Entity: AxisToJtag

File: AxisToJtag.vhd

Diagram

Description

Title : JTAG Support

Company : SLAC National Accelerator Laboratory

Description: AXI stream to JTAG

This file is part of 'SLAC Firmware Standard Library'. It is subject to the license terms in the LICENSE.txt file found in the top-level directory of this distribution and at: https://confluence.slac.stanford.edu/display/ppareg/LICENSE.html. No part of 'SLAC Firmware Standard Library', including this file, may be copied, modified, propagated, or distributed except according to

the terms contained in the LICENSE.txt file.

Axi Stream to JTAG Protocol

This module implements a simple protocol for encoding XVC transactions over an AXI stream. Part of this is support for unreliable transport protocols (by means of a memory buffer and transaction IDs). Once the protocol header is processed the stream is delegated to the AxisToJtagCore module.

INCOMING STREAM

The incoming Stream consists of consecutive words of AXIS_WIDTH_G bytes, must be framed with 'TLAST' and is expected to have the following format :

Header Word [, Payload ]

The header word is defined as

[31:30] Protocol Version -- currently "00" [29:28] Command [27:00] Command-specific parameter(s)

Note that if the core is configured for a stream width (AXIS_WIDTH_G) > 4 then the header is padded up to the desired width, i.e., the paylod must be word-aligned.

Each command word is answered with a reply word on the outgoing stream (see below).

The following commands are currently defined:

 "00"  QUERY: request basic features such as word length, memory depth.
        Payload: NONE, i.e., TLAST should be asserted with this command.
  "01"  JTAG: shift jtag vectors. The vectors are shipped in the payload.        The parameter bits for this command are defined as follows:
        [27:20] Transaction ID; this is used when the core is configured                with MEM_DEPTH_G > 0 in order to support a non-reliable                transport.        [19:00] JTAG vector length (in bits). The payload must provide                2*ceil( length / AXIS_WIDTH_G ) words of TMS/TDI vector                data. I.e., the length refers to the length of a single                TMS or TDI vector.                !!!!!!!                 NOTE: the number in [19:00] encodes the actual number                       minus 1. E.g., a value of 0 transmits one TMS                       and one TDI bit. Two payload words are expected                       in this example.                !!!!!!!
        Payload: sequence of words from the TMS and TDI bit-vectors:
                TMS_WORD, TDI_WORD, TMS_WORD, TDI_WORD, ...
                Note that the user must format the stream accordingly                and therefore must be aware of the stream width. This                parameter is returned by the QUERY command.
                If the number of bits supplied does not fill the last                word then the relevant bits must be lsb/right-aligned                in the last word.
                TLAST must be asserted during the transmission of the                last TDI/payload word.

OUTGOING STREAM

The outgoing stream consists of consecutive words of AXIS_WIDTH_G bytes and is framed with 'TLAST'. Each reply has the following format:

Header Word [, Payload ]

The header word is defined as

[31:30] Protocol Version; if the user supplies an unsupported protocol version in the request header then the reply contains an error code (see below) and the protocol version in the reply is set to the supported version.

[29:28] Command -- the request command is returned unless an error occurred; in case of an error the command bits in the reply are:

       "10"  ERROR: An error was detected. The 8 least-significant bits              [7:0] contain an error code:              1: bad protocol version; the protocol version in the reply                 is set to the supported version.              2: bad/unsupported command code              3: truncated input stream (TLAST detected before the                 first TDI word was received). Note that a premature                 TLAST which is detected after the first TDI word                 does NOT flag an error but yields a truncated reply                 (less TDO words than requested by the number of bits).
        "00"  QUERY: the response to a QUERY command encodes information              in the command-specific bits:
             [ 3: 0] AXIS_WIDTH_G - 1. I.e., this field encodes the                     word size (minus one) used by the core. This information                     is important for formatting the stream.             [19: 4] MEM_DEPTH_G. Indicates how much memory (if any) was                     configured in words.             [27:20] TCK period. Encoded as
                                      200Mhz     1                        round{ log10( ------- ) --- 256 }                                       Ttck      4
                    With the special value 0 representing 'unknown'.
        "01"  JTAG: the response to a JTAG command is a sequence of              TDO words which form the TDO bit vector. The vector              stored in little-endian format (first bit of the vector              is the LSB of the first TDO word).              If the number of JTAG bits does not fill the last TDO              word completely then the relevant bits are right-              aligned.

