JTAG vs. PDI

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#1
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I'm evaluating Xmega for a new project and was wondering what the pros and cons of these two debug interfaces were (having only used JTAG and debugWire before). PDI looks superior due to its dedicated pins (I'm not planning on using boundary scan), but I'd prefer people's experiences over my reading of the datasheet. Thanks.

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PDI is good, as long a you don't need a cap on the reset line for EMC immunity. I prefer PDI over JTAG when I have the option.

Hans-Christian

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Any problem with using a jumper to switch the cap in and out, in case I want to update something in the field?

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lautman wrote:
... in case I want to update something in the field?
An alternative to PDI is to use a bootloader.
Ref.
1. Atmel AVR1605
2. XBoot

"Dare to be naïve." - Buckminster Fuller

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PDI always works a bit faster than jtag for me. I'm pretty sure jtag just interfaces to the PDI controller anyway so there's really no advantage unless your debugger doesn't support PDI such as the dragon.

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Quote:
Any problem with using a jumper to switch the cap in and out, in case I want to update something in the field?

That's fine.

JC

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I'm currently working on a project that uses debugWire which I've found to be problematic (usually works, but I occasionally have to use an AVRISP to put things right). Has everyone found PDI to be reliable (plug-and-play)?

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I've not had any chip problems with PDI.
AVRISPmkII and STK600 both work reliably with the PDI interface.
I've had some issues using the Dragon for Xmega programming with the PDI interface, others have reported that it works for them.

JC

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Quote:

I'm currently working on a project that uses debugWire which I've found to be problematic (usually works, but I occasionally have to use an AVRISP to put things right). Has everyone found PDI to be reliable (plug-and-play)?

But you don't get a choice. A chip that has debugWire has no alternative. It's only some Xmega that have a choice between PDI and JTAG.

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Only problem with PDI is if you set the SUT to 64ms - then it can be a problem (sometimes).