J-Link / J-Trace User Guide (UM08001) - Microcontrollers

If you experience problems with a particular device, do not hesitate to contact Segger.
7.5.1 LPC
7.5.1.1 Fast GPIO bug
The values of the fast GPIO registers can not be read direct via JTAG from a debugger.
The direct access to the registers corrupts the returned values. This means that
the values in the fast GPIO registers normally can not be checked or changed from a
debugger.
Solution / Workaround
J-Link supports command strings which can be used to read a memory area indirect.
Indirectly reading means that a small code snippet will be written into RAM of the
target device, which reads and transfers the data of the specified memory area to the
debugger. Indirectly reading solves the fast GPIO problem, because only direct register
access corrupts the register contents.
Define a 256 byte aligned area in RAM of the LPC target device with the J-Link command
map ram and define afterwards the memory area which should be read indirect
with the command map indirectread to use the indirectly reading feature of J-Link.
Note that the data in the defined RAM area is saved and will be restored after using
the RAM area.
This information is applicable to the following devices:
• LPC2101
• LPC2102
• LPC2103
• LPC213x/01
• LPC214x (all devices)
• LPC23xx (all devices)
• LPC24xx (all devices)
Example
J-Link commands line options can be used for example with the C-SPY debugger of
the IAR Embedded Workbench. Open the Project options dialog and select Debugger.
Select Use command line options in the Extra Options tap and enter in the
textfield --jlink_exec_command "map ram 0x40000000-0x40003fff; map indirectread
0x3fffc000-0x3fffcfff; map exclude 0x3fffd000-0x3fffffff;" as shown
in the screenshot below.
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