Mikro-Gen Loader
================
Info by Netraider (netraider@mail.pt)
Mikro-Gen Loader v1
These are amongst the first games released for the C64 and as such the loader is quite primitive. It doesn't even use CIAs for pulse timing.
Used by Pyjamarama (1984), Auto Mania (1985)
Mikro-Gen Loader v2 (aka Hyperload / Load'n Go)
Games using this loader include : Everyone's a Wally (1985),
Herbert's Dummy Run (1985), Witch's Cauldron (1985), Battle of the Planets
(1986), Frost Byte (1986), Equinox (1986).
Description:
Short pulse = $38
Long pulse = $66
Bit 0 = Short
Bit 1 = Long
Threshold = 512 clock cycles
Pilot (v1)= 256 pulses longer than 1441 cycles, followed by any number of
pulses between 884 and 1924 cycles (typically, 1024 pulses between 1441 and
1924 cycles)
Pilot (v2)= Bit 1 (at least*256) (exactly 2048 from TAPs)
Sync (v1)= one pulse shorter than 884 cycles
Sync (v2)= Bit 0
Endianess : LSbF
Checksum : Yes, last byte contains complement to zero of all added bytes (that
is, sum of all data bytes+checksum = 0 modulo 256).
The start and end addresses of a block are not in the block itself. Instead,
they are in the loader's code. In v1, there is a single block following the
loader. To get the start address, one has to find the following string in the
loader:
'a9 xxL 85 fd a9 xxH 85 fe ad 0e dc 29 fe 8d 0e dc'
xxL, xxH - start address (low/high)
To get the end address, one has to find the following string in the
loader:
'e6 fe a5 fe c9 yy d0'
The end address is yy*256-1.
In v2, here are 2 blocks after the loader, one for the loading screen and another for the main game.
The common way to indentify start and end address is searching the 2 occurrences of the following string in the loader, one for each block:
'a9 xxL 85 fd a9 xxH 85 fe a9 yyL 85 f8 a9 yyH 85 f9 ad 0e'
xxL, xxH - start address (low/high)
yyL, yyH - end address+1 (low/high)
At the end of each block there's a checksum byte.
After loading a block the checksum verification routine is called, that adds all bytes including the checksum byte containing the complement to zero of all added bytes.
If, during a load, a pulse's duration exceeds 1024 clock cycles, a load error condition immediately occurs.
(
geocities.com/siliconvalley/platform/8224) (
geocities.com/siliconvalley/platform) (
geocities.com/siliconvalley)