Minimig Discussion Forum

Hello,

I am working on porting the minimig to the Cyclone III FPGA.
So far, everything looks good. The only issue is the floppy drive emulation .
I cannot get the "hand" screen under KS 1.3 or the disk animation under KS 2.0.
With KS 2.0, DF0 is recognized in the boot menu.

Any ideas ?

BTW, I improve sligntly the kickstart loading speed by using double buffering in the bootloader : I DMA 16KB of data in buffer #1 while copying 16KB of data from buffer #2 into KS area and vice-versa. DMA is constantly on (213KB/s with DMA floppy acceleration).

Regards,

Frederic

As far as I can tell, the CIA interrupts must work normal to get any initial kickstart picture.

Perhaps also without a working floppy controller, some necessary signal is missing and prevent kickstart from finding any floppy drive.

Hello,

Thanks for the hint.
I totally replaced floppy.v and have a custom floppy controller : it does not use a SPI link but a parallel link.
I do not have a ARM or PIC but a NIOS II CPU inside the same FPGA.

I am halfway through disassembling the trackdisk.device. I can see already that the disk.resource correctly auto-detects the drives.
I am going to look at the CIA interrupts but it looks like they work since the multi-tasking runs correctly (Exec uses the timer.device for the multi-tasking time-slice).

Regards,

Frederic

You may try to set some floppy signal to permanent value, just to figgure out a possible missing signal handling.

Try for example in Floppy.v:
assign _ready = 0; // drive is always ready
assign _sel[3:0] = 4'b1110; // should select DF0 only

and comment out the other assignments.
Sure this will not make the floppy drive work, but perhaps the kickstart picture appear to have a clue where to search for.

Hello,

I found the issue : it was in the 8520.
With the current CIA8520.v, the ICR register is cleared as soon as the ICR is selected ("icrs" signal) and "wr" is deasserted.
On the normal Minimig implementation, the cpu bridge works around this problem.
I am using a implementation with a TG68 on a Cyclone III.
There is no cpu bridge and a different gary implementation.
I modified the CIA8520.v by using a falling edge detector on "rd" to clear ICR.
I would like to post the modification, how can I do that ?

Regards,

Frederic

Thanks for you time finding and fixing this matter!

I think here is the right place to post the new code.
Perhaps with an adapted posting subject, to make it search engine compatibble