+++ /dev/null
-Debugging hardware can be tricky especially when doing kernel and drivers
-development. It might become handy for you to add serial console to your
-device as well as using JTAG to debug your code.
-
-\subsection{Adding a serial port}
-
-Most routers come with an UART integrated into the System-on-chip
-and its pins are routed on the Printed Circuit Board to allow
-debugging, firmware replacement or serial device connection (like
-modems).
-
-Finding an UART on a router is fairly easy since it only needs at
-least 4 signals (without modem signaling) to work : VCC, GND, TX and
-RX. Since your router is very likely to have its I/O pins working at
-3.3V (TTL level), you will need a level shifter such as a Maxim MAX232
-to change the level from 3.3V to your computer level which is usually
-at 12V.
-
-To find out the serial console pins on the PCB, you will be looking
-for a populated or unpopulated 4-pin header, which can be far from
-the SoC (signals are relatively slow) and usually with tracks on
-the top or bottom layer of the PCB, and connected to the TX and RX.
-
-Once found, you can easily check where is GND, which is connected to
-the same ground layer than the power connector. VCC should be fixed
-at 3.3V and connected to the supply layer, TX is also at 3.3V level
-but using a multimeter as an ohm-meter and showing an infinite
-value between TX and VCC pins will tell you about them being different
-signals (or not). RX and GND are by default at 0V, so using the same
-technique you can determine the remaining pins like this.
-
-If you do not have a multimeter a simple trick that usually works is
-using a speaker or a LED to determine the 3.3V signals. Additionnaly
-most PCB designer will draw a square pad to indicate ping number 1.
-
-Once found, just interface your level shifter with the device and the
-serial port on the PC on the other side. Most common baudrates for the
-off-the-shelf devices are 9600, 38400 and 115200 with 8-bits data, no
-parity, 1-bit stop.
-
-\subsection{JTAG}
-
-JTAG stands for Joint Test Action Group, which is an IEEE workgroup
-defining an electrical interface for integrated circuit testing and
-programming.
-
-There is usually a JTAG automate integrated into your System-on-Chip
-or CPU which allows an external software, controlling the JTAG adapter
-to make it perform commands like reads and writes at arbitray locations.
-Additionnaly it can be useful to recover your devices if you erased the
-bootloader resident on the flash.
-
-Different CPUs have different automates behavior and reset sequence,
-most likely you will find ARM and MIPS CPUs, both having their standard
-to allow controlling the CPU behavior using JTAG.
-
-Finding JTAG connector on a PCB can be a little easier than finding the
-UART since most vendors leave those headers unpopulated after production.
-JTAG connectors are usually 12, 14, or 20-pins headers with one side of
-the connector having some signals at 3.3V and the other side being
-connected to GND.
projects / openwrt / staging / wigyori.git / blobdiff