Locked/unlock AVR on the USBasp doesn't matter. You can simply erase the chip to remove the lock, set the fuses again, then burn/upload the image you want.
it definitely matters if the unit was locked and stops working with other firmware and we were not able to restore original because we couldnt read it. fortunately this happened with very few models.
True that having a locked AVR on the USBasp will prevent reading the original firmware
to save it away for the possibility of restoring it, but
from your previous comment:
you are lucky to find one unlocked but all mine came locked.
I was assuming you were referring to LOCK fuse bits and the inability to update
the AVR if the LOCK bits were set.
LOCK fuse bits being set doesn't prevent the AVR from being re-programmed
so a locked avr on a USBasp device won't matter with respect the ability to re-flash
a new/updated USBasp firmware image.
You could use a different programmer. Many like the newer USBtiny or the Dragon have logic levelers and will adjust
to the targets voltage level.
i own mkII, dragon, and a couple usbtiny. they all had issues and more problems in my applications than usbasp. then theres the fact that i can buy 20 usbasp for the cost of one dragon and 10 for the cost of a mkII. of course usbasp dont have jtag or dbw ability but neither do my chips so dragons pretty much sitting on a shelf.
I brought up the other devices as devices that could be used to update the firmware on the
the USBasp devices that you ship to your customers.
I wasn't intending that that be used as alternatives for programming devices for the customers.
personally id advise against reflashing unless there is good reason and its known to be safe.
I wouldn't go that far.
I'd say updating is actually a good thing as it removes a bothersome warning from avrdude
and also adds in functionality that can be required in some environments.
However, I'd also say don't just blindly flash an updated Fischl image into the device.
The key is to reflash an image that works with the target hardware.
So in order to be sure the image works with his hardware, the
USBasp device hardware design must be compared to the Fischl reference design.
The USBasp hardware is very simple. It is typically on dual sided PCBs so it is very easy
to follow all the traces and decide if it matches the Fischl hardware.
If it doesn't exactly match, the user can then decide if they wish
to tweak the firmware source code to match the wiring using on their PCB and rebuild it
or whether to not do the re-flash.