Viewing Issue Advanced Details
ID Category [?] Severity [?] Reproducibility Date Submitted Last Update
06772 Gameplay Major Always Nov 22, 2017, 20:31 Nov 23, 2017, 14:42
Tester MrGW View Status Public Platform MAME (Self-compiled)
Assigned To hap Resolution Fixed OS Linux (64-bit)
Status [?] Resolved Driver dragon.cpp
Version 0.191 Fixed in Version 0.192 Build 64-bit
Summary MESS-specific 06772: Dragon machines run too fast!
Description Best guess is this in dragon.cpp:

static MACHINE_CONFIG_START( dragon_base )

        // basic machine hardware
        MCFG_CPU_ADD("maincpu", M6809E, DERIVED_CLOCK(1, 1))

My MAME-fu is poor, but looks like CPU clock being derived from PAL colour
subcarrier frequency. Of course, CPU rate should be a subdivision of
SAM rate depending on its settings as per CoCo.
Steps To Reproduce Reproduce by just running anything on a dragon32 or dragon64.
Additional Information Ciaran Anscomb (XRoar author) discovered this issue and provided his initial analysis of what he believes is causing the issue.
Flags Verified with Original
Regression Version
Affected Sets / Systems
Attached Files
There are no relationship linked to this issue.
User avatar
Nov 22, 2017, 22:20
It looks like the motherboard has 2 XTALs: 4.443619MHz(PAL subcarrier), and 14.2180MHz(main).
Pippin(Dragon prototype) and the 1st version of Dragon 32 Mark I have a 14.31818MHz main XTAL instead. MAME doesn't emulate these machines(yet?). 2nd version of Dragon 32 Mark I, Mark II, and every other Dragon after that, has a 14.2180MHz main XTAL.

photos here:
User avatar
Nov 22, 2017, 22:34
edited on: Nov 22, 2017, 22:35
It's fixed now.
Note: don't be misled by MAME's reported CPU speed of 3.55MHz. The M6809E has an internal /4 divider, making the practical CPU speed 0.89MHz.
User avatar
Nov 23, 2017, 14:42
Thanks for fixing this one too, hap!!