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 specifications

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.

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

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)

Performance Using a 1 Gigabit Ethernet connection makes it possible to execute boundary-scan tests on the target design at acceptable TCK frequencies of up to 40MHz over an unlimited distance.

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

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