Difference between revisions of "EJTAG"

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(New page: EJTAG is an extension of IEEE 1149.1, the Joint Test Action Group. Allows interfacing with additional logic in SoC * direct control of processor for step-by-step debugging * access to buss...)
 
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EJTAG is an extension of IEEE 1149.1, the Joint Test Action Group.
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EJTAG is a MIPS-specific extension of IEEE 1149.1, the Joint Test Action Group.
 
Allows interfacing with additional logic in SoC
 
Allows interfacing with additional logic in SoC
 
* direct control of processor for step-by-step debugging
 
* direct control of processor for step-by-step debugging
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** aids in [[debugging]]
 
** aids in [[debugging]]
 
** possible usage as additional peripheral data bus
 
** possible usage as additional peripheral data bus
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== Debugging ==
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Attempting to use GNU debugger [http://www.gnu.org/software/gdb/].  GDP uses its own Remote Serial Protocol (RDB) to communicate to remote targets.  This protocol could be used to communicate with the XINU backends through the current serial connection.  Although, this would require additions to XINU: communication with the GDB host; altering of exception handler to allow GDB to take control of target processor.
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The use of the EJTAG port on the WRT54-series routers gives the user hardware control of the processor, avoiding the need for strategically placed breakpoints and XINU interrupt subsystem modification.  Additionally, requests by the debugger for specicfic data can be aquired directly from registers.  The trick to this operation is software that can interpret commands from RDB into EJTAG signals to be sent through the host parallel port, and vice-versa.  An implementation of this interpreter can be found at [http://www.totalembedded.com/open_source/jtag/mips32_ejtag.php].  An example of a buffered cable is also available at this location.

Revision as of 18:30, 1 June 2007

EJTAG is a MIPS-specific extension of IEEE 1149.1, the Joint Test Action Group. Allows interfacing with additional logic in SoC

  • direct control of processor for step-by-step debugging
  • access to busses and registers
    • aids in debugging
    • possible usage as additional peripheral data bus


Debugging

Attempting to use GNU debugger [1]. GDP uses its own Remote Serial Protocol (RDB) to communicate to remote targets. This protocol could be used to communicate with the XINU backends through the current serial connection. Although, this would require additions to XINU: communication with the GDB host; altering of exception handler to allow GDB to take control of target processor. The use of the EJTAG port on the WRT54-series routers gives the user hardware control of the processor, avoiding the need for strategically placed breakpoints and XINU interrupt subsystem modification. Additionally, requests by the debugger for specicfic data can be aquired directly from registers. The trick to this operation is software that can interpret commands from RDB into EJTAG signals to be sent through the host parallel port, and vice-versa. An implementation of this interpreter can be found at [2]. An example of a buffered cable is also available at this location.