ARM Technical Support Knowledge Articles

DS-5 cannot connect to a core with a very slow clock / Can I stop the core clock when debugging with RVI/DSTREAM units ?

Applies to: DS-5, DSTREAM, RealView ICE and Trace (RVI / RVT)


DSTREAM / RVI units support connecting to devices running at very low speed (down to ~13 Hz). If you are having problems connecting to or debugging a slow core, please upgrade to the latest DSTREAM / RVI firmware as shipped with your tools installation. 

DSTREAM / RVI software includes an option "JTAG Timeouts Enabled" in the 'Device Properties' window of the 'Debug Hardware Config' (formerly RVConfig) application. By default this option is set, but it can be cleared to disable DSTREAM / RVI hardware timeouts. If you clear this option when DSTEAM / RVI is configured in adaptive mode, RTCK can be stopped without DSTREAM / RVI reporting an error.

The advice contained in this article may also assist when connecting via VSTREAM to a CoreSighttm design running on a simulation or emulation platfom. In this case, 'VSTREAM' replaces references to DSTREAM and/or RVI units.

There is also a timeout that operates between the host debugger (DS-5) and the debug hardware device (DSTREAM/RVI unit). This timeout may be triggered if you have already disabled 'JTAG Timeouts Enabled' as described above.

You can configure the duration of this DS-5 - DSTREAM timeout by adding the environment variable SCC_TIMEOUT, which specifies a timeout in milliseconds.

When working with very slow targets (less than 1KHz), both the DSTREAM / RVI and DS-5 timeouts should be disabled, so you need to do all the following:

  • Configure DSTREAM / RVI in adaptive mode and provide RTCK
  • Disable the option "JTAG Timeouts Enabled" in Debug Hardware Config
  • Set SCC_TIMEOUT with a very large value (for example, if you set it to 10000000 you can forget totally about timeouts)

Note that auto-configuration is unlikely to work with a very slow core clock, so you may need to select the core template in Debug Hardware Config manually.

Article last edited on: 2014-08-29 15:25:48

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