Altera Embedded Peripherals IP - Manual (Page 186)

Interfaces
Table 19-1: Properties of Avalon-ST Interfaces
Feature Property
Backpressure Ready latency = 0.
Data Width
Data width = 8 bits; Bits per symbol = 8.
Channel Supported, up to 255 channels.
Error Not used.
Packet Supported only on the Avalon-ST Bytes to Packet Converter
core’s source interface and the Avalon-ST Packet to Bytes
Converter core’s sink interface.
For more information about Avalon-ST interfaces, refer to the Avalon Interface Specifications .
Operation—Avalon-ST Bytes to Packets Converter Core
The Avalon-ST Bytes to Packets Converter core receives streams of bytes and transforms them into
packets. When parsing incoming bytestreams, the core decodes special characters in the following
manner, with higher priority operations listed first:
• Escape (
0x7d
)—The core drops the byte. The next byte is XORed with
0x20
.
• Start of packet (
0x7a
)—The core drops the byte and marks the next payload byte as the start of a
packet by asserting the
startofpacket
signal on the Avalon-ST source interface.
• End of packet (
0x7b
)—The core drops the byte and marks the following byte as the end of a packet by
asserting the
endofpacket
signal on the Avalon-ST source interface. For single beat packets, both the
startofpacket
and
endofpacket
signals are asserted in the same clock cycle.
• Channel number indicator (
0x7c
)—The core drops the byte and takes the next non-special character
as the channel number.
Figure 19-3: Examples of Bytestreams
0x7c 0x01 0x7a 0x7d 0x5 a 0x0 1 0xff 0x7b 0x3a ...
Ch a nn e l 1 SO P Da ta = 0x7a Data byte s EOP Las t
Da ta
byte
Singl e -c hann e l pack e t fo r Chann e l 1:
0x7c 0x02 0x7a 0x7b 0x3 a
Ch a nn e l 2 SO P EOP Da ta
byte
S ingl e -be at pack e t:
0x7c 0x00 0x7a 0x10 0x1 1 0x3 0 0x3 1 0x7b 0x14
Ch a nn e l 0 SO P
(Ch 0)
Da ta
(Ch 0)
EOP
(Ch 0)
Da ta
(Ch 0)
Inte rle aved channel s in a pack e t:
0x7 c 0x0 1 0x7 c 0x00 0x12 0x13
Ch a nnel 1 Da ta
(Ch 1)
Cha nnel 0 Dat a
(Ch 0)
19-2 Interfaces
UG-01085
2014.24.07
Altera Corporation Avalon-ST Bytes to Packets and Packets to Bytes Converter Cores
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