Commodore 64: Wildload loader

@DrWatson

Published in 

C64 tape formats

 · 18 May 2021

Can be found on...Andy Capp, Championship Sprint, Citadel, Crazy Coaster, Delta, Enduro Racer, Into the Eagles Nest, Joe Blade, Joe Blade 2, Quedex, Rampage, Super Hang-On, Tetris, Wonderboy...

Threshold = $1E0 (480) clock cycles (TAP byte = $3C).

 Bit 0 : $30 
 Bit 1 : $47 
 Endianess : LSbF 

 Pilot byte : $A0 (*256) 
 Sync : $0A down to $01  
 

After the sync sequence is a series of varying size sub-blocks, they are laid out end-to-end without gaps and each one is organised as follows...

• 2 bytes : End address (LSBF)
• 2 bytes : Data size (LSBF)
• 1 byte : Unknown
• n bytes : Data (enciphered. real byte = byte XOR with destination address low byte)
• 1 byte : Checkbyte

Notes:

• The data is loaded in from End to Start (decreasing RAM addresses + data is written out backwards).
• The checkbyte value is.. 0 XOR with all (deciphered) data bytes.
  
• The end address and data length of the final block will both be 0.
  
• The final block (end address and length are $0000) consists of 6 bytes (actually 47 pulses)
  

I treat this as a small secondary filetype called "Wildload Stop".

• 2 bytes : End address ($00,$00)
• 2 bytes : Data size ($00,$00)

then 2 bytes, the last one has only has 7 pulses and im not sure what they do yet.

After final block (Wildload STOP) is sometimes around 8 pulses, these are safe to remove.