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Xtensa JTAG stuff (yeah)
=== DWM-W015 ===
=== DWM-W015 ===
http://www.flickr.com/photos/micahdowty/3846960965/sizes/o/in/photostream/
[http://www.flickr.com/photos/micahdowty/3846960965/sizes/o/in/photostream/ Image source]
[[Image:Dwm-w015-scanlime.jpg|800px]]
=== DWM-W015A ===
=== DWM-W015A ===
[[Image:Dwm-w024.jpg|800px]]
[[Image:Dwm-w024.jpg|800px]]
== Debugging the Ath6k Xtensa CPU ==
In case you want to run your own code on it (and subsequently need to debug it), the Atheros chip has two debug facilities: UART and JTAG. UART is a simple serial connection for printf-debugging, while JTAG can be used for single-stepping, breakpoints, etc.
'''NOTE THAT BOTH UART AND JTAG USE 1.8V LOGIC LEVELS. DO NOT DRIVE WITH 3.3 OR 5.0 V!!!'''
=== UART ===
Serial communication on the Xtensa side can be done as [https://problemkaputt.de/gbatek-dsi-atheros-wifi-internal-i-o-00c000h-serial-uart-hw2-hw4-hw6.htm described in GBATEK]. On the DWM-W015, the UART testpoints appear on the bottom side of the PCB, near the edge (see below). On the DWM-W024, RX and TX are probably one of the four testpoints on the top side (see above).
[[Image:Dwm-w015-bottom-marked.jpg|400px]]
=== JTAG ===
The four primary JTAG pins are exposed on the connector to the main board. However, the AR6002 has two extra pins that control JTAG functionality: JTAG_nRST and EJTAG_RST. They are marked in the image below, and they work as follows:
* '''JTAG_nRST''' resets the CPU core when pulled low. Some debuggers use this signal.
* '''EJTAG_RST''' is latched on chip powerup. If high, after a 'system' reset (read: the nWIFI_RST on the connector is pulled low), the Xtensa CPU is held at reset until JTAG_nRST is brought high. If EJTAG_RST is low, nothing special happens.
Thus, if your debugger has a JTAG_nRST signal (and you want to use it), pull EJTAG_RST to VDD18, and connect JTAG_nRST to your debugger. Otherwise, pull EJTAG_RST to ground (or leave it floating as-is, it probably has an internal pulldown).
As debugger, OpenOCD (or its fork for the ESP32) and any JTAG dongle compatible with it should work. '''Note that all JTAG communications use 1.8V! Using a higher voltage will kill the AR6002!'''
[[Image:Dwm-w015-top-marked.jpg|400px]]
=== DWM-W024 testpoints ===
The DWM-W024 has four testpoints with currently-unknown functionality. These are probably UART TX, UART RX, JTAG_nRST, and EJTAG_RST. However, which testpoint is which signal is not yet known.
== Documents and external links ==
== Documents and external links ==