RELIABILITY SUPPORT

If the transport mechanism contains unreliable segments with a potential for data loss then a simple retry mechanism is not suitable because JTAG operations are not necessarily idempotent. The core can be configured to use internal memory (MEM_DEPTH_C > 0) in which case it stores the last JTAG TDO response in memory. When the next JTAG command arrives the core inspects the 'transaction ID' field of the command and if it is identical with the ID submitted along with the previous transaction then the core detects a retried operation and does not actually execute it again on JTAG but plays back the stored TDO response to the requestor.

Generics

Generic name	Type	Value	Description
TPD_G	time	1 ns
AXIS_FREQ_G	real	0.0	Clock frequency in Hz. This information is used for computing the JTAG clock frequency which is sent as part of a QUERY reply. If unset (=0.0) then this will cause the XVC server (software) to always return the requested (and not the true) TCK frequency in the XVC 'settck' command.
AXIS_WIDTH_G	positive range 4 to 16	4	Width in bytes of the TDATA; this module does not support TKEEP nor resizing the I/O streams.
CLK_DIV2_G	positive	4	Half period of TCK in axisClk cycles. I.e., for a given TCK frequency set CLK_DIV2_G = round( AXIS_FREQ_G / TCK_FREQ / 2 );
MEM_DEPTH_G	natural range 0 to 65535	4	Depth of buffer memory (in units of words of width AXIS_WIDTH_G) Setting to zero disables memory.
MEM_STYLE_G	string	"auto"	Memory type inference (Vivado) - use 'auto', 'block' or 'distributed'

Ports

Port name	Direction	Type	Description
axisClk	in	sl
axisRst	in	sl
mAxisReq	in	AxiStreamMasterType
sAxisReq	out	AxiStreamSlaveType
mAxisTdo	out	AxiStreamMasterType
sAxisTdo	in	AxiStreamSlaveType
tck	out	sl	JTAG
tdi	out	sl
tms	out	sl
tdo	in	sl

Signals

Name	Type	Description
r	RegType
rin	RegType
s	CombSigType
bufMem	MemType	buffer memory
memOut	slv(WORD_SIZE_C - 1 downto 0)	memory readout port

Constants

Name	Type	Value	Description
WORD_SIZE_C	positive	8*AXIS_WIDTH_G
ADDR_ZERO_C	AddrType	(others => '0')
LOCL_OSTRM_PORT	natural	0	Stream selector port indices
JTAG_OSTRM_PORT	natural	1
TCK_FREQ_REF_C	real	2.0E+8
TCK_FREQ_C	real	ite( AXIS_FREQ_G = 0.0, TCK_FREQ_REF_C, AXIS_FREQ_G/(2.0*real(CLK_DIV2_G)) )
TCK_LOG_RAT_C	real	ieee.math_real.log10( TCK_FREQ_REF_C / TCK_FREQ_C )
TCK_BITS_C	natural range 0 to 255	natural( ieee.math_real.round( TCK_LOG_RAT_C * 256.0/4.0 ) )
REG_INIT_C	RegType	( state => IDLE_S, nstate => IDLE_S, replyData => AXI_STREAM_MASTER_INIT_C, tLastSeen => '0', ackInput => '0', passTdo => '0', passTdi => '0', ridx => ADDR_ZERO_C, widx => ADDR_ZERO_C, memValid => false, xid => (others => '0') )

Types

Name	Type	Description
MemType
StateType	(IDLE_S, SEND_REP_S, WAIT_STARTED_S, WAIT_HDR_READY_S, WAIT_STOPPED_S, REPLAY_S)	one guard bit
RegType		State Record
CombSigType		group signals so it's easier not to forget one in the combinatorial sensitivity list…

Functions

xidIsNew ( data : in slv;
xid : in XidType;
memValid : in boolean ) return boolean

checkLen ( data : in slv ) return boolean

setQueryData ( wordLength : in natural range 4 to 16;
memDepth : in natural range 0 to 65535;
data : inout slv ) return ()

sendHeaderNow ( v : inout RegType ) return ()

Processes

P_MUX_TDI: ( r, mAxisReq, s )

Description
Control flow of the input stream to the AxisToJtagCore. We stop the flow while inspecting the header or during playback from memory (when we discard the input stream)

P_TKEEP: ( s )

Description
output stream; splice in TKEEP

P_COMB: ( r, mAxisReq, sAxisTdo, s, memOut )

P_SEQ: ( axisClk )

Instantiations

U_MUX: surf.AxiStreamSelector

Description
A stream multiplexer; depending on 'sel' either Ib(0) or Ib(1)
is routed to Ob.
We use this to splice locally generated info (reply header and
memory playback data) into the output stream.

U_JTAG: surf.AxisToJtagCore

Description
The core which does all the JTAG work (while this module deals with
the protocol and housekeeping.