| Commit message (Collapse) | Author | Age |
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An MBC5 cart has no RTC, so SNTP is the only route to a wall clock. ntpdate
does one 48-byte UDP exchange on port 123 and hands the stamp to the kernel;
SYS_SETTIME keeps it with the tick it arrived at, and SYS_GETTIME adds the
elapsed ticks back, so date(1) is just formatting.
/# ntpdate
ntpdate: clock set from pool.ntp.org
/# date
Sep 24 21:01:23 UTC 2026 (host said 21:01:26)
The clock does not survive a power cycle - which is exactly what /rc is for:
`ntpdate` there and the machine boots knowing the time.
All of it is bounded subtraction, no long division or shifts: SDCC pulls those
from sm83.lib, whose modules link into the $A000 RAM window. The month tables
are string literals for the same family of reason - an initialized array goes
to _INITIALIZED at $A000 and the image overflows its bank ("buffer too small"
out of makebin), which is how this first failed to link.
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- sort [-r] [-n]: everything in RAM, which bounds it - a task has 8 KiB and a
file caps at 3 KiB, so 96 lines of 2400 bytes with room for the stack.
Insertion sort over an index; at that size the simple thing is fast and
costs far less ROM. `uniq -c f | sort -n -r` finally works.
NB the key needs a scratch SLOT of its own: gt() compares table entries, so
reusing slot i as scratch overwrites the entries being shifted into it.
- cmp: reports the first differing byte, silent when the files match. There
was no way to check a copy on the machine - you had to haul both to a host.
- strings [-n N]: pairs with xxd now that /bin/<prog> is readable. It finds
"gbos sm83 (Game Boy Color)" inside /bin/uname.
- du [dir]: 256-byte blocks, the unit df and the filesystem use. Bytes
overflow - /bin alone is 52 x 16 KiB, which wrapped a 16-bit counter and
printed 32768. Recurses by re-opendir'ing, since the kernel keeps only one
"directory being listed" cursor.
- time CMD: 1/64 s resolution from the tick counter. It rebuilds the child's
command line at $A000 - which is its own argument area, so everything is
copied to the stack first.
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The terminal understood SGR and nothing else, so there was no way to erase the
screen - printing 18 newlines only scrolls the history up out of sight.
term_erase_all blanks the buffer, resets the colours, homes the cursor and
repaints; the CSI parser routes 'J' to it, and clear(1) is four putc calls.
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gbfs has carried I_NLINK since the beginning and nothing ever incremented it,
so a file could only have one name. SYS_LINK adds a second directory entry
pointing at the same inode: the data is stored once, and both names read it.
That makes rm's job different. It now decrements the link count and only frees
the inode and its blocks when the LAST name goes - removing one of two links
used to free blocks the other still pointed at.
Refused, with the reasons that matter here: linking a directory (it would make
a cycle the tree walkers cannot survive), an existing name, and anything under
/bin, which is ROM.
The syscall takes a request block because the trap needs HL for its dispatch
table - and ln copies both paths to the stack first, since that block is a
static living at $A000, on top of the command line it is reading.
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/# ls -l /bin > b
/# cut -d \s -f 1 b | uniq -c
52 -
- touch FILE...: gbfs has no timestamps (an MBC5 cart has no RTC), so touch
does the half that means something here - make an empty file. O_APPEND is
exactly right: it creates, and it does not truncate what is already there.
- tr [-d] SET1 [SET2]: ranges (a-z), -d to delete, and a short SET2 padded
with its last character, like tr(1). ASCII only - a 128-entry map.
- rev, uniq [-c]: one line each, from a file or stdin like the other filters.
Two things the tests caught. A bare "-" is a SET, not a flag, so `tr . -`
has to skip flag-matching only when a letter follows the dash. And uniq
compared an empty "line" against the last run at EOF and flushed a phantom
blank one - a stray "1" in uniq -c output.
tr and cut also take \s \t \n \r escapes, because the shell has no quoting:
`-d ' '` arrives as three tokens, so a space or tab delimiter was simply
untypeable. Shell quoting would be the better fix; this makes the tools
usable today without touching the parser.
Banks 49-53; 10 program slots left in the 1 MB ROM.
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The commands only existed in the kernel's program table, so the only way to
find out what the machine could do was to already know (or read the source).
They are now a directory in the tree:
/# ls / /# xxd -l 16 /bin/uname
bin 0000: cd 6b 43 06 00 0e 00 f7 .kC.....
readme 0008: 18 fe 47 0e 03 f7 c9 21 ..G....!
