I have posted this question in the TM4C forum, and it was suggested that I also post here, as it may be a problem with the latest version of CCS.
I have been using the EK-TM4C1294XL Launchpad for several weeks with no problem. I am using Code Composer Studio 6.1.0.00104 for Linux, on a 32-bit Debian Linux system.
Today I went to reload my test code into the Launchpad, and I got the dreaded "CORTEX_M4_0: Error connecting to the target: Frequency is out of range" message.
The Launchpad *is* running. The previous test program outputs debug text through UART0, and I can see that text through the virtual com port on the debug interface. I attempted to load the "blinky" demo through CCS and that failed the same way. In desperation I rebooted my computer; that did not resolve the problem.
I have followed the procedure described in the "JTAG Communication Failures" post to unlock the debug port (using Uniflash instead of LMFlash, since I'm on a Linux system). That seemed to work ok, but when I relaunched CCS I still had the problem. I can successfully use Uniflash to load both the "blinky" demo and my own application program; it's only CCS that fails.
The *only* thing I can think of that has changed since last week, is that when I launched CCS today, I was informed that there were program updates available, and I accepted them. I'm worried that the latest updates to CCS have broken the debugger. For the time being I can use Uniflash for testing, but should I remove CCS and reinstall the original version?