JTAG over the internet!

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.

(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)

The solution

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

The implementation

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

IEEE1149.1 Compliant JTAG

Controller

TAP

Device Under Test

TAP

TMS, TCK, TDI, TDO

GNDWorkstation

USB, ISA, PCI, PXI...

Boundary Scan Test Control SW

Test Vectors Transmit/Receive

Control HW

JTAG compliant devices

LAN, WAN, WLAN, LON,

CAN, FireWire, Internet

IEEE1149.1Compliant JTAG

Controller

TAP

Device Under Test

(DUT)

TAP

Uplink DownlinkPC

WorkstationUSB, ISA, PCI, PXI...

Asynchronous Transmission Path

Data Transceiving

Downlink TransceiverUplink Transceiver

TCK

TMS

TDI

0

0

1

0

0

1

1

0

TMS

TDI

0 0 1 0

TM

S

TD

I

TM

S

TD

I

1 0

TM

S

TD

I

TM

S

TD

I

0 1 0 1DataPacket

0

0

1

0

0

1

1

0

0 0 1 0

TM

S

TD

I

TM

S

TD

I1 0

TM

S

TD

I

TM

S

TD

I

0 1 0 1

LocalTCK

TMS

TDI

TMS

TDI

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.

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 won’t arrive to controller on time!

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)

(Example continued)

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

The solution: Virtual cells!

“Virtual Cells” are added to the end of Boundary-

Scan Chain Additional time is gained for

compensating transmission delays

25

5

20

1510

30

TDI

1TDO

DUT

v1 v5 v10

v15v20

25

5

20

1510

30

TDI

DUT

TDOFIFO

Control

Virtual Cell

Counter

JTAG Controller sees the BS chain like this: The real hardware looks like this:

11010..001011010..0010

1

Part of Uplink

Transmission link

Virtual BS-Cells that exist only logically

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!

(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 < alpha < 1)

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)

TAP

TCK

TMS

Downlink Transceiver

TDO

TDITDI_out

TDO_inRxTx

COMTransceivere.g. UART

TMS

TDI

TDO

ASIC Boundary Scan Chain

COM

Optional External

TAPA

SIC

Bo

un

da

ry

Sc

an

Ch

ain

1149.1 FSM

ASIC

PerformanceUsing 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.

Possible uses

Board Under Test(BUT)

TAP

InternalLogicDown

link

Board Under Test(BUT)

TAP

InternalLogicDown

link

Board Under Test(BUT)

TAP

InternalLogicDown

link

Bridge

Backplane System Test

NetworkedTargets

On-Site Targets

High Speed Manufacturing

AdaptedMedia Link

Ext.SwitchCtrl

Workstation UplinkTAP

High Speed Interface

LAN, WAN, WLAN, LON, CAN, FireWire, RS-232, RS-422, RS-485, GSM, IrDA,

Echelon, Profibus, TCP/IP, USB, WUSB, BlueTooth, Internet

Test-Mode switching with communication protocol

Asynchronous Transmission Path

Board Under Test(BUT)

TAP

I/F

InternalLogicDown

link

Board Under Test(BUT)

TAP

I/F

InternalLogicDown

link

Board Under Test(BUT)

TAP

I/F

InternalLogicDown

link

Board Under Test(BUT)

TAP

I/F

InternalLogicDown

link

Board Under Test(BUT)

TAP

InternalLogicDown

link

Proprietary Link

I/F

Router

TAP

IEEE1149.1 Compliant JTAG

Controller

USB, ISA,

PCI, PXI...

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

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

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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