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slapstic: Some more information

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This commit is contained in:
Olivier Galibert 2020-12-18 16:28:43 +01:00
parent 1df245cb99
commit c54bde154f
1 changed files with 23 additions and 2 deletions
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25
src/mame/machine/slapstic.cpp
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@ -16,7 +16,8 @@
The slapstic was a security chip made by Atari, which was used for
bank switching and security in several coin-operated video games from
1984 through 1990.
1984 through 1990. It means "SLA Protection from Software Thievery IC",
where SLA is a Storage/Logic Array, an early form of gate array.
What is a SLOOP?
@ -171,10 +172,23 @@
independently. Later chips (111-118) provided a mechanism of adding
1, 2, or 3 to the number of the current bank.
One important detail is that some accesses must be done with CS=0,
while others don't care. CS=0 usually means the access is in the
slapstic banked region. Specifically:
- on 101 and 102, the 2nd alt access must be done outside of
the bank region
- on 103 to 108, the 1st alt access can be done anywhere
- on 110 to 118, the 1st and 3rd alt access can be done anywhere
These out-of-range accesses pose technical difficulties we're not fully
handling yet. Similarly, accesses that must be done in sequence get
broken by an out-of-range access.
Surprisingly, the slapstic appears to have used DRAM cells to store
the current bank. After 5 or 6 seconds without a clock, the chip
reverts to the default bank, with the chip reset (bank select
addresses are enabled). Typically, the slapstic region is accessed
addresses are enabled). Typically, the clock is connnected to the
cpu memory access line (AS on the 68000 for instance), accessing
often enough to avoid the problem.
For full details, see the MAME source code.
@ -260,6 +274,10 @@ static const struct slapstic_data slapstic101 =
{ 0x0080,0x0090,0x00a0,0x00b0 },/* bank select values */
/* alternate banking */
// Real values, to be worked on later
// { 0x1f00,0x1e00 }, /* 1st mask/value in sequence */
// { 0x1fff,0x1fff }, /* 2nd mask/value in sequence, *outside* of the range */
{ 0x1fff,0x1dfe }, /* 1st mask/value in sequence */
{ 0x1fff,0x1dff }, /* 2nd mask/value in sequence */
{ 0x1ffc,0x1b5c }, /* 3rd mask/value in sequence */
@ -287,6 +305,9 @@ static const struct slapstic_data slapstic103 =
{ 0x0040,0x0050,0x0060,0x0070 },/* bank select values */
/* alternate banking */
// Real values, to be worked on later
// { 0x3e00,0x3a00 }, /* 1st mask/value in sequence */
// { 0x3ffe,0x3ffe }, /* 2nd mask/value in sequence, *outside* of the range */
{ 0x007f,0x002d }, /* 1st mask/value in sequence */
{ 0x3fff,0x3d14 }, /* 2nd mask/value in sequence */
{ 0x3ffc,0x3d24 }, /* 3rd mask/value in sequence */