sizecoding-tools

Motivation

I released an effect that under some circumstances did not work as expected, probably because it depends on the initial state of the memory when starting DosBox.

When talking about this with hannu, he mentioned him researching the different initial memory states in all the possible execution environments for DOS code (like Dosbox, Dosbox-stagging, Dosbox-x, FreeDos, ... in all their different versions and host OSes).

So I thought a tool for being able to look at the contents of the memory might be helpful.

hashmem (version 1.3)

Displays a map of hashes of the first 1MB of memory in chunks of 1kb blocks and all non zero blocks in a 64byte-detailed view. This is useful to compare the initial state of DOS environments.

Visuals

• Version of hashmem.
• Initial values of registers.
• You see 1MB of memory in tabular form.
  • Each of the 16 rows spans 64kb of memory.
  • Each line shows it starting segment address and then prints 64 hashes (1 char per hash) that each represent 1kb of memory.
  • If the 1kb block of memory is completely filled with zeros the hash shows '.' or ':', otherwise it shows one of 0-9, a-z or A-Z.
  • Most of memory is filled with zeros.
  • At the end of each line the last 4 bytes of the 64kb segment are shown plain.
  • Upper left corner shows the segment the code of hashmem.com is loaded to. So the hash of this 4kb patch (and the one a row below that, cause of the stack) is influenced by the code that is executed and does not necessarily stem from environmental differences.
• "Details" - show a detailed view of all 4kb patches, that did contain at least one non-zero byte.
  • the length of this view may vary
  • the layout of each line is the same as in the first overview part, only now one char does represent a 64 byte block and not a 1kb block

Observations in Dosbox

• Graphics memory at 0xA000 is completely filled with zeros.
• The first page (4kb) of textmode memory at 0xB800 is different every time, because the tool itself is actively writing on the screen.
• The other pages of textmode memory are all the same but not zero.
• In consecutive executions of this tool in the same environment only three of the 4kb patches change:
  • 0x0000: Does change by time (maybe timer at 0x46C). You can see a blinking pixel using showmem.com.
  • 0x0100: Does also change by time (no clue why). You can see several wildly blinking memory locations there (see showmem.com below). This 4kb page also contains the loaded programm, but as long as the version of code does not change it should not influence the hash of this page.
  • 0xB800: Screencontent is different every time, because of changes in 0x0000 and 0x0100 -> so hash changes.

Maps of common platforms

see Samples for known memory-hash-maps dosbox installations.

showmem (version 1.0)

Scrolls through all of 16x64k (= 1MB) of memory accessible by the combination of segment and offset register like [es:di].

Controls

ESC => You can pause and resume the scrolling by pressing ESC.

Possible future features

• scrolling by arrow keys and page-up and -down keys
• printing hashes for stripes of memory to make them comparable between different environments

Visuals

• every line shows 256 byte of memory

• the mode13h default palette is used (0 = black, 1 = blue, 2 = green, ...)

• those 256 byte are followed by a byte that shows the "line-number" modulo 256 as a colored pixel

• the rest of the line is filled with the color representing the number of the current 64k segment of memory

  • 0 = 0x0000:0000 - 0x0FFF:FFFF (black)
  • 1 = 0x1000:0000 - 0x1FFF:FFFF (blue)
  • 2 = 0x2000:0000 - 0x2FFF:FFFF (green)
  • 3 = 0x3000:0000 - 0x3FFF:FFFF (cyan)
  • 4 = 0x4000:0000 - 0x4FFF:FFFF (red)
  • 5 = 0x5000:0000 - 0x5FFF:FFFF (magenta)
  • 6 = 0x6000:0000 - 0x6FFF:FFFF (brown)
  • 7 = 0x7000:0000 - 0x7FFF:FFFF (light gray)
  • 8 = 0x8000:0000 - 0x8FFF:FFFF (dark gray)
  • 9 = 0x9000:0000 - 0x9FFF:FFFF (bright blue)
  • A = 0xA000:0000 - 0xAFFF:FFFF (bright green)
  • B = 0xB000:0000 - 0xBFFF:FFFF (brigth cyan)
  • C = 0xC000:0000 - 0xCFFF:FFFF (bright red)
  • D = 0xD000:0000 - 0xDFFF:FFFF (bright magenta)
  • E = 0xE000:0000 - 0xEFFF:FFFF (yellow)
  • F = 0xF000:0000 - 0xFFFF:FFFF (white)