Altera Arria V Avalon-ST Manual de usuario Pagina 51

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Table 4-4: 64- or 128Bit Avalon-ST TX Datapath
Signal Direction Description
tx_st_data[<n>-1:0]
Input Data for transmission. Transmit data bus. Refer to the following
sections on data alignment for the 64- and 128-bit interfaces for
the mapping of TLP packets to tx_st_data and examples of the
timing of this interface. When using a 64-bit Avalon-ST bus, the
width of tx_st_d ata is 64. When using a 128-bit Avalon-ST
bus, the width of tx_st_data is 128 bits. The Application Layer
must provide a properly formatted TLP on the TX interface. The
mapping of message TLPs is the same as the mapping of Transac‐
tion Layer TLPs with 4 dword headers. The number of data
cycles must be correct for the length and address fields in the
header. Issuing a packet with an incorrect number of data cycles
results in the TX interface hanging and becoming unable to
accept further requests.
<n> = 64 or 128.
tx_st_sop
Input Indicates first cycle of a TLP when asserted together with tx_st_
valid.
tx_st_eop
Input Indicates last cycle of a TLP when asserted together with tx_st_
valid.
tx_st_ready Output Indicates that the Transaction Layer is ready to accept data for
transmission. The core deasserts this signal to throttle the data
stream. tx_st_ready may be asserted during reset. The Applica‐
tion Layer should wait at least 2 clock cycles after the reset is
released before issuing packets on the Avalon-ST TX interface.
The reset_status signal can also be used to monitor when the
IP core has come out of reset.
If tx_st_ready is asserted by the Transaction Layer on cycle
<n> , then <n + readyLatency> is a ready cycle, during which
the Application Layer may assert valid and transfer data.
When tx_st_ready, tx_st_valid and tx_st_data are
registered (the typical case), Altera recommends a readyLa-
tency of 2 cycles to facilitate timing closure; however, a
readyLatency of 1 cycle is possible. If no other delays are added
to the read-valid latency, the resulting delay corresponds to a
readyLatency of 2.
4-14
Avalon-ST TX Interface
2014.12.15
Altera Corporation
Interfaces and Signal Descriptions
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