/# ls -l /bin | head -2
- 1 16384 worker
/bin is synthetic, not disk: dir_find resolves "bin" in the root to BIN_INO
and names inside it through the NameTable, so `ls /bin` lists exactly what the
shell can run - one table, one truth, no second list to keep in sync. The root
listing carries "bin" as a synthetic first entry so it is discoverable by
walking the tree.
A program image is inode BIN_FILE|progid: it stats as a 16 KiB file (a program
IS its ROM bank) and reads through rom_getb, which maps that bank, takes the
byte, and maps the CALLER'S text bank back before returning - the caller is
itself executing from $4000, so leaving the wrong bank mapped would return
into another program's code. Verified byte-for-byte against the host's view of
the blob. The tree is read-only: create/remove/write inside /bin all fail.
xxd grows -l (stop after N bytes), because a program image is 2048 dump lines
- more than a pipe's temp file can hold, let alone the screen.
Two traps worth remembering, both found the hard way here: `and BIN_FILE`
destroys A, so the inode must be reloaded before inode_ptr (missing it once
made ls -l stat inode 0 and call every file an empty non-directory); and ls
now copies its directory argument to the stack first, because stat()'s request
block is a static living at $A000 - on top of the command line it was reading.
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Eight bytes per line rather than the usual sixteen: offset + 8 hex pairs +
the ASCII column is 38 of the terminal's 40 columns, where 16 would wrap
every line and make the dump unreadable. -c overrides it.
No -s (skip): there is no seek syscall, so it streams from the start - the
same reason tail(1) has to keep a ring.
/# xxd h
0000: 48 65 6c 6c 6f 20 67 62 Hello gb
0008: 6f 73 0d 0a os..
blk(1) could already peek at raw disk blocks; nothing could look inside a
file. Verified against known bytes, from stdin, with -c, through a pipe, and
on a missing file.
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NICK overwrote the nick with whatever was asked for, so two clients could
both be "alice": /NAMES listed her twice and a private message only ever
reached whichever slot came first in the table.
- A nick already held by another client is refused with 433
ERR_NICKNAMEINUSE and the client keeps the one it had. Unregistered
clients simply stay unregistered until they pick a free one, which is what
every client already expects.
- A NICK from a registered client is a rename: it is announced to the client
and to its channel, so nobody's user list goes stale.
- IRC names fold case, so "Alice" is "alice" - for the uniqueness check, for
PRIVMSG by nick, and for channels ("#GB" is "#gb"). One irceq() replaces
the exact-match compare that was used for all three.
gbos's own irc(1) already retries 433 by appending '_', so two Game Boys with
the default nick now sort themselves out: verified with a GB running ircd, a
laptop client holding "sl0pboy", and a second GB arriving as "sl0pboy_" -
both in #gbos, messages crossing both ways.
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Filling in the core utilities the box was missing:
- ls -l: type, links and size, now that stat() exists. The screen is 40
columns, so it is "d 1 256 name", not the GNU sprawl. Sizes were
previously unknowable except one file at a time with wc -c.
- df: blocks and inodes, used and free, on the 32 KiB cart disk.
- mv: no rename syscall, so it is cp + rm - and the copy has to finish before
the source goes, or a failure loses the file.
- tail [-n N]: no seek syscall, so it streams the input through a ring of N
lines rather than jumping to the end. N is capped by that ring.
- tee: the missing half of a pipeline - `cat big | tee copy | wc -l`.
- sleep: the thing every script needs; the kernel counts 1/64 s ticks.
- help: lists every command the shell knows, walked out of the kernel's own
name table. The box previously had no way to tell you what it could do.
- poweroff: the only safe way to stop a gbos that has data on it. The cart's
battery RAM is written when the emulator exits cleanly, so killing it loses
the whole filesystem - it comes back "formatted". Found while testing /rc.
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`sh < file` already executed the file - and then powered the Game Boy off,
because the read loop treated EOF as "the machine is done". That is right for
init and wrong for everything else, so scripts were unusable.
A shell now asks isatty(): with stdin on a file it prints no prompt, does not
echo the script back, and exits at EOF. Only pid 1 on the console still powers
down. init also runs /rc at boot if the cart has one, so a Game Boy can come
up with its own startup script - verified across a real power cycle (write
/rc, poweroff, reboot the same cart, watch init run it).
`>>` appends instead of truncating, which is what makes writing that script on
the device possible in the first place.
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Four things userland had no way to ask for:
- SYS_STAT: type, link count, size and inode for a path. The trap needs HL
for its dispatch table, so a call taking both a path and an output buffer
passes a request block - the shape SYS_NET already established. usr/stat.h
wraps it, header-only like sock.h, because the block must live in the
caller's RAM.
