Hi Christian & Nicolas,
On 14.6.2024 18.51, Christian Zietz wrote:
With some help from Eero (thank you!) I now have a kernel that I can
load on my real TT.
I can confirm:
1.) The unmodified kernel is indeed broken: It hangs in an infinite loop
"unexpected interrupt from 112" due to the active but unhandled VBL IRQ.
This should be reported to m68k linux.
2.) When I patch the kernel (with Ghidra and a hex editor) to write 0x00
to the SCU sys_mask register, it boots, only panicking in the end (as
expected) because I did not provide a root FS in my test.
Thanks for testing!
I was thinking of following "Atari SCU support broken" mail to m68k
Linux mailing list:
-------------------------------------------------
During the development of Atari TT / MegaSTe SCU support for Hatari
emulator, it was noticed that m68k Linux does not properly initialize
SCU registers / IRQ handlers on boot.
Currently Linux freezes at boot and spews "unexpected interrupt"
messages constantly on TT.
Nicolas Pomarède and Christian Zietz investigated:
* Issue to be due to VBL IRQ handler removal [1]
* boot to succeed if either 0x00 is written to the SCU sys_mask, or
handler is provided for VEC_INT4 [2] when SCU is used
Christian has verified the issue and its workaround on real Atari TT.
[1]
https://github.com/torvalds/linux/commit/1fa0b29f3a43f9dd8080d24cd16790b15ef963f5
[2]
https://git.tuxfamily.org/hatari/hatari.git/tree/tools/linux/0004-WA-avoid-unexpected-SCU-interrupts.patch
-------------------------------------------------
Does that sounds OK?