Re: [hatari-devel] hatari tt scc emulation

[Eero Tamminen <oak@xxxxxxxxxxxxxx>]

Hi,

On 07/17/2017 08:07 PM, Christian Zietz wrote:
> Eero Tamminen schrieb:
>
> > On 07/17/2017 09:43 AM, Christian Zietz wrote:
> > > I'm quite confident that -- if required -- I could provide a test case
> > > that does not need MiNT and that will crash at the same instruction
> > > inside TOS 3.06.
> >
> > That would be useful!
>
> Please find attached the test case, in source form as well as compiled
> with Pure C. This little programs tests that Bconmap and the TT SCC are
> available, then it reads the current baud rate and sets it again -- all
> using XBIOS functions, not direct HW access.

Thanks!

It seems to need at least TOS v2.  It doesn't crash on ST/STE/Falcon,
and crashes on TT, unless Hatari is patched.  I.e. it demonstrates
the issue fine. :-)


Btw. What you've compiled it with?  It has FPU check bus error
at startup.


> Under Hatari with TOS 3.06
> and TT emulation, this crashes in TOS code while accessing the SCC
> Channel B control register at $FFFF8C85:
>
> Bus error exception at 0xe0312a!
> $00e0312a : 14bc 000c                          move.b    #$c,(a2)
>
> ... where A2 is $FFFF8C85.
>
> I don't think the application (be it MiNT or be it my testcase) can be
> faulted for using XBIOS functions to access a serial port that TOS
> claims is available.
>
> > Michael, attached is (untested) patch to disable SCC write bus errors.
>
> I'm afraid there's something wrong with it. TOS 3.06 crashes during
> startup. It seems like access to the SCC DMA control ($FFFF8C14) also
> needs to be intercepted. When I add...
>
> { 0xff8c14, SIZE_WORD, IoMem_VoidRead, IoMem_WriteWithoutInterception },
>         /* SCC DMA */
>
> ... to ioMemTabTT.c, the sample FreeMiNT installation provided to me by
> Michael boots without crashing.

So it seems.  Attached is more complete version of the patch others
can try (has both changes + comments).


	- Eero

diff -r 5cfcf542f273 src/ioMemTabTT.c
--- a/src/ioMemTabTT.c	Mon Jul 17 11:41:33 2017 +0200
+++ b/src/ioMemTabTT.c	Thu Jul 20 00:38:59 2017 +0300
@@ -133,7 +133,15 @@
 
 	/* Note: The TT does not have a blitter (0xff8a00 - 0xff8a3e) */
 
-	//{ 0xff8c80, 8, IoMem_VoidRead, IoMem_WriteWithoutInterception },         /* SCC */
+	/* TODO: Current TT emulation is missing SCC emulation (+ required MFP updates).
+	 *
+	 * Although these registers aren't implemented, it's better to disable them,
+	 * otherwise TOS v3 crashes any program trying to use Rsconf(), such as MiNT
+	 * which startup code iterates through serial devices.
+	 */
+	// { 0xff8c00, 14, IoMem_VoidRead, IoMem_WriteWithoutInterception },                       /* SCC DMA */
+	{ 0xff8c14, SIZE_WORD, IoMem_VoidRead, IoMem_WriteWithoutInterception },                /* SCC DMA control */
+	{ 0xff8c80, 8, IoMem_VoidRead, IoMem_WriteWithoutInterception },                        /* SCC ports */
 
 	{ 0xff8e01, 1, IoMem_ReadWithoutInterception, IoMem_WriteWithoutInterception },         /* SCU system interrupt mask */
 	{ 0xff8e03, 1, IoMem_ReadWithoutInterception, IoMem_WriteWithoutInterception },         /* SCU system interrupt state */