- SYS_FSSTAT: blocks/inodes, total and free. The bitmaps are already cached
write-through in fs_bmbuf, so this is the popcount boot_fs already prints.
- SYS_ISATTY: is this process's stdin the console? The shell needs it to tell
an interactive session from a script.
- O_APPEND: open a file positioned at EOF. There is no seek syscall, so this
is the only way to add to a file - without it nothing running ON the Game
Boy can build a multi-line file, shell scripts included.
Together these back ls -l, df, and `>>`.
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/# ircd &
host$ irssi -c 10.0.0.2 /join #gbos
other GB$ irc 10.0.0.2 gb2 /join #gbos
Implements the subset a real client needs to get in and talk: NICK, USER,
PING/PONG, JOIN, PART, PRIVMSG/NOTICE (to a channel or to a nick), NAMES and
QUIT, with the 001/004/375/372/376 numerics clients wait for on registration,
353/366 on join, and 421 for anything else. One channel per client keeps the
bookkeeping in fixed-size tables; this is a handheld with 8 KiB of task RAM.
MAXCL is 3, bounded by the kernel socket table (listener + client each take a
slot, the rest left for other programs). A fourth client is refused and the
daemon keeps serving - which is how the ~30s close() stall turned up.
Every event is logged to the LCD, so the Game Boy shows its own server
traffic: "+ alice", "alice joined", "<alice> hello".
Verified with real clients over the hub: two and three simultaneous hosts
registering, joining, channel relay (sender not echoed to itself), private
messages by nick, PING/PONG, unknown-command numerics, QUIT propagation, the
overflow refusal, and a second Game Boy running gbos's own irc(1) in the same
channel as a laptop client - messages crossing both ways between them.
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A server could only ever hold ONE connection, which makes an ircd pointless:
listen() turned the listener into the connection, and net_find_tcp demuxed on
local port alone, so two clients on 6667 were indistinguishable.
- net_find_tcp now matches an established socket on the full four-tuple
(local port + peer IP + peer port) and only falls back to a LISTENing
socket when none matches.
- A SYN at a listener no longer consumes it: tcp_spawn_conn clones a new
socket (local port + owning pid, so exit/kill still reclaims it) and the
listener keeps listening. accept() returns that socket; closing it leaves
the listener alone. A full table drops the SYN, and the client's retransmit
is taken once a slot frees.
- tcp_peer_is_current preserves BC: net_find_tcp scans with the socket index
there, and the compare needs BC for the rx buffer base. Without this the
scan died at the first mismatching socket, so a second client's handshake
ACK never reached its socket and it hung in SYNRCVD - tcpdump showed our
SYN+ACK going out and the client's NICK retransmitted five times into
silence.
- listen() only conflicts with another LISTENER on the port; connections
share it by design now.
- MAX_SOCKS 4 -> 6 (listener + 3 clients + 2 spare; 537 bytes of WRAM0 still
free), and SK_ACC marks a spawned connection as not yet accepted.
tcp_close's settle is also time-boxed to ~250 ms of real time. It counted
PUMPS (8 x 8000), which is ~30s of wall clock when the peer never answers -
invisible with well-behaved peers, but a daemon refusing a client that stayed
connected froze itself, and every other client with it, for half a minute.
httpd keeps its listener open across requests now, so the next client's SYN
is accepted immediately instead of being dropped between close and re-listen:
three parallel clients go 0.1/1.1/2.1s -> 0.4/1.0/0.1s.
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/# httpd &
host$ curl http://10.0.0.2/ -> a listing of the cart RAM
host$ curl http://10.0.0.2/readme -> the file, from battery-backed SRAM
GET only. "/" serves /index.html if present, else a generated listing; any
directory lists with every entry linked, so you can click around a 1997
handheld's disk from a browser. Content type from the extension. No
Content-Length: HTTP/1.0 + Connection: close delimits the body by closing,
which suits a stack with one in-flight segment.
All output goes through one 200-byte buffer, so each net_send is a full
segment instead of one tiny segment per string.
It drains the whole request, not just the request line. That is not
politeness: leaving the rest unread means those segments are never
acknowledged, so the client retransmits headers for a minute, never sends
its FIN, and its dead connection keeps arriving at port 80 long after we
re-listen. One curl with 1.4 KB of headers stalled every following request
for 30-120s.
It deliberately does NOT read the keyboard either. Backgrounded - the useful
way to run it - every key it polled would be a key stolen from the shell's
prompt. It is a daemon: kill(1) stops it, and the kernel reclaims its socket.
