JTAG over the internet!

1. JTAG over the internet!

2. 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.

3. (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)

4. The solution • Harnessing the internet and various forms of communication to allow long distance testing!

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

6. 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.

7. 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!

8. 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)

9. (Example continued) • Assuming the propagation delay of the cable is 5ns/m, a maximum cable length of 10 metres can only be used!

10. The solution: Virtual cells! “Virtual Cells” are added to the end of Boundary- Scan Chain  Additional time is gained for compensating transmission delays

11. 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!

12. (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)

13. 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)

14. 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.

15. 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

16. 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

17. 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

18. Thanks for listening!