Altera Embedded Peripherals IP Manual do Utilizador Página 183

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Figure 18-2: System with a JTAG to Avalon Master Bridge Core
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Rest of the
System
Host
PC
Altera FPGA
JTAG to Transaction Bridge
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A
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alon-ST
Bytes to
Packets
Con
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src
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Avalon-ST
Packets to
Transactions
Converter
Avalon-MM
src
Avalon-ST
Source
sink
Avalon-ST
Sink
src
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s
Avalon-ST
Single Clock
FIFO
(64 bytes)
src
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A
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Pa
ckets to
Bytes
Con
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Avalon-ST
JTAG
Interface
Core
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JTAG
Clock
JTAG
Clock
System
Clock
The SPI Slave to Avalon Master Bridge and the JTAG to Avalon Master Bridge cores accept encoded
streams of bytes with transaction data on their respective physical interfaces and initiate Avalon-MM
transactions on their Avalon-MM interfaces. Each bridge consists of the following cores, which are
available as stand-alone components in Qsys:
Avalon-ST Serial Peripheral Interface and Avalon-ST JTAG Interface—Accepts incoming data in
bits and packs them into bytes.
Avalon-ST Bytes to Packets Converter—Transforms packets into encoded stream of bytes, and a
likewise encoded stream of bytes into packets.
Avalon-ST Packets to Transactions Converter—Transforms packets with data encoded according to
a specific protocol into Avalon-MM transactions, and encodes the responses into packets using the
same protocol.
Avalon-ST Single Clock FIFO—Buffers data from the Avalon-ST JTAG Interface core. The FIFO is
only used in the JTAG to Avalon Master Bridge.
For the bridges to successfully transform the incoming streams of bytes to Avalon-MM transactions,
the streams of bytes must be constructed according to the protocols used by the cores.
The following example shows how a bytestream changes as it is transferred through the different layers
in the bridges.
Figure 18-3: Bits to Avalon-MM Transaction
00 00 00 047A 7C 00 02 4B 5A 407D 6A FF 03 5F7B4A 4A 4A 4D
00 00 00 04 02 4B 7A 40 4A FF 03 5F
Comma nd Addres s Data
Writes four bytes of data (4A, FF, 03 an d
5F) to address 0x024 B7A40
Packet Layer
Input: Bytes
Outp ut: Ava lon-ST
Packet s
Trans action Layer
Inp ut: Ava lon-ST
Pack ets
Output: Avalon-MM
Tran saction
00 00 00 047A 7C 00 02 4B 5A 407D 4A FF 03 5F7B
LSB
MSB
Idle Idle Idle Esca pe
Dropp ed
Esca pe is droppe d.
Next byte is XORe d
with 0x20.
Phys ical Layer
Input: Bits
Output: Bytes
SO P Ch 0 Escap e
Esc ape is dropped.
Next byte is XORed
with 0x20.
EOP
Bytes ca rried over
the physical interface
after idles and esc apes
have been inse rted.
The p acket enc oded
as byt e s.
The trans ac tion
en caps ulated as a
pack et.
The Avalon-MM
transact ion.
18-2
Functional Description
UG-01085
2014.24.07
Altera Corporation
SPI Slave/JTAG to Avalon Master Bridge Cores
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