test routines. The 21143 can intermittently
insert two extra bytes into the transmitted packet, causing the receiving station
to calculate a CRC error. For additional information regarding this and other
21143 errata, please refer to the
Errata Revision 4.0 (May 22, 1998)
document,
which is available from Intel technical support. (See Section 1.4.3.)
Table 7-3. Default Ethernet Boot Device Selection (JP1)
Jumpers
1
installed at JP1 on:
1. Spare jumpers are located at JP2 (board revs. 1 and 21 only).
Ethernet mode
selection:
CSR9 DATA
bits:
pins 1–2
(Bit 2)
pins 3–4
(Bit 1)
pins 5–6
(Bit 0)
yes
yes yes AUI
11111000
no
yes
yes
MII/SYM with rate detection (
default
)
11111100
–
–
–
All other combinations are reserved
–
31 : 20
19
18
17
16
15
14
13
12
11
10
9 : 8
7 : 0
reserved
MDI
MII
MDO
MDC
RD
WR
BR
SR
REG
DATA
Register Map 7-1. Intel 21143 General Purpose Command/Status, CSR9
Содержание BajaPPC-750
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