ARM Technical Support Knowledge Articles

JTAG port on MPS internal Trace Mictor connector does not work

Applies to: MPS



The MPS box has a 20-way JTAG connector on the back panel for connecting a debug ICE unit. If real-time Trace is required, it is necessary to open up the enclosure and connect the TPA (Trace Port Analyzer) to the 38-way Mictor connector in the center of the FPGA daughter card. This Mictor includes a JTAG port, so in theory, when doing Trace, it is no longer necessary to plug the JTAG ICE into the MPS back panel as it can be connected to the Trace Mictor. For example, ARM's RealView Trace TPA has a probe header card with a Mictor plug and a 20-way box header so that the JTAG cable from the ICE can be "piggybacked" onto the Trace Mictor.

Problem technical description

There is an anomaly in the first revision of the MPS firmware that prevents the JTAG port on the internal Mictor from being used. When the MPS selects the JTAG port on the internal Mictor, the nTRST signal into the ARM Cortex-M3 CPU is left floating. This causes the nTRST input to oscillate and the JTAG interface is rendered unusable.


The problem can be fixed with an update to the system CPLD. Newer units will be shipped with the updated CPLD image. Older units that exhibit the problem can be returned to ARM's European repair center for reprogramming with the new CPLD image. It is not possible for the end user to reprogram the CPLD on site. If your MPS unit needs reprogramming, please complete our online board fault report form and we will arrange for the unit to be shipped back to our repair facility.


There is a simple workaround, and that is to continue using the rear panel 20-way JTAG connector when performing Trace on an MPS. The only reason to use the internal Mictor for JTAG is the convenience of having both ICE and Trace cables routed to the same place on the target board.

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