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Fano-plane palette scheme: the 7 colors map onto 7 CGB BG palettes so
any color pair shares one palette; a tile's palette is picked from the
set of colors its two cells need (tables generated by tools/gencolor.py).
Per cell a packed (bg<<4)|fg byte lives alongside the char shadow, and
the glyph blitter steers glyph/empty pixels to each cell's fg/bg color
slots via plane masks.
An ANSI-ish CSI parser (ESC [ .. m) drives it; usr/ansi.c demos it and
the irc client now renders hashed nick colors, status dimming and a
channel-activity bar.
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The kernel had no clock: TimerISR was a reti stub, IEF_TIMER masked, and
IME was never enabled - the vectors were decorative. sys_sleep just polls
DIV deltas per-process; nothing counted globally.
Now: TAC runs the hardware timer at 16384 Hz with TMA=0, so TIMA overflows
at exactly 64 Hz; TimerISR increments a monotonic 32-bit wTicks (wraps
after ~2.1 years). Scheduling stays cooperative - the ISR is transparent.
Enabling IME in a kernel written for zero interrupts needs care wherever
SP points into memory whose bank is being switched (an IRQ pushes onto SP):
- read_block/write_block map the disk bank over the $A000 window that
holds the caller's stack -> di/ei around the transfer (~2ms, well under
the 15.6ms tick period, so no tick is ever lost)
- hSwitchTo switches SVBK + cart-RAM banks under the outgoing stack ->
di on entry, ei once the incoming stack is mapped
- fork already runs on KSTACK_TOP2 (fixed WRAM) - safe as-is
- term_putc's SVBK switch only remaps $Dxxx, stacks live in $Axxx/$Cxxx
SYS_UPTIME (36) copies the counter (4B LE, di/ei so the read can't tear)
to a user buffer; libc gticks(); usr/uptime.c formats 'up [Nd] H:MM:SS'.
uptime avoids SDCC long div/shift entirely: sm83.lib modules link into
their own areas that land in the $A000 RAM window (latent build.sh trap,
documented there) - bytewise >>6 plus bounded subtraction loops instead.
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Userland sources live in usr/ (fits the Unix theme better than 'c').
SDCC output .bin blobs land in build/usr/ with the other build artifacts
instead of littering the source dir; programs.asm INCBINs them from there.
Byte-identical ROM.
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irc HOST [NICK] - connects over the kernel TCP stack (DNS-resolves the
host), registers, and runs a live client on the 40x18 LCD.
UI, within the terminal's means (no cursor addressing - just \r + \b):
messages scroll above a fixed irssi-style input line '[#chan] text_'
redrawn in place; long input scrolls horizontally. The elders' formats:
<nick> msg, <nick:#c> off-channel, *nick* private, -nick- notice,
* nick action, >target< outbound, -!- server/status. Keys come from both
the OSK (SELECT) and the console ring (pollcon), so a hub can drive it.
Commands: /join /part /msg /me /nick /quit /raw, plus bare text to the
current channel. Handles PING (PONG + a wink), CTCP ACTION/VERSION,
JOIN/PART/QUIT/KICK/NICK, 332/353 topic+names, and 433 nick-in-use
(auto-appends _). Registers on bank 32 as program id 30.
Note: gbos doesn't zero C statics, so main() inits its state explicitly;
the local TCP port is randomized (DIV) to dodge a stale server-side
half-open from an unclean prior exit. Tested end to end against a small
ircd through gbhub: full MOTD burst, join, channel + private messages,
actions, and bot replies all render correctly.
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The address is no longer baked in. net_init starts at 0.0.0.0; a DHCP client
runs as the first thing on boot (init/shell forks it and waits), and only once
it has a lease (or gives up) does the prompt appear.
Kernel:
- IP is configurable: 0.0.0.0 until leased; NET_SETIP op stores it.
- 16-bit frame length. DHCP/BOOTP packets are ~272 bytes, over the old 255-byte
frame cap, so net_slip_send takes a 16-bit length, net_pump assembles into a
320-byte buffer with a 16-bit wNetRxLen, and udp_send writes a 16-bit IP total.
