Parallel Data Formats For Buffer Storage; Buffer Operation - Intel IXP45X Developer's Manual

Intel
Table 272. National Microwire
SSP
_SC
LK
SSP
_SF
RM
SSP
_TX
D
SSP
_RX
D
SSP
_SC
LK
SSP
_SF
RM
SSP
_TX Bit<0>
D
SSP
_RX
D
20.2.2

Parallel Data Formats for Buffer Storage

Data in buffers is always stored with one sample per 16-bit word regardless of the
format data word length. Within each 16-bit field, stored data sample is right-justified,
with word LSB in bit 0, and unused bits packed as zeroes on left-hand (MSB) side. Logic
in SSP automatically left-justifies data in the Transmit FIFO so that the sample is
properly transmitted on SSP_TXD in the selected frame format.
20.3

Buffer Operation

There are two separate and independent buffers for "incoming" (from peripheral) and
"outgoing" (to peripheral) serial data. Buffers are filled or emptied by an SRAM-like
transfer initiated by the system processor.
Although the system bus is 32 bits wide, only single samples may be transferred. Thus,
only the lower two bytes of the 32 bit word will have valid data; the upper two bytes
are not used and will include dummy or invalid data that should be discarded.
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Intel IXP45X and Intel IXP46X Product Line of Network Processors
Developer's Manual
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IXP45X and Intel IXP46X Product Line of Network Processors—Synchronous Serial Port
*
Frame Format
...
...
Bit<7> ... Bit<0>
8-Bit Control
...
1 Clk
Bit<N>
...
...
...
1 Clk
Bit<N> ...
4 to 16 Bits
Single Transfer
... ...
... ...
... Bit<7> ...
... Bit<0> ...
Continuous Transfers
Bit<0>
Bit<0>
1 Clk
Bit<N>
August 2006
Order Number: 306262-004US
...
...
...
... Bi