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參數(shù)資料
| 型號： | NS32490D |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | NIC Network Interface Controller(NIC網(wǎng)絡(luò)接口控制器) |
| 中文描述： | NIC網(wǎng)絡(luò)接口控制器（NIC網(wǎng)絡(luò)接口控制器） |
| 文件頁數(shù)： | 11/56頁 |
| 文件大?。?/td> | 689K |
| 代理商： | NS32490D |
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7.0 Packet Reception
(Continued)
3. After a packet is DMAed from the Receive Buffer Ring,
the Next Page Pointer (second byte in NIC buffer header)
is used to update BNDRY and nextDpkt.
nextDpkt
e
Next Page Pointer
BNDRY
e
Next Page Pointer
b
1
If BNDRY
k
PSTART then BNDRY
e
PSTOP
b
1
Note the size of the Receive Buffer Ring is reduced by one
256-byte buffer; this will not, however, impede the operation
of the NIC.
In StarLAN applications using bus clock frequencies greater
than 4 MHz, the NIC does not update the buffer header
information properly because of the disparity between the
network and bus clock speeds. The lower byte count is cop-
ied twice into the third and fourth locations of the buffer
header and the upper byte count is not written. The upper
byte count, however, can be calculated from the current
next page pointer (second byte in the buffer header) and the
previous next page pointer (stored in memory by the CPU).
The following routine calculates the upper byte count and
allows StarLAN applications to be insensitive to bus clock
speeds. NextDpkt is defined similarly as above.
1st Received Packet Removed By Remote DMA
TL/F/8582–57
upper byte count
e
next page pointer
b
nextDpkt
b
1
if (upper byte count)
k
0 then
upper byte count
e
(PSTOP
b
nextDpkt)
a
(next page pointer
b
PSTART)
b
1
if (lower byte count)
l
0 fch then
upper byte count
e
upper byte count
a
1
STORAGE FORMAT FOR RECEIVED PACKETS
The following diagrams describe the format for how re-
ceived packets are placed into memory by the local DMA
channel. These modes are selected in the Data Configura-
tion Register.
Storage Format
AD15
AD8
AD7
AD0
Next Packet
Pointer
Receive
Status
Receive
Byte Count 1
Receive
Byte Count 0
Byte 2
Byte 1
BOS
e
0, WTS
e
1 in Data Configuration Register.
This format used with Series 32000 808X type processors.
AD15
AD8
AD7
AD0
Next Packet
Pointer
Receive
Status
Receive
Byte Count 0
Receive
Byte Count 1
Byte 1
Byte 2
BOS
e
1, WTS
e
1 in Data Configuration Register.
This format used with 68000 type processors.
Note:
The Receive Byte Count ordering remains the same for BOS
e
0 or 1.
AD7
AD0
Receive Status
Next Packet
Pointer
Receive Byte
Count 0
Receive Byte
Count 1
Byte 0
Byte 1
BOS
e
0, WTS
e
0 in Data Configuration Register.
This format used with general 8-bit CPUs.
8.0 Packet Transmission
The Local DMA is also used during transmission of a pack-
et. Three registers control the DMA transfer during trans-
mission, a Transmit Page Start Address Register (TPSR)
and the Transmit Byte Count Registers (TBCR0,1). When
the NIC receives a command to transmit the packet pointed
to by these registers, buffer memory data will be moved into
the FIFO as required during transmission. The NIC will gen-
erate and append the preamble, synch and CRC fields.
TRANSMIT PACKET ASSEMBLY
The NIC requires a contiguous assembled packet with the
format shown. The transmit byte count includes the Destina-
tion Address, Source Address, Length Field and Data. It
does not include preamble and CRC. When transmitting
data smaller than 46 bytes, the packet must be padded to a
minimum size of 64 bytes. The programmer is responsible
for adding and stripping pad bytes.
General Transmit Packet Format
TL/F/8582–58
11
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