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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Order Number: 306262-004US
871
Synchronous Serial Port—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
the ROR bit is asserted, and the newly received data is discarded. This process is
repeated for each new piece of data received until at least one empty FIFO entry exists.
When the ROR bit is set, an interrupt request is made. Writing 1 to this bit resets ROR
status and its interrupt request.
After this ROR interrupt occurs, it is recommended that the user read the receive FIFO
to empty it, then clear the ROR bit.
20.5.3.7
Transmit FIFO Level (TFL)
This 4-bit value shows how many valid entries are currently in the Transmit FIFO.See
register table below for details.
20.5.3.8
Receive FIFO Level (RFL)
This 4-bit value shows how many valid entries are currently in the Receive FIFO. See
register table below for details.
The following bit table shows the bit locations corresponding to the status and flag bits
within the SSP status register. All bits are read-only except ROR, which is read/write.
Writes to TNF, RNE, BSY, TFS, and RFS have no effect. Note that writes to reserved bits
are ignored and reads to those bits return zeros.
Register Name:
SSSR
Block
Base Address:
0xC801_20
Offset Address
0x08
Reset Value
0x0000_0000
Register Description:
SSP Status Register
Access:
(See below.)
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
8
7
6
5
4
3
2
1
0
Reserved
RFL
TFL
ROR
RFS
TFS
BS
Y
RNE
TNF
Rsvd.
Register
SSSR (Sheet 1 of 2)
Bits
Name
Description
Reset Value
Access
31:16
(Reserved)
(Reserved)
0x0000
RV
15:12
RFL
Receive FIFO Level:
Number of entries minus one in Receive FIFO.
Note:
When the value 0xF is read, the FIFO is either empty or
full and the programmer should refer to the RNE bit.
0000
RO
11:08
TFL
Transmit FIFO Level:
Number of entries in Transmit FIFO.
Note:
When the value 0x0 is read, the FIFO is either empty or
full and the programmer should refer to the TNF bit.
0000
RO
7
ROR
Receive FIFO Overrun:
0 = Receive FIFO has not experienced an overrun
1 = Attempted data write to full Receive FIFO, request interrupt
0
RW
6
RFS
Receive FIFO Service Request:
0 = Receive FIFO level is below RFT threshold, or SSP disabled.
1 = Receive FIFO level is at or above RFL threshold, request
interrupt
0
RO
5
TFS
Transmit FIFO Service Request:
0 - Transmit FIFO level exceeds TFT threshold, or SSP disabled
1 - Transmit FIFO level is at or below TFL threshold, request
interrupt
0
RO