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Unable to get Nios-II F going, Nios-II S works fine in same config. (DE2-115 + SDRAM)

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Hello All,
I have a DE2-115 running a Nios-II S(low) with the on board SDRAM (basic config, HELLO WORLD application). 50 Mhz clock, 3ns delay for the ram clock, no FPGA RAM used.
When I change to Nios-II-F(ast), using the same configuration I am unable to start the CPU (an exception is thrown at startup).
I wonder what can be the reason ?
What is a bit strange is that the OpenCore dialog box (Quartus Lite Edition 17.0) does not come up when I download. I know that the Slow CPU does not need the Open Core licence (as it seems), but I thought that the F version did.

If so, how can I convince Quartus to launch OpenCore upon download of my VHDL project ?
To be sure there are no hickups in Eclipse, I generate a new program based on the SOPC file generated by QSYS, so I do not use an updated BSP to start from when changing the CPU type. The old configuration cannot pollute the new one.

The exact error I get is that Nios throws an exception and ends up at Nios2_BREAK() (alt_instruction_exception_entry.c). This after I oblige eclipse to download by overruling the timpmestamp check that is not correct.) Since I generated a brand new file based on a newly generated Sopc file, this also seems very strange. Iam also very sure I download the correct version to my FPGA board. (tried it multiple times)

Backtracking on the stack, the exception seems to be generated in alt_get_fd.c, getting a descriptor for my Jtag Uart. Very strange because for the -S CPU this works properly ? The exact line is line 79 where alt_fd_list[i].dev is accessed.
for (i = 0; i < ALT_MAX_FD; i++)
{
if (!alt_fd_list[i].dev) <= this line
{
alt_fd_list[i].dev = dev;
if (i > alt_max_fd)
{
alt_max_fd = i;

}

rc = i;
goto alt_get_fd_exit;
}
Is there anybody who got the -F cpu working on an SDRAM config for the DE2-115 in a Quartus lite config?
Is anybody able to explain what I did wrong or forgot ?

Thanks for any advice,
Johi.


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