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I solved the problem - it is CONF_DONE, pin 138. I used it as an option pin for debugging and when I strapped it to Gnd, the MAX10 chip stopped working. Once the jumper is removed, everything is OK.
In the Quartus dialog Assigments->Device->Device andPinsOptions->General there is a check box "Enable nCONFIG, nSTATUS, and CONF_DONE pins". I understood that by un-checking the check box I will be able to use any of these pins as regular inputs. It turns out that tying CONF_DONE to Gnd prevents the MAX10 device from entering user mode regardless of the state of the check box!
The description of the check box in the dialog reads:
"Enables major configuration pins, nCONFIG, nSTATUS, and CONF_DONE pin in user mode. If this option is turned off, the nCONFIG, nSTATUS, and CONF_DONE pins are disabled when the device operates in user mode and is available as a user I/O pin."
I think there is a bit of ambiguity here because if the CONF_DONE intended to be used as an input and that input is low (tied to Gnd) the part will not enter user mode. I feel it would help users if Altera clarify that.
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Vgelman,
The pins are dual purpose and can be used in user mode. But you have to account for what happens before the device can enter user mode: configuration mode. The configuration pins(nconfig, nstatus and conf_done) need to be pulled high for successful configuration. A high CONF_DONE usually signify a successful configuration. The FPGA can't tell if the configuration is successful if the CONF_DONE does not go high. In your case the FPGA will always think that it is still in configuration mode since CONF_DONE is tied to ground. If you want CONF_DONE to be low, you can set it to GPIO low, in which the changes will take effect once you enter user mode. Cheers :)
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