diff options
Diffstat (limited to 'src/mame/drivers/gng.cpp')
-rw-r--r-- | src/mame/drivers/gng.cpp | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/src/mame/drivers/gng.cpp b/src/mame/drivers/gng.cpp index 7c013a48f85..01065ca6695 100644 --- a/src/mame/drivers/gng.cpp +++ b/src/mame/drivers/gng.cpp @@ -20,6 +20,14 @@ Notes: - Increased "gfx3" to address 0x400 sprites, to avoid Ghosts'n Goblins from drawing a bad sprite. (18/08/2005 Pierpaolo Prazzoli) + Notes by Jose Tejada (jotego) + +There is no watchdog in GnG, as previously stated in the MAME driver. +Instead, there is a DMA circuit that copies object data from the CPU RAM to a buffer +this also slows down the CPU as it is halted during that time. +The DMA is triggered when a certain memory location is addressed. That location was +thought to be a watchdog before. + ***************************************************************************/ #include "emu.h" @@ -71,7 +79,7 @@ void gng_state::gng_map(address_map &map) map(0x3a00, 0x3a00).w("soundlatch", FUNC(generic_latch_8_device::write)); map(0x3b08, 0x3b09).w(FUNC(gng_state::gng_bgscrollx_w)); map(0x3b0a, 0x3b0b).w(FUNC(gng_state::gng_bgscrolly_w)); - map(0x3c00, 0x3c00).noprw(); /* watchdog? */ + // 0x3c00 is the DMA trigger. Not emulated. map(0x3d00, 0x3d07).w("mainlatch", FUNC(ls259_device::write_d0)); map(0x3e00, 0x3e00).w(FUNC(gng_state::gng_bankswitch_w)); map(0x4000, 0x5fff).bankr("bank1"); |