Intel debug port for Atom

How to debug an Atom processor over JTAG?

Official presentation of the "Intel JTAG debugger" is [1].

The standard Intel debug port is the 60-pin XDP (eXtended Debug Port). It extends JTAG with additional signals. This port also has a lower pin count variant: the 31-pin XDP-SSA (Second Side Attach, designed to be on the other side of the board, where there are less components), and an even lower pin count variant: the 24-pin flex edge connector XDP-SFF-24. See [2] for a comparison among other debug ports (e.g., ARM, Nexus, ...). See [3] for guidelines regarding the physical layout of the XDP port. XDP pinout on page 23.

XDP includes an I²C line for SMB (System Management Bus).

XDP includes one or several observation ports (OBSFN_*, previously named "Breakpoint Monitor" BPM). Four are availables on the stardard 60-pin XDP, while only one is available on the 31-pin XDP-SSA.

Finding a dev. board with XDP access

The MinnowBoard features an Intel Atom Bayrail SoC processor ready to support Yocto Linux projects. See [4]. An improved version can be bought there [5]. The "High Speed Expansion Connector" gives access to some XDP lines such as the JTAG port and one observation port. There is even a breakout board (names "Lure" in this project) to route the signals to a more standard XDP connector, see [6].

Functionalities of Intel on-chip debug

The documentation of the Lauterbach debugger for Intel x86/x64 [7] gives a list of many available functionalities. See [8] and [9] for details regarding traces.