summaryrefslogtreecommitdiffstatshomepage
diff options
context:
space:
mode:
author MetalliC <0vetal0@gmail.com>2019-07-30 01:03:26 +0300
committer MetalliC <0vetal0@gmail.com>2019-07-30 01:03:26 +0300
commit08421800ef9a13e99c956fe6eaeb34389ee4c1a9 (patch)
tree7b4b34ec2d209488fb5809cbb7ebe0f1d920ef1d
parent2529c28832f10e623d9e988ce1269f3579df6837 (diff)
Atomiswave checksum and keys notes [brizzo, MetalliC]
-rw-r--r--src/mame/machine/awboard.cpp10
1 files changed, 7 insertions, 3 deletions
diff --git a/src/mame/machine/awboard.cpp b/src/mame/machine/awboard.cpp
index ee6fb7d5b73..843e3a52724 100644
--- a/src/mame/machine/awboard.cpp
+++ b/src/mame/machine/awboard.cpp
@@ -25,9 +25,10 @@ Atomiswave ROM board specs from Cah4e3 @ http://cah4e3.wordpress.com/2009/07/26/
Both low and high words of 32-bit offset from start of EPR-ROM area. Used for
reading header and program code data, cannot be used for reading MPR-ROMs data.
- During program code DMA transfer Romeo MCU perform data checksuming (decrypted data, in 8bit units),
- result must match some CPLD / encryption key-specific value, otherwise MPR-ROM access
- described below will not work correctly.
+ During program code DMA transfer Romeo ASIC perform data checksum - 8bit sum of
+ decrypted data bytes with swapped 4bit nibbles. Result must be equal to 8bit
+ decryption key provided by cartridge CPLD, otherwise MPR-ROM access described
+ below will not work.
Game header (first 256 bytes of ROM) is not checksum protected.
AW_MPR_RECORD_INDEX Register addres: 0x5f700c
@@ -189,6 +190,9 @@ These subfields could be differing from the "real" ones in the following ways:
- Of course, the way in which we are mixing 3 subfields in one only key is arbitrary too.
The keys are stored as 32-bits big-endian values in a file.
+
+Real keys provided by cartridge CPLD is only 8bit, bits 4-5 is sbox table index, bits 6-7 is permutation table index.
+But it is not clear how 16-bit XOR value derived from 8bit key.
*/