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DS-5 cannot connect to or auto-detect a target system with a very slow JTAG/SWD clock

Article ID: 103488920

Published date: 21 Sep 2017

Last updated: -

Applies to: DSTREAM, DS-5 Development Studio, ULINK Family


Why can't DS-5 connect to or detect a target system with a very slow JTAG/SWD clock ?


If an attempt to connect DS-5 to a very slow target system is failing, then there are 2 timeouts that may be an issue :

  1. timeout between the host debugger (DS-5) and JTAG/SWD interface unit, and

  2. low-level JTAG timeouts when accessing an ARM core.


A DSTREAM unit can connect to devices running at very low speed (down to ~13 Hz). If you are having problems connecting to or debugging a slow system (for example, a hardware emulation platform), first ensure that you have installed the latest DSTREAM firmware. The firmware is included within the DS-5 installation.


For (1), you can configure the duration of the DS-5 - DSTREAM communications timeout by adding the environment variable SCC_TIMEOUT, which specifies a timeout in milliseconds, and setting this to 10000000.

This effectively means there are no timeouts between the host and debug hardware vehicle. You must set this environment variable before you start DS-5.


For (2), the DSTREAM firmware provides the option to disable JTAG timeouts per core.

This is provided by setting the option  "JTAG Timeouts Enabled" to 'False' within the Platform Configuration Editor (PCE) tool in DS-5 on each core that you intend to connect to.

By default this option is set, but it can be cleared to disable DSTREAM hardware timeouts.

After you change this option within PCE, you must rebuild the platform in order for the changes to be picked up.

Please see the example option on the Cortex-A57 below :



 The information in this article may also help you connect via VSTREAM to a CoreSightTM design running on a simulation or emulation platfom. In this case, 'VSTREAM' replaces references to DSTREAM units.



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