The Hummer (NTSC) ROM disected

More information can be found on the pages by Daniel Kahlin, see his page.

Directory Format

The directory is located at $010000-$013fff.

Each entry is 32 bytes long:

$00-$17 Filename max 24 bytes, padded with $00

$18-$1a Location of the file in flash (code/len/offset data).

$1b-$1d Load address of file in RAM.

$1e-$1f Offset of raw file data relative to location of the file in flash ($18-$1a).

Directory scanning stops when the first byte of the entry is $00.

Note that the directory presented when doing LOAD“$” is just a file named “$”, not the actual directory.

File Format

The files are compressed using a simple equal-sequence compression algorithm.

If differs from the DTV2 flash format a bit as raw data is stored at the end of the compressed stream instead of being interleaved with control data.

• Every chunk of data starts with a code byte.
• If code is $01-$7f, that number of bytes have to be read from the current raw offset.
• If code is $80-$ff, then len=code & $7f, and a second byte (offset) follows
  • this copies len bytes of data from the current destination-$0100+offset.
• If code is $00, then we are done.

Example

“HELLO” loaded to $0801:

$010018  00 00 10 01 08 00 02 00
         ^^^^^^^^                location of file in flash ($100000)
                  ^^^^^^^^       load address ($000801)
                           ^^^^^ raw data at $10000+$02=$010002
$100000  05 00 08 05 0C 0C 0F
         ^^^^^                   read five raw bytes, then exit
               ^^^^^^^^^^^^^^    five raw bytes