2021-06-22 13:05:09 +00:00
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EttinOS
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=======
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EttinOS is a minimalist 16-bit DOS-like hobbyist operating system for
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2021-06-24 15:34:41 +00:00
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the IBM Personal Computer and compatible machines. Its git repository
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can be found at https://ahti.space/git/crazyettin/EttinOS.
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2021-06-22 13:05:09 +00:00
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System requirements
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-------------------
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* An Intel 8086 or compatible CPU
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* BIOS, or UEFI in legacy mode
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* 64 KiB of RAM
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* A floppy disk drive
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Building
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--------
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Build dependencies:
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* A Unix-like operating system
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* coreutils
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* dosfstools
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* mtools
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* nasm
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2021-06-25 17:24:38 +00:00
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* rw (optional)
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Running make.sh will build EttinOS and create a bootable 360 KiB 5.25"
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floppy disk image named EttinOS.img. To get a 1.44 MB 3.5" one instead
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use the argument -1440. If you want to use another floppy disk format
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you will have to adjust the bootloader disk description tables and
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install the system manually. Hard disk drives are not supported.
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Input
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-----
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The EttinOS input system is inspired by typewriters. Typing a character
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overwrites the cursor location and the erase (=tab) key erases it. The
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space and backspace keys move the cursor.
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2021-06-25 17:24:38 +00:00
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Commands
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--------
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EttinOS commands consist of the case-insensitive command itself followed
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by a tail separated with a space. Extra spaces, be they leading,
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trailing, or between a command and its tail, are ignored. What the tail
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contains and how it should be formatted depends on the command. Tails on
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commands that do not use them are ignored. All commands except for
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changing the drive are stored as external programs, and you must be on
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the same drive as the program file to execute one. A command for a
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program does not include its filename extension.
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Commands included in EttinOS by default:
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* [A-D]:: Changes the drive.
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* ECHO: Echoes its tail.
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* HELLO: A hello world program.
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2021-06-22 13:05:09 +00:00
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Programming
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-----------
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EttinOS has a flat address space of 64 KiB. The data, stack, and
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extra segments are set at the beginning of the RAM and the system stack
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at the end of the address space. Programs are loaded at address 0x2000
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and SI is pointed at the command tail, a string ending in a null, when
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the program is executed. The stack is reset back to the end of the
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address space after a program has finished running.
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System calls:
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* Interrupt 0x20: Return to the shell.
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* Interrupt 0x21: Input and output:
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* AH = 0x0: Print a string ending in a null from SI.
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* AH = 0x1: Read a string ending in a null of at most AL
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characters to DI until a return.
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* AH = 0x2: Print a string ending in a null from SI followed by a
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CRLF.
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* AH = 0x3: Read a string ending in a null of at most AL
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characters to DI until a return and print a CRLF.
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* Interrupt 0x22: Disk operations:
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* AH = 0x0: Load a file named in SI as a string ending in a null
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to the offset BX and set AL to 0x0 if the load was
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succesfull and 0x1 if there was an error.
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* AH = 0x1: Save a file (under construction).
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