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Hardware Reference Manual 271
Intel
®
IXP2800 Network Processor
Media and Switch Fabric Interface
8.3.4.1 SPI-4
FIFO status information is sent periodically over the TSTAT signals from the PHY to the Link
Layer device, which is the IXP2800 Network Processor. (The RXCDAT pins can act as TSTAT
based on the MSF_Tx_Control[TSTAT_Select] bit.) The FIFO status of each port is encoded in a
2-bit data structure — code 0x3 is used for framing the data, and the other three codes are valid
status values, which are interpreted by Microengine software.
The FIFO status words are received according to a repeating calendar sequence. Each sequence
begins with the framing code to indicate the start of a sequence, followed by the status codes,
followed by a DIP-2 parity code covering the preceding frame. The length of the calendar, as well
as the port values, are defined in this section, and shown in Figure 96.
Tx_Port_Status_# is a register file containing 256 registers, one for each of the SPI-4.2 ports. The
port status is updated each time a new calendar status is received for each port, according to the
mode programmed in MSF_Tx_Control[Tx_Status_Update_Mode]. The Tx_Port_Status_#
register file holds the latest received status for each port, and can be read by CSR reads.
There are 16 Tx_Multiple_Port_Status_# registers. Each aggregates the status for each group of
16 ports. These registers provide an alternative method for reading the FIFO status of multiple
ports with a single CSR read. For example, Tx_Multiple_Port_Status_0 contains the 2-bit status
for ports 0 – 16, and provides the same status as reading the individual registers,
Tx_Port_Status_0 through Tx_Port_Status_15.
Figure 96. Tx Calendar Block Diagram
A9761-02
Tx_Calendar_Length
Calendar Counter
8
256
TSTAT
CSR
Reads
CSR
Reads
To
MSF_Interrupt_Status
and MSF_Tx_Control
Registers
Parity
Start of
Frame
Detect
Frame
Pattern
Counter
Tx
Port
Status
256
2
Tx
Multiple
Port
Status
16
32
Tx_Calendar