refactor: c/ -> usr/, compiled program blobs out of the source tree

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.

41 files changed, 57 insertions, 56 deletions

diff --git a/.gitignore b/.gitignore
index bcba5ae..7d20801 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,3 @@
 build/
 *.gb
 *.sav
-c/*.bin
diff --git a/Makefile b/Makefile
index bc0eac7..9a7875b 100644
--- a/Makefile
+++ b/Makefile
@@ -17,17 +17,19 @@ all: $(ROM)
 $(BUILD)/%.o: src/%.asm | $(BUILD)
 	rgbasm $(ASFLAGS) -o $@ $<
 
-# C programs: compiled with SDCC into ROM-bank blobs and INCBIN'd by programs.asm
-CBLOBS := c/chello.bin c/echo.bin c/true.bin c/false.bin c/uname.bin \
-          c/pid.bin c/cat.bin c/wc.bin c/head.bin c/args.bin \
-          c/ls.bin c/save.bin c/rm.bin c/sh.bin c/ps.bin c/kill.bin c/spin.bin c/blk.bin c/mkdir.bin c/count.bin c/ptest.bin c/necho.bin c/wget.bin c/chat.bin c/netd.bin c/ping.bin c/nslookup.bin c/dhcp.bin c/irc.bin
+# Userland C programs (usr/): compiled with SDCC into ROM-bank blobs under
+# $(BUILD)/usr and INCBIN'd by programs.asm
+PROGS  := chello echo true false uname pid cat wc head args \
+          ls save rm sh ps kill spin blk mkdir count ptest necho \
+          wget chat netd ping nslookup dhcp irc
+CBLOBS := $(patsubst %,$(BUILD)/usr/%.bin,$(PROGS))
 $(BUILD)/programs.o: $(CBLOBS)
 
 # C programs also depend on the shared libc sources
-$(CBLOBS): c/libc.c c/gbos.h
+$(CBLOBS): usr/libc.c usr/gbos.h
 
-c/%.bin: c/%.c c/crt0.s c/libc.s c/build.sh
-	sh c/build.sh $< $@
+$(BUILD)/usr/%.bin: usr/%.c usr/crt0.s usr/libc.s usr/build.sh
+	sh usr/build.sh $< $@
 
 $(ROM): $(OBJS)
 	rgblink -m $(BUILD)/gbos.map -n $(BUILD)/gbos.sym -o $@ $(OBJS)
diff --git a/README.md b/README.md
index a968e4a..ea574bb 100644
--- a/README.md
+++ b/README.md
@@ -58,7 +58,7 @@ across a syscall (`push hl` / `pop hl`). Libc syscall stubs handle this for C.
 | 2 | read    | ✅ blocking console input (1 byte) via external-clock serial |
 | 4,5,9,10 | open/close/kill/brk | ⛔ `ENOSYS` |
 
-### The shell (`c/sh.c`)
+### The shell (`usr/sh.c`)
 
 init `exec`s the shell (written in C). It reads a line, tokenizes it, and runs
 commands with **I/O redirection and pipes**:
@@ -183,15 +183,15 @@ A real gbos would render to VRAM; serial is the zero-VRAM debug channel.
 ## Writing programs in C
 
 gbos programs can be written in **C**, compiled with **SDCC** (the `sm83` port).
-This makes porting tiny Unix CLI tools realistic. The toolchain (`c/`):
+This makes porting tiny Unix CLI tools realistic. The toolchain (`usr/`):
 
-- `c/gbos.h` — the userland API (`writes`, `readc`, `nl`, `getpid`, `sexit`).
-- `c/libc.s` — syscall wrappers (asxxxx asm). Each saves
+- `usr/gbos.h` — the userland API (`writes`, `readc`, `nl`, `getpid`, `sexit`).
+- `usr/libc.s` — syscall wrappers (asxxxx asm). Each saves
   `BC/DE/HL` around `rst $30`, since the trap clobbers them but SDCC expects
   them preserved.
-- `c/crt0.s` — entry: `call main`; then `exit(0)`. Linked first so `_start` is
+- `usr/crt0.s` — entry: `call main`; then `exit(0)`. Linked first so `_start` is
   the `$4000` entry.
-- `c/build.sh` — compiles a `.c` with SDCC's **native** toolchain
+- `usr/build.sh` — compiles a `.c` with SDCC's **native** toolchain
   (`sdasgb` + `sdldgb`), links code at `$4000`, and extracts the ROM-bank blob.
   The Makefile INCBINs it and registers it as a program.
 