Verified with curl: index, byte-exact file bodies, nested paths, directory
listings, 404, 501, a 1.4 KB request spanning segments, browser user-agents,
three parallel clients (0.1/1.1/2.1s), the shell staying usable alongside it,
and six kill/restart cycles - more than there are sockets.
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The stack could only ever dial out. Two new ops give it an ear:
- listen(sock, port): sockets demux on LOCAL PORT alone, so the listener IS
the connection - the SYN fills in the peer and the socket becomes the
connection. One at a time, re-armed by listening again after close, which
is all a 4-socket table can honestly promise. A second client's SYN is
dropped in silence; its retransmit is taken once we are free (~1s), so
three parallel clients complete in 0.1/1.1/2.1s.
- accept(sock): one RX pump per call, never blocks (like recv_nb), so a
server keeps its own main loop and stays killable.
- TCP_LISTEN/TCP_SYNRCVD in tcp_in: answer a SYN with SYN+ACK, become
established on the handshake's ACK, and process any data that ACK carries.
tcp_peer_is_current tells a peer's retransmitted SYN from a newcomer's.
Without it, "any SYN in SYNRCVD is a retransmission" let a second client
*hijack* a connection mid-request: the first client got its SYN+ACK, sent
its GET twice, and was never answered (found in a tcpdump of two parallel
curls).
listen() also refuses a port another socket already holds - two sockets on
one port silently black-hole the second listener, since demux takes the
first match.
Sockets now record the pid that opened them (SK_OWNER) and exit *and* kill
release them: with 4 slots, a few killed irc/nc/httpd runs used to leave the
box unable to open a socket at all until reboot.
tcp_close stops settling the moment the peer's FIN/ACK arrives instead of
burning its whole pump budget. It otherwise sits in FINWAIT for about a
second, and a server that closes and re-listens drops the next client's SYN
in that window: every request after the first paid a SYN retransmit.
1.1s -> 0.1s per request.
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The shell has had pipes for a while with nothing to pipe *through*, and
an 18-row screen with no way to stop output scrolling off it.
- grep [-vin] PAT [file]: substring match (no regex), stdin or a file,
grep(1)'s exit convention. The other end of the pipe, at last.
- more [file]: pages 17 lines at a time, --More-- bar in white-on-blue,
any key pages, q quits. Counts *screen* rows, so wrapped lines pay
their real cost. Keys come from pollin/pollcon, not stdin, so
`cat big | more` still has a keyboard.
- cp SRC DST: the fs has rm/mkdir but no way to duplicate a file. mv is
this plus rm (there is no rename). Rejects SRC == DST, which would
otherwise truncate the source via O_WRITE before reading a byte.
- nc [-s] HOST PORT: raw TCP. Interactive (START sends the line with a
CRLF, /q quits) or -s to pump stdin and print the reply with its own
wall-clock idle timeout, because the kernel's blocking recv counts
pumps, not seconds. Generalizes what chat/irc hardcode:
`nc towel.blinkenlights.nl 23` works.
sys_pollcon now pumps the link before draining the console ring. The
ring is filled *by* net_pump, so a program that never touches the
network polled a ring nothing would ever fill: host-injected keys
(gbtype/gbdemo) hung `more` forever, and the Game Boy stopped answering
pings for as long as it ran. KGetc already pumps for this reason.
New tools take banks 35-38. Locals over statics in all four: a program's
_DATA starts at $A000, where the shell leaves the command line.
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dhcp's recv times out only after ~250*65536 pumps x3 retries, so
fork()+wait() left the screen stuck at 'dhcp: discovering' with no
prompt whenever no DHCP server answered (raw emulator, no bridge).
Fork without waiting: the prompt is immediate, the lease (or 'no
offer') lands a moment later, and the job is reaped by the main loop.
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sys_write sets wBatch; render_cursor_tile - the single choke point all
of term_putc's visible mutations pass through - then marks a dirty
span (per LINE-SLOT, so spans survive scroll rotation for free)
instead of rendering. term_write_end renders every dirty tile exactly
once, then the cursor. Scrolls stay immediate (blank rebuild is cheap
and artifact-free); file-bound writes flush for free.
The enabler is in libc: puts() was a SYS_PUTC trap PER CHARACTER, so
almost no console output ever went through sys_write. It now issues
one SYS_WRITE for the whole string - one trap, one batch, and every
line-printer (echo, irc, the shell) gets the batched path.
Measured: 37-char write = 128k cycles (3.5k/char) vs ~8k/char down
the per-char trap path. Full demo passes; GIF regenerated.
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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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