Re: [hatari-users] Floppy in Falcon mode

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Le 28/12/2011 03:09, Roger Burrows a écrit :
On 28 Dec 2011 at 0:30, Thomas Huth wrote:

So it seems that the FDC delays are twice as expected in Falcon
mode. This is enough to explain all my trouble.

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

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.

Great that this problem is fixed. But what about TT mode? Didn't the TT
have an Ajax chip, too? If yes, which frequency did it use?

I think early TTs had a WD1772 (max 8MHz, only good for DD) and later TTs had
an Ajax chip.  I have some documentation (the TT MCU RevB Functional
Description) that says that 0xff860e controls the frequency of the input clock
to the Ajax/1772 (either 8MHz or 16Mhz).  I assume that TOS 3.06 sets the
frequency, probably based on the DIP switch setting, but I've never checked

If anyone needs a copy of that MCU doc, let me know and I'll email it (I think
I got it from the Atari documentation site).

Roger Burrows

Yes, I also think that some TT models had a 8 MHz WD1772 (at least that's what is schown in the motherboard schematics I have), then it is said that Atari later replaced the WD1772 (even in STE) with the Ajax version at 8 or 16 mHz.

In the case of fdc.c, what's important for the correct delays is that we have a behaviour matching the description in clocks_timings.c


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