@@ -206,9 +206,9 @@ void main(void) {
 
 ### libc
 
-Syscall wrappers (`c/libc.s`): `writes`, `putc`, `puts`, `nl`, `strlen`, `readc`
+Syscall wrappers (`usr/libc.s`): `writes`, `putc`, `puts`, `nl`, `strlen`, `readc`
 (returns `EOF`=4 at end of input), `getargs` (this program's argument string),
-`getpid`, `sexit`. C helpers (`c/libc.c`, linked into every program): `putu`
+`getpid`, `sexit`. C helpers (`usr/libc.c`, linked into every program): `putu`
 (print decimal), `atou` (parse decimal), `argv_parse` (tokenize into argc/argv).
 
 Arguments: the shell splits the command line at the first space and leaves
@@ -220,7 +220,7 @@ char *argv[8];
 unsigned char argc = argv_parse(argv, 8);   /* args one two -> argc=3 */
 ```
 
-### CLI tools (in `c/`)
+### CLI tools (in `usr/`)
 
 | tool | what it does |
 |------|--------------|
@@ -254,7 +254,7 @@ alpha
 beta
 ```
 
-Each tool is a separate `c/<name>.c`, built to a ROM-bank blob, INCBIN'd, and
+Each tool is a separate `usr/<name>.c`, built to a ROM-bank blob, INCBIN'd, and
 registered in the program table + shell command table (`src/programs.asm`).
 
 **Toolchain gotchas found the hard way:** SDCC's `--asm=rgbds` mode mis-orders
diff --git a/src/programs.asm b/src/programs.asm
index 36f9d02..92c736b 100644
--- a/src/programs.asm
+++ b/src/programs.asm
@@ -47,101 +47,101 @@ ProgHello:
 ; -----------------------------------------------------------------------------
 ; PROG_CHELLO (bank 5) - a program written in C, compiled with SDCC to a
 ; self-contained ROM-bank image (crt0 + libc + code) and included verbatim.
-; Rebuild with: sh c/build.sh c/chello.c c/chello.bin
+; Rebuild with: make (or: sh usr/build.sh usr/chello.c build/usr/chello.bin)
 ; -----------------------------------------------------------------------------
 SECTION "prog_chello", ROMX[$4000], BANK[5]
 ProgChello:
-    INCBIN "c/chello.bin"
+    INCBIN "build/usr/chello.bin"
 SECTION "prog_echo",   ROMX[$4000], BANK[6]
 ProgEcho:
-    INCBIN "c/echo.bin"
+    INCBIN "build/usr/echo.bin"
 SECTION "prog_true",   ROMX[$4000], BANK[7]
 ProgTrue:
-    INCBIN "c/true.bin"
+    INCBIN "build/usr/true.bin"
 SECTION "prog_false",  ROMX[$4000], BANK[8]
 ProgFalse:
-    INCBIN "c/false.bin"
+    INCBIN "build/usr/false.bin"
 SECTION "prog_uname",  ROMX[$4000], BANK[9]
 ProgUname:
-    INCBIN "c/uname.bin"
+    INCBIN "build/usr/uname.bin"
 SECTION "prog_pid",    ROMX[$4000], BANK[10]
 ProgPid:
-    INCBIN "c/pid.bin"
+    INCBIN "build/usr/pid.bin"
 SECTION "prog_cat",    ROMX[$4000], BANK[11]
 ProgCat:
-    INCBIN "c/cat.bin"
+    INCBIN "build/usr/cat.bin"
 SECTION "prog_wc",     ROMX[$4000], BANK[12]
 ProgWc:
-    INCBIN "c/wc.bin"
+    INCBIN "build/usr/wc.bin"
 SECTION "prog_head",   ROMX[$4000], BANK[13]
 ProgHead:
-    INCBIN "c/head.bin"
+    INCBIN "build/usr/head.bin"
 SECTION "prog_args",   ROMX[$4000], BANK[14]
 ProgArgs:
-    INCBIN "c/args.bin"
+    INCBIN "build/usr/args.bin"
 SECTION "prog_ls",     ROMX[$4000], BANK[15]
 ProgLs:
-    INCBIN "c/ls.bin"
+    INCBIN "build/usr/ls.bin"
 SECTION "prog_save",   ROMX[$4000], BANK[16]
 ProgSave:
-    INCBIN "c/save.bin"
+    INCBIN "build/usr/save.bin"
 SECTION "prog_rm",     ROMX[$4000], BANK[17]
 ProgRm:
-    INCBIN "c/rm.bin"
+    INCBIN "build/usr/rm.bin"
 SECTION "prog_ps",     ROMX[$4000