A3BU Xplained board annoyances

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It seems that to activate the installed DFU bootloader, a power-on reset is required.  A software generated reset or external reset won't do.  I have to yank the USB cable out of the PC and plug it back in while holding down switch 0.  What if I only had one hand?  I would have to yank out the cable and replace it with my teeth, or press switch 0 with my nose.  smiley

 

Speaking of external reset, there is no reset push button on the board.  Am I the only one who wants such a thing on a development board?

 

The JTAG 10 pin header can be used for PDI, but the PDI data signal is connected to the JTAG TDO pin.  That means I either have to cut a "strap" on the board or change the JTAG enable fuse bit in order to use PDI.  I wonder why the otherwise unused pin 8 of the JTAG header wasn't used for this, like was done on the 128A1 Xplain board.

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I discovered the installed DFU bootloader will be entered following an external reset, unless the reset status register shows that a software reset has also occurred since the last power on. 

 

I guess that could make sense.  Apparently the bootloader does not want to run if it gets control from a software reset.  I guess it will run only if it gets control from an external reset.  The software cannot tell which reset occurred last if there are multiple resets shown in the reset status register, so if both the external and software resets have occurred, it jumps to the app. 

 

To give some flexibility to the programmer, the software can clear any bits in the reset status register.  For instance if you clear all the bits, then after the next reset there will be only one bit set in the register, and the source will be known.

 

I guess what's true of the software reset is also true of other reset sources, but I haven't tested them.

 

So now I can enter the bootloader with an external reset, provided I've added a reset button to the board, which I've done. 

Last Edited: Mon. Dec 29, 2014 - 01:13 PM