JTAG over the internet!

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JTAG over the internet!
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The problem

• Until now device testing was physically
  (geographically) limited as the DUT (device under
  test) and the TAP controller had to be located in
  close proximity.

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(continue)

• This may be problematic when devices are
  Inaccessible due to various reasons such as
  geographical distance (different states / outer
  space) or After having been deployed (logistical
  and financial considerations)

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The solution

• Harnessing the internet and various forms of
  communication to allow long distance testing!

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The implementation

• Simulation of direct connectivity both
  controller and DUT believe they are directly
  connected and communicate with IEEE-1149.1
  specifications

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Data Transceiving
TMS-TDI Information is sent from Uplink to
Downlink. TCK is generated by the Downlink,
asynchronously to original. TDO information is
sent from Downlink to Uplink.
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Delay Compensation

• Boundary scan relies on synchronous
  communication. This is a potential problem as
  propagation delays become significant over large
  distances ? data from last link in BS chain wont
  arrive to controller on time!

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Example

• If for example, the target TCK frequency is
  10MHz, which equates to a TCK clock period of 100
  ns. This effectively, only leaves a period of 50
  ns for TDO data to travel from the last DUT in
  the chain to the test controller. (1/2 cycle)

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(Example continued)

• Assuming the propagation delay of the cable is
  5ns/m, a maximum cable length of 10 metres can
  only be used!

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The solution Virtual cells!

• Virtual Cells are added to the end of Boundary-
• Scan Chain ? Additional time is gained for
• compensating transmission delays

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Session management

• Since the number of virtual cells is a function
  of the communication line congestion (and thus
  delay) which varies with time, the number of
  virtual cells should change with time as well!

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(continue)

• A connection oriented (TCP like) session is
  established between uplink and downlink and
  channel loop-back tests are performed to
  calculate the optimum number of virtual cells,
  using EMWA

(Where X(k) is the estimation at time k and
0 lt alpha lt 1)
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Embedded implementation

• Both uplink and downlink units can be embedded
  onto the chip allowing for smaller packaging
  (which is of high importance for small
  proportioned devices)

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Performance
Using a 1 Gigabit Ethernet connection makes
itpossible to execute boundary-scan tests on the
targetdesign at acceptable TCK frequencies of up
to40MHz over an unlimited distance.
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Possible uses

• Factory with multiple production lines - Often
  a manufacturing facility will have multiple
  production lines this will centralize
  testing and may dramatically reduce costs

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Some more uses

• Testing performed on devices orbiting the earth
  where the only means of communication is unwired
• Cellular phones testing / firmware updates
• Configurations and contingency operations remotely

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Benefits (conclusion)

• Late test access and SW/FW updates possible
• Real time diagnostics made possible from one,
  remote place
• Enable access to otherwise inaccessible devices
• Scalable

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Thanks for listening!