Troubles while configuring Flex 10K20TC144 in PS mode from microcontroller

[GTT95]

Hello,

I am trying to configure Flex10K20 from a PIC MCU using 1 bit passive serial mode.

The .rbf configuration file I get from quartus is exactly 28941 bytes in size. It is programmed into PIC's internal Flash and sent to FPGA upon each power on. After sending all 28941 bytes, starting each byte with LSB, I don't see CONF_DONE go high. 

However, while monitoring nSTATUS it goes low for 2µs, after 58ms following the start of sending data serially into the FPGA. The whole process of sending all 28941 bytes lasts arround 200ms.

The fact that nSTATUS goes low for 2µs does it signify an error within the configuration process? Is nSTATUS not expected to stay low for the whole remaining configuration process?

On what criteria does the device determine the configuration went wrong? Is the data checked on the fly? Shall all 28941 bytes be sent to have CONF_DONE go high? 

What could cause nSTATUS go low after 58ms, a wrong byte in the configuration file at this point?

In the design INIT_DONE is left unconnected (as there is no need in PS mode to poll for it).

Thanks a lot for helping me.