Re: [hatari-users] Floppy in Falcon mode

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

On 25/12/2011 22:50, Vincent Rivière wrote:

> I measure the time taken for the Restore command by using Hatari's VBL
> traces between "fdc type I restore" and "fdc complete command". On
> Falcon it is (156 - 12) = 144 VBLs which means 2.4 seconds at 60 Hz.
> According to fdc.c, it should be 1.2 second (1.2 second for motor on and
> ~0 second for Restore from track 0).
>
> So it seems that the FDC delays are twice as expected in Falcon mode.
> This is enough to explain all my trouble.

Hello,

I barely use the Falcon mode, so I never noticed this.

In fact, the Falcon Ajax FDC uses a 16 MHz clock, while other ST models 
use a 8 MHz, and a stated in FDC_DelayToCpuCycles, FDC_Freq is expected 
to be the same as CPU_Freq (ie 8 MHz) for correct timings calculation.

So, on Falcon converting an FDC delay from microsec to cpu cycles 
returned twice the expected value. This is now corrected, I added a 
special case for Falcon to correct the cpu cycles.

All your delays should now be the same as on STF.

example from tos 4.04 booting in falcon mode :

fdc write 8604 data=0x0 VBL=133 video_cyc=878 366@1 pc=e045d2
fdc write 8604 command=0x0 VBL=133 video_cyc=878 366@1 pc=e045d2
fdc type I restore drive=0 current_track=0x0 VBL=133 video_cyc=878 366@1 
pc=e045d2
fdc start motor VBL=133 video_cyc=878 366@1 pc=e045d2
fdc complete command VBL=193 video_cyc=11854 78@23 pc=e04524


Thanks for noticing this.

Nicolas