4.2.1. JTAG direct to core access

Maintaining the existing access mechanism of a SoC has the following advantages:

Because this method of access goes through the core, it provides any native memory address translations from virtual to physical. It has the disadvantages that it requires an understanding of how the core accesses memory, and might also take several cycles depending on the instruction set.

Figure 4.1 shows an external JTAG connection connected to some memory through a processor.

Figure 4.1. JTAG connection

To view this graphic, your browser must support the SVG format. Either install a browser with native support, or install an appropriate plugin such as Adobe SVG Viewer.


External tools connected through the JTAG link can access the system memory by instructing the processor, in Halted-Debug Mode, to fetch and save values from the memory directly. This method permits the automatic translation of the Virtual Modified Address (VMA) that the core sees, to the physical memory addressing of the system.

Copyright © 2004, 2007, 2010 ARM Limited. All rights reserved.ARM DGI 0012D
Non-ConfidentialID062610