Payloads stay <=255 (kept small on purpose) so the per-protocol datalen math
is unchanged. wNetTx/wNetRxBuf 256->320, SK_RXBUF 208->288.
Userland:
- c/dhcp.c: DISCOVER->OFFER->REQUEST->ACK over a UDP socket, then net_setip();
times out gracefully (shell still boots) if there's no server. sh.c runs it
before the prompt.
Bridge (self-contained DHCP server, no dnsmasq):
- tunbridge.py + netboot intercept UDP->:67 and answer OFFER/ACK leasing
10.0.0.2 (gateway 10.0.0.1); everything else is bridged/NATed as before.
Regression-tested ICMP/UDP/TCP after the 16-bit change. Verified end to end:
dhcp: discovering
dhcp: leased 10.0.0.2
/# ping 10.0.0.1 -> 4/4 (traffic from the leased address)
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Adds UDP to the kernel socket layer on top of the ICMP core:
- net_sum() (raw folded sum) split out of net_cksum() so a UDP pseudo-header
(src/dst IP + proto + length) can seed the segment checksum.
- udp_send: builds IP+UDP with the pseudo-header checksum; NET_BIND sets the
local/source port; net_connect sets the peer.
- udp_in: demuxes inbound UDP by destination port to the bound socket
(net_find_udp), delivers the payload + source addr.
Also fixes a real recv bug: net_pump clobbers BC/DE/HL, so the old recv timeout
counted in registers and was effectively random. recv now counts in WRAM.
New `nslookup HOST` (PROG_NSLOOKUP=28, bank 30): builds a DNS A query and parses
the answer (with 0xC0 name-compression) entirely in userland over a UDP socket -
the kernel never sees DNS, just UDP. Verified through the bridge NAT:
/# nslookup example.com -> example.com -> 172.66.147.243
This gives us name resolution for the TCP/HTTP demo next.
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New `ping [A.B.C.D]` program (PROG_PING=27, bank 29): builds and sends ICMP
echo requests from 10.0.0.2, then reads replies off the link port. It keeps
reading SLIP frames until it finds *our* echo reply, skipping the IGMP/mDNS/
SSDP multicast noise that shares 10.0.0.0/24. Reply wait uses a generous
srecv_nb spin budget since the emulator runs uncapped (no timer syscall yet).
Verified over the tunbridge (with NAT):
/# ping 10.0.0.1 -> 4/4 received, ttl=64 (the SLIP peer/host)
/# ping 1.1.1.1 -> 4/4 received, ttl=56 (Cloudflare, real net!)
ttl=56 is a real internet round trip (64 minus the hops). Combined with the
host being able to ping the GB, the Game Boy is now a full two-way ICMP host.
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Start of an actual TCP/IP stack on gbos (TLS stays in a proxy). netd is a
userland IP responder over SLIP: our address is 10.0.0.2, the SLIP peer
10.0.0.1. It parses IPv4 headers, answers ICMP echo requests, and rebuilds
the packet with correct IP + ICMP checksums (RFC 1071 one's-complement sum,
carry-folded - works fine on the SM83).
c/netd.c + register; tools/gateway.py gains --mode ping: it crafts ICMP echo
requests over SLIP and verifies the replies.
Verified: `netd` answers 4 pings, gateway reports reply from 10.0.0.2 with
cksum=ok for each. Next: UDP, then TCP.
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The application layer of the link-port demo, and it ties the whole system
together: the LCD terminal displays, the on-screen keyboard types, and the
link port carries a live chat.
Kernel: sys_srecv_nb (non-blocking link receive; A=byte, CF=none) and
sys_pollin (poll the OSK for a typed char without blocking) - syscalls
31/32. Both are what a poll loop needs to receive and type at once.
Userland: c/chat.c runs a poll loop - it feeds non-blocking bytes through a
SLIP receive state machine and prints whole incoming frames as messages,
while pollin() drives the on-screen keyboard; SELECT shows the keys, type a
line, START sends it as a frame. libc srecv_nb()/pollin().
Host: tools/gateway.py --mode chat is a simple bot peer (echoes each GB
message and injects a few async ones); --keys can drive the OSK for tests.
