LM3S9B81 Datasheet, PDF (91/1155 Pages) Texas Instruments – Stellaris® LM3S9B81 Microcontroller

Stellaris® LM3S9B81 Microcontroller
5.3.4.3
5.3.4.4
Recovering a "Locked" Microcontroller
Note:
Performing the sequence below restores the nonvolatile registers discussed in “Nonvolatile
Register Programming” on page 205 to their factory default values. The mass erase of the
Flash memory caused by the sequence below occurs prior to the nonvolatile registers being
restored.
If software configures any of the JTAG/SWD pins as GPIO and loses the ability to communicate
with the debugger, there is a debug sequence that can be used to recover the microcontroller.
Performing a total of ten JTAG-to-SWD and SWD-to-JTAG switch sequences while holding the
microcontroller in reset mass erases the Flash memory. The sequence to recover the microcontroller
is:
1. Assert and hold the RST signal.
2. Perform steps 1 and 2 of the JTAG-to-SWD switch sequence on the section called “JTAG-to-SWD
Switching” on page 92.
3. Perform steps 1 and 2 of the SWD-to-JTAG switch sequence on the section called “SWD-to-JTAG
Switching” on page 92.
4. Perform steps 1 and 2 of the JTAG-to-SWD switch sequence.
5. Perform steps 1 and 2 of the SWD-to-JTAG switch sequence.
6. Perform steps 1 and 2 of the JTAG-to-SWD switch sequence.
7. Perform steps 1 and 2 of the SWD-to-JTAG switch sequence.
8. Perform steps 1 and 2 of the JTAG-to-SWD switch sequence.
9. Perform steps 1 and 2 of the SWD-to-JTAG switch sequence.
10. Perform steps 1 and 2 of the JTAG-to-SWD switch sequence.
11. Perform steps 1 and 2 of the SWD-to-JTAG switch sequence.
12. Release the RST signal.
13. Wait 400 ms.
14. Power-cycle the microcontroller.
ARM Serial Wire Debug (SWD)
In order to seamlessly integrate the ARM Serial Wire Debug (SWD) functionality, a serial-wire
debugger must be able to connect to the Cortex-M3 core without having to perform, or have any
knowledge of, JTAG cycles. This integration is accomplished with a SWD preamble that is issued
before the SWD session begins.
The switching preamble used to enable the SWD interface of the SWJ-DP module starts with the
TAP controller in the Test-Logic-Reset state. From here, the preamble sequences the TAP controller
through the following states: Run Test Idle, Select DR, Select IR, Test Logic Reset, Test Logic
Reset, Run Test Idle, Run Test Idle, Select DR, Select IR, Test Logic Reset, Test Logic Reset, Run
Test Idle, Run Test Idle, Select DR, Select IR, and Test Logic Reset states.
June 29, 2010
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Texas Instruments-Advance Information