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author Jose Tejada <jotego@gmail.com>2019-09-04 15:47:37 +0200
committer Jose Tejada <jotego@gmail.com>2019-09-04 15:47:37 +0200
commitda027a54976d7b8ef7782576998094f889441009 (patch)
treeaa069afeeabd416ae91b476c271e995160a6618f
parent80171a45ce42e98e7d6f45b592d9cda01d98b3d9 (diff)
Fixed main CPU frequency for Commando.
Removed watchdog from GnG
-rw-r--r--src/mame/drivers/commando.cpp17
-rw-r--r--src/mame/drivers/gng.cpp10
2 files changed, 24 insertions, 3 deletions
diff --git a/src/mame/drivers/commando.cpp b/src/mame/drivers/commando.cpp
index 0c93904e620..8d9f58404ec 100644
--- a/src/mame/drivers/commando.cpp
+++ b/src/mame/drivers/commando.cpp
@@ -44,6 +44,16 @@ Note : there is an ingame typo bug that doesn't display the bonus life values
***************************************************************************/
+// Notes by Jose Tejada (jotego):
+// The main CPU frequency is 3 MHz, after a two-stage FF clock divider.
+// The CPU clock is gated by bus arbitrion logic. The CPU clock is halted until
+// video hardware has an opening in memory access, then the CPU is allowed to
+// access common memory. This slows down the CPU but doesn't alter its basic 3MHz frequency.
+//
+// There is also 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.
+
+
#include "emu.h"
#include "includes/commando.h"
@@ -66,6 +76,7 @@ void commando_state::commando_map(address_map &map)
map(0xc004, 0xc004).portr("DSW2");
map(0xc800, 0xc800).w("soundlatch", FUNC(generic_latch_8_device::write));
map(0xc804, 0xc804).w(FUNC(commando_state::commando_c804_w));
+ // 0xc806 triggers the DMA (not emulated)
map(0xc808, 0xc809).w(FUNC(commando_state::commando_scrollx_w));
map(0xc80a, 0xc80b).w(FUNC(commando_state::commando_scrolly_w));
map(0xd000, 0xd3ff).ram().w(FUNC(commando_state::commando_videoram2_w)).share("videoram2");
@@ -225,7 +236,9 @@ GFXDECODE_END
#define XTAL 12000000
#define PHI_B XTAL/2/2
-#define PHI_MAIN 4000000 // ??? too complicated to trace from schematics
+#define PHI_MAIN XTAL/2/2 // As seen in the schematics:
+// the signal goes into a bus arbitrion logic that doesn't affect its frequency
+// although the CPU gets slowed down when accessing char/background memories
/* Interrupt Generator */
@@ -255,7 +268,7 @@ void commando_state::machine_reset()
void commando_state::commando(machine_config &config)
{
/* basic machine hardware */
- Z80(config, m_maincpu, PHI_MAIN); // ???
+ Z80(config, m_maincpu, PHI_MAIN); // 3 MHz
m_maincpu->set_addrmap(AS_PROGRAM, &commando_state::commando_map);
m_maincpu->set_addrmap(AS_OPCODES, &commando_state::decrypted_opcodes_map);
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");