knekt

the kernel

knekt is the kernel core. most of what the kernel does lives in the named parts around it, and knekt is the piece that wires them together.

boot

GRUB boots the kernel through Multiboot into a short piece of hand-written assembly, which sets up just enough of the machine to call knekt's main. main wakes the machine a piece at a time, the serial port, the framebuffer (punkt), the keyboard, memory (jenna), the interrupt table and the timer. then it tiles the screen into windows (kakel), starts a shell in each (skalman) along with the scheduler (chrone), and brings up the filesystem (jakel).

when things go wrong

a fault in a ring-3 program ends that program and nothing else. a fault in the kernel prints the vector, the error code, the faulting address and the instruction pointer over serial and halts. a fixed capacity in the kernel that fills up says so on the serial port rather than dropping work without a word.

ring 3

programs are static elf64 executables, usually read from jakel. each runs in ring 3 with page tables, a kernel stack and a heap of its own, and talks to the kernel through the syscall instruction. in coff's --elf mode a program reaches them through builtins such as win_info() and readfile().

system calls

num	name	args	returns
0	`SYS_EXIT`	none	does not return
1	`SYS_DEBUG_PRINT`	str	none, the text goes to the program's window
2	`SYS_WIN_INFO`	none	`width * 65536 + height`
3	`SYS_FILL`	x, y, w, h, color	none
4	`SYS_KEY_POLL`	none	`make_code * 2 + is_break` or -1
5	`SYS_BLIT`	buf, x, y, w, h	none
6	`SYS_ALLOC`	size	address of zeroed memory, or 0 if exhausted
7	`SYS_TICKS`	none	the kernel's monotonic ~100hz pit tick count
8	`SYS_READFILE`	name, buf, max	bytes read, or the size when `buf` is 0, or -1
9	`SYS_PRESENT`	buf	0, or -1 with no window
10	`SYS_WIN_MAX`	none	`width * 65536 + height`
11	`SYS_MOUSE_POLL`	none	`(x * 1024 + y) * 8 + buttons`, window-relative, or -1 when the pointer is not over the window
12	`SYS_GLYPH`	ch, buf	`cell width * 65536 + cell height`, and the glyph's rows written to `buf`
13	`SYS_DEALLOC`	ptr	0, or -1 when `ptr` is not the start of a live block
14	`SYS_SOUND`	buf, len	bytes queued for oljud, or the bytes still waiting when `buf` is 0, or with `len` -1 as well, stops all sound and returns what was dropped, and -1 with no sound card
15	`SYS_WRITEFILE`	name, buf, len	`len`, or -1
16	`SYS_SLEEP`	ticks	0, after the ticks have passed
17	`SYS_ARGC`	none	how many arguments the task was started with
18	`SYS_ARGV`	i	argument `i` in the task's own memory, or 0
19	`SYS_LISTDIR`	path, buf, max	how many entries were written, or -1 when the path is not a directory
20	`SYS_SPAWN`	line	the new task's id, or a negative error
21	`SYS_PROTECT`	addr, pages, mode	0, or -1 when a page is not the task's own heap

the drawing calls take coordinates relative to the program's own window. a program draws a whole frame into its own buffer and shows it with one SYS_PRESENT, which is also why SYS_GLYPH hands over a font bitmap instead of drawing text. keys reach a program only while its tavla has focus, through a queue of its own.