what is “SPIEN”, please？

[xiaoquanaa]

HI, big brother,i am sutdying to diy my first keybord with at90usb1286. i just don't know what this word "SPIEN"(like some words for short) means. could you let me (a green hand) know？

[digitalrane]

Hey, SPIEN is the fuse which enables SPI (SPI ENable) - if you don't set the SPIEN fuse, then SPI will be disabled, and because ISP requires SPI, then ISP programming won't work. Hope that helps!

[xiaoquanaa]

thanks for your reply! but i still have some trouble.
before i saw your project here, i customed a tiny pcb refering to the teensy++2.0 schematic
. and i bought a teensy+2.0 board and a blank chip of at90usb1286 , thus i have two chip of at90usb1286 ,i call the one on the board "teensy chip" , and another one "blank chip" . when i received my pcb board(5 pieces of sample) from the factory , i unsoldered the teensy chip away from the teensy board , and sodered the two chip on my customed pcb board . after that i linked the two soldered pcb to my pc with a usb-isp programer , and then comes the problem . the board with the teensy chip could be readed by PROGISP , but the blank chip can not be readed . and the teensy chip's fuse is like this

for the blank chip can not be readed , there is no fuse to be read out . i have checked and checked again the link of the isp , and the soldering of the blank chip board , but still failed to get the blank chip to be readed. i dont know why this could happen . here is some of my guesses:

1. the schematic of teensy could not be used to read a blank chip .as we konw there is a little difference between the schematic of teensy++2.0 and your ec0board sch(the PE2/HWB pin ,the ref pin , and the capacity near the Crystal and some vcc / gnd pins ).
2. the blank chip is fake or is a bad chip .
   can you give me some ideas to this problem , big brother?
   i have designed a new pcb according to your sch , but it is still one the way from the factory to me .

still another question : if i can read the blank chip on the new board and set the fuse you recommended , which bootloader should i burn into the blank chip , arduino bootloader or atmel one or any others ?

[digitalrane]

It is possible that the blank chip has fuses set to require an external oscillator or crystal, and it won't respond to programming if it does not have a clock. You may be able to connect a clock to it and get it to program, or if the clock is set incorrectly, sometimes you can slow down the SPI clock speed (using avrdude, this is the -B parameter) and get it working well enough to update the fuses for the correct clock speed.

If SPIEN is not enabled, and the clock cannot be recovered, your only other option would be high voltage programming mode, which requires a specific programmer such as the AVR Dragon.

If you can fix the fuses, I would use the bootloader that ships with QMK - (qmk-dfu) but you can also flash the atmel-dfu bootloader. QMK DFU is a fork of LUFA DFU, and is improved but still an open source alternative to atmel-dfu.

[xiaoquanaa]

thanks again , you helped me lot .
if i want to burn firmware to the chip through usb line instead of isp , which bootloader should i use ? the teensy board can do this , but the teensy bootloader is not open source .

[digitalrane]

QMK or LUFA both support DFU - which allows updating via USB, and are open source and actively developed - the atmel-dfu loader also supports DFU which allows updating via USB, but the QMK and LUFA loaders typically have more features.

[xiaoquanaa]

i have tryed to rescue my at90usb1286 by link a extra crystal XTAL2 from the teensy board to it's XTAL1 , but still failed to wake it up , so i gave it up , and bought a new at90usb646 by a more official access , and it can be read correctly .then i try to replace the original bootloader with the lufa and i find this
page ,https://mtm.cba.mit.edu/ppatil/FabFTDI/-/tree/004d53a7d167d78982bb65bbd1df22eacbcb978b/dev/lufa-LUFA-170418
and download the zip file , unziped it , but i don't know how to make the correct dfu bootloader for my new chip at90usb646 , cause i am not a programer . how should i edit the make file to make a bootloader for at90usb646 but not for any others .
i saw this document

but i don't know how and where to use this format .
if , when i burn the lufa bootloader to the chip correctly , how should i burn the keyboard firmware to it via usb , through which tool (qmk toolbox ?).

[digitalrane]

Once you burn a DFU bootloader, you typically reset the processor, and then use a generic tool like dfu-programmer to program it.

For compiling the bootloader, I suggest you see if you can find a pre-compiled bootloader image for your microcontroller. The avrfreaks.net forum would be a good place to ask, if anyone has experience with this specific MCU.