Verified: the gateway pushes 'welcome', '<alice> hey gameboy!', '<bob> nice
link cable' unprompted and the GB displays all three (async receive); typing
'hi' on the OSK echoes it and emits the SLIP frame \xC0hi\xC0 (send). A Game
Boy in the chat, keyboard on screen, over the link cable.
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Grow the link-port demo from echo to actual network access. The Game Boy
still only does SLIP framing + display; the host gateway does DNS/TCP/HTTP.
- c/netlib.h: SLIP framing factored out (header-only, per-program copy).
necho.c now uses it too.
- c/wget.c: `wget URL` frames the URL, then prints the reply body. The
gateway streams the body back as typed frames: 'D'<chunk> ... 'E'.
- tools/gateway.py: add --mode http (urlopen the frame as a URL, cap the
body, chunk it) alongside --mode echo; --cmd runs any gbos command.
Verified: `wget example.com` streams back the full Example Domain HTML onto
the terminal; `wget sl0p.foo` fetches the real page. A Game Boy on the web,
over the link cable.
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First step of link-port networking. The LCD terminal + OSK freed the serial
port from console duty, so it can be the network link.
Kernel (src/net.asm): raw link-port serial that bypasses the console/
terminal - sys_ssend (transmit, GB drives the clock) and sys_srecv (receive,
GB slave, blocks by yielding). Syscalls 29/30.
Userland: libc ssend()/srecv(); c/necho.c does SLIP (RFC 1055) framing over
them - send a packet, receive the reply, print it.
Host: tools/gateway.py wraps the emulator, owns its link serial, speaks SLIP,
and (for now) echoes every frame back - the "link cable adapter". Console
(ASCII) bytes on the same channel are printed for visibility.
Verified: `necho` sends a SLIP frame, the gateway decodes+echoes it, and gbos
prints the reply - a real framed round-trip over the Game Boy link port.
Next: swap the echo for actual network ops (DNS/HTTP or IRC/chat).
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Replace the shell's temp-file pipe hack with proper in-kernel FIFOs.
Kernel (src/pipe.asm, new):
- A small pool of bounded ring buffers (PIPE_MAX=2, 64 B each) with
writers/readers refcounts. Pipe fds are $F0+idx*2 (read) / +1 (write);
$FF stays "console".
- SYS_PIPE allocates one (writers=readers=1) and returns the read fd
(write = read+1). getb/putb/close dispatch pipe fds here; sys_exit drops
the refcounts held as PROC_STDIN/PROC_STDOUT.
- Blocking with SchedYield, which is the flow control: read blocks while
empty with a writer (EOF once writers hit 0), write blocks while full
with a reader, and if the last reader is gone the writer is killed
(SIGPIPE -> exit 141). Cooperative-scheduler friendly.
Shell (c/sh.c):
- run_pipeline(): split on '|', make a pipe between adjacent stages, and
fork ALL stages concurrently (no wait between), wiring stdin/stdout;
then wait for all. Per-stage >/< still honored; orphaned pipe ends are
closed on a lookup miss so EOF/EPIPE propagate.
- Drop the __pipe temp file and its 2 KB / serialized limits.
libc: pipe(). New c/ptest.c exercises the FIFO (write, read back, EOF).
Now works (old version couldn't): multi-stage a|b|c; streaming beyond 2 KB
(count 120 | wc = 3372 bytes through a 64 B buffer); early-exit SIGPIPE
(count 200 | true kills count instead of hanging/overflowing a file).
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The terminal now has a variable usable height (wTermRows). term_scroll and
cursor_down operate within [0 .. wTermRows-1], and term_set_rows(n) shrinks
or grows that region, scrolling the cursor up into view when it would fall
outside. osk_toggle shrinks the terminal to the rows above the keyboard on
show (18 - OSK_ROWS = 15) and restores full height on hide, so the active
line is always visible just above the docked keyboard, and hiding the OSK
reclaims all 18 rows.
Also add c/count.c ("count [n]", default 25): prints n numbered lines to
observe/debug scrolling and the scroll-region behavior. Registered as
program id 21 / bank 23. Fixed the arg to read argv[0] (getargs returns the
string after the command name).
