Background debug mode interface: Difference between revisions

Revision as of 14:37, 19 April 2014

Revision as of 14:39, 19 April 2014

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{{Cleanup|date=October 2009}}

'''Background Debugdebug Modemode''' (BDM) interface is an electronic interface that allows [[debugging]] of [[embedded system]]s. Specifically, it provides [[in-circuit emulator|in-circuit debugging]] functionality in microcontrollers. It requires a single wire and specialized electronics in the system being debugged.

It appears in many [[Freescalefreescale Semiconductorsemiconductor]] products.

The interface allows a ''Host'' to manage and query a ''Targettarget''. Specialized hardware is required in the target device. No special hardware is required in the host; a simple [[wikt:bidirectional|bi-directional]]biidirectional [[I/O port|I/O pin]] is sufficient.

== I/O signals ==

The signals used by BDM to communicate data to and from the target are initiated by the host processor. The host [[wiktionary:negates|negates]] the transmission line, and then either

* [[wiktionary:asserts|Asserts]] the line sooner, to output a 1,

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In other words the increasing complexity of today’s software and hardware designs is leading to some fresh approaches to debugging. ''Silicon manufacturers offer more and more on-chip debugging features for emulation of new processors''.

This capability, implemented in various processors under such names as Backgroundbackground Debugdebug Modemode (BDM), [[Joint Test Action Group|JTAG]] and on-chip [[In-circuit emulator|in-circuit emulation]], puts basic debugging functions on the chip itself. With a BDM (1 wire interface) or JTAG (standard JTAG) [[debug port]], you control and monitor the microcontroller solely through the stable on-chip debugging services.

This debugging mode runs even when the target system crashes and enables developers to continue investigating the cause of the crash.

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== BDM functions ==

Depending on the target part, the BDM controller may feature a hardware [[breakpoint]] register. The register holds a value indicating an [[memory address|address]] in memory. When the target part's CPU accesses that ___location in memory, the BDM hardware can take control of the target part, stop program execution, and begin operating in Backgroundbackground Modemode.

== References ==