JTAG vs ISP, PDI, TPI and the like

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I've always used ISP, PDI or TPI, debugwire and the like for programming and debugging mega, tiny and xmega parts, but I'm curious, would there be advantages to using jtag? It just seems extra hassle with port pins sharing the jtag interface.

 

Perhaps on SAM chips, or should I just stick with SWD?

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It's easy to stop breaking the 10th commandment! Break the 8th instead. 

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jtag is easy to use if the port pins it uses are not part of the issue your trying to debug!

Try it, you'll like it!

 

Jim

 

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JTAG is always my first interface of choice. It's just so easy to use - it just works. All these others have you messing around with all kinds of mode switching or making sure reset pins are not loaded or whatever else. For JTAG you just connect the four pins and off you go. In fact for most things I wouldn't even bother asking the hardware to lay out ISP or whatever else as everything is achievable over JTAG anyway.

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PDI and UPDI seem to work very well on Xmega and Mega-0 series.

No special configuration.   They work out of the box.

 

SWD works very well on ARM devices.    As far as I know,  you can only debug one SWD target at a time.

 

JTAG uses more pins but you can access multiple targets in a daisy-chain.   (I have never done this)

 

I am struck by how effective debugWIRE is on a leg-constrained chip.

It is inherently slower than other interfaces.    Manageable with an ATMEL-ICE but the XMINI's mEDBG chip is glacial.

 

Yes.  JTAG uses more pins.    I disable JTAG to release the pins.   Then use SWD on ARM targets or PDI on Xmega.

You don't always need all the SWD pins.    But this gets into Cliff's "mode" whinge territory.

 

David.

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For us "language deficient" Americans, what is "whinge"?

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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I had assumed it was fairly universal in the English speaking world.

 

Wiktionary

 

Australians usually refer to us as Whingeing Poms.

 

I suspect that our European neighbours have developed a similar expression for our current Brexit phenomenon.

 

I was surprised to see that it is not used by U.S.

Perhaps Canadians use it.

 

David.

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Whinge is what 6 years old kids do in the back of a car after a 4 hour car journey leading to incessant "are we there yet?" 

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I think in the USA we use "whine" in a similar way, although Merriam-Webster tells me they are not variant spellings of the same word, but have separate roots.

 

I recently moved to JTAG, after a lot of confusion on my part, because the ATmega1284P I am using does not have debugWire, which I am used to.  I like JTAG.  As Cliff and other say, it just works, for programming and debugging.  I did have to get some .050 perfboard to wire up for the 10 pin header on the Atmel ICE.  These worked great from:   https://blackmesalabs.wordpress.com/2017/12/03/bml-50mil-0-050-proto-boards-for-rapid-surface-mount-prototyping/ .  0.050 spacing on the inside, 0.10 spacing on the outside.

 

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"Dare to be naïve." - Buckminster Fuller