Verified: filling the screen then opening the OSK scrolls the latest line
to row 14 (visible) with the keyboard at 15-17; closing it restores rows
15-17; count N prints exactly N lines.
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Add a background-tile text terminal that packs TWO 4px-wide characters
into each 8x8 tile, giving a 40x18 grid instead of the 20x18 you'd get
from an 8x8 font. The tilemap is static (one dedicated VRAM tile per
screen position); we rebuild a tile's 16 bytes from two glyphs whenever
a character changes. 360 tiles exceed the 256 a single tilemap can
address, so positions 256-359 live in VRAM bank 1 via the CGB tilemap
attribute bank-bit -- hence CGB-only.
- Switch the ROM to CGB (rgbfix -C). Safe for the FS: every process has
PROC_WRAMB=1, so SVBK stays on bank 1 and the WRAMX FS caches don't move.
- CGB BG palette 0 = white bg / black text via BCPS/BCPD.
- src/term.asm: term_init (palette + static tilemap + clear buffer),
build_tile (combine two 4px glyphs -> one 8x8 tile, correct VRAM bank),
term_redraw (rebuild all tiles), term_puts, term_show, term_test.
- src/font.asm: 96-glyph 3x5-in-4x8 font, generated by tools/genfont.py.
- 40x18 text buffer at $D600 (WRAMX, above the FS caches).
- tools/ppmview.py: render a --shot PPM as ASCII so the LCD is inspectable
from the shell during development.
Verified via emulator screenshot: "GBOS TERMINAL", the alphabet, and a
bank-1 row all render legibly at 40 columns. Serial shell + filesystem
still work unchanged.
Note: a full term_redraw builds 360 tiles and takes ~8 frames; fine for
incremental single-char updates, but scrolling needs a smarter path
(next milestone). Input (no keyboard) is also still TODO.
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- directories generalized: dir_find/dir_add/dir_remove take any dir inode;
every dir carries '.'/'..'. Path resolution (resolve / resolve_parent) walks
absolute or cwd-relative paths; open/mkdir/chdir/remove/opendir take paths.
- per-process cwd: PROC_CWD in the PCB (root by default, inherited on fork);
sys_chdir sets it, sys_opendir points ls at any directory.
- shell: 'cd' builtin + cwd-aware prompt; 'mkdir'/'ls <dir>' tools; 'exit'/'quit'
and EOF call poweroff() (clean shutdown via the $ED opcode -> reliable save).
- three HL/buffer-clobber bugs fixed along the way: resolve didn't preserve the
path cursor across dir_find; cur_cwd clobbered HL; resolve_parent set the final
name before resolve() overwrote wFsNameBuf (now copied after).
- verified: nested mkdir/cd/save, multi-level paths (cat docs/sub/b), and the
whole tree persists across a reboot.
- README: document directories + the poweroff opcode.
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- blk.asm: read_block/write_block move 256-byte blocks between battery-backed
cart-RAM banks (8-11, the 'disk') and a WRAM bounce buffer. Banking is hidden
in those two routines; they inline the 'restore my bank' step so they never
touch the stack while the disk bank is mapped over the process's $A000 window
(the stack lives there too -- a call/ret would rug-pull it).
- format-on-first-boot: superblock magic in block 0; otherwise the disk persists.
- cart RAM bumped to 128 KiB (-r 4); process banks 0-7, disk banks 8-11.
- debug tool 'blk fill/peek' + syscalls to validate round-trip and persistence.
- verified: round-trip incl. cross-bank (block 100 -> bank 11); block survives a
reboot via .sav; magic intact (no reformat on 2nd boot).
- old WRAM 8-slot FS still backs the tools until stages 2-3.
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- sys_reap: nohang reap of a finished zombie child (-> pid or 0).
- shell: 'cmd &' launches in the background (prints [pid], no wait); reaps
finished jobs at the prompt ([pid done]). Foreground now waits for its own
child specifically (loops wait(), reporting bg completions meanwhile) so kill
reports the right pid.
- spin: a process that yields forever - a target for ps/kill.
- verified: spin &; ps shows it; kill <pid> removes just that one; immortal
init; self-finishing bg worker reaped with [pid done].
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- PCB gains PROC_PROG (running program id), set by exec, inherited on fork.
- sys_kill(pid): reject pid 1 (immortal) and unknown/dead pids; mark the target
zombie, reparent its children to init, wake its parent if blocked in wait;
schedule away if a process kills itself. Reuses FindPcbByPid/ReparentToInit.
- sys_ps(slot,buf)->{pid,state,prog}; sys_progname(id) via NameTable reverse
lookup. NameTable gains sh/ps/kill.
- libc: kill/psget/progname; tools ps (pid state cmd) and kill <pid>.
- verified: ps lists sh(B)+ps(R); kill 1 refused; kill 42 fails.
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- kernel I/O routing: PCB gains PROC_STDIN/PROC_STDOUT (default console $FF),
inherited across fork. KGetc/KPutc route read/write/putc to the console or a
file fd. New syscalls: putc(16), setin(17), setout(18), lookup(19).
read/write now go through the routing; putc/puts/nl use SYS_PUTC.
- sys_lookup + NameTable move command-name resolution into the kernel.
- shell rewritten in C (c/sh.c): tokenizes a line, parses > / < / |, and drives
fork+setin/setout+exec+wait. Pipes run as 'a > __pipe ; b < __pipe' (temp
file). asm shell + cmdtab removed; StrEqual/SkipName kept for sys_lookup.
- libc: fork/exec/wait/setin/setout/lookup wrappers.
- verified: echo>file, cat file, wc<file, cat readme|wc -l, echo ...|wc.
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- fs.asm: 8-slot RAM filesystem in WRAMX ($D000-$DFFF), name[8]+len[2]+data[502];
syscalls open/close/getb/putb/list/remove, seeded with a 'readme' at boot.
- libc: open/close/fgetc/fputc/flist/fremove wrappers + O_READ/O_WRITE/NOFD.
- tools: ls, save (stdin->file, one line), rm; cat/wc/head now take a file arg.
- fix: syscall dispatch clobbers A, so putb takes its byte in E (was reading the
handler's low address byte, 0xDC); ls NUL-terminates 8-char names.
- verified: save/cat/ls/rm cycle; wc readme -> '2 7 38'; head -n 1 readme.
- README: document the filesystem + the A-clobber ABI note.
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- c/libc.c: shared C helpers linked into every program - putu (print decimal),
atou (parse decimal), argv_parse (tokenize getargs() into argc/argv).
- wc: count lines/words/chars of stdin. head [n]: first n lines (drains rest to
EOF). args: argc/argv demo.
- pid now uses libc putu; build.sh links libc.c; Makefile CBLOBS + libc dep.
- README: document the new tools + argv_parse.
- verified: 'args one two three' -> argc=3/argv[..]; wc '2 3 16'; head 2.
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- libc: add putc, puts, strlen, getargs (args string), EOF (=4) for readc.
- args: shell splits the command line at the first space ("cmd\0args\0" at
$A000, inherited by the child via fork); getargs() returns the arg string.
- shell: exit on Ctrl-D/EOF; $ prompt over a clean read loop.
- tools (c/): echo (argv), cat (stdin->stdout to EOF), uname, pid (decimal
print), true, false. Each built to a ROM-bank blob and registered.
- Makefile: CBLOBS list builds all C programs.
- README: document libc + the tool set.
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- c/{gbos.h,crt0.s,libc.s,build.sh}: SDCC sm83 -> ROM-bank blob toolchain.
libc syscall wrappers save/restore BC/DE/HL around rst $30 (trap clobbers
them; SDCC expects them preserved).
- build via SDCC native asxxxx path (sdasgb/sdldgb), crt0 linked first so
_start is the $4000 entry; blob INCBIN'd into a ROM bank.
- chello.c: prints a message + getpid() -> runs as 'chello' shell command.
- Makefile: auto-build c/*.bin, track as a dep of programs.o; gitignore blobs.
- README: document the C toolchain + the SDCC --asm=rgbds codegen bug that
forced the native-toolchain approach.
- verified: '$ chello' -> 'hello from C on gbos!' / 'my pid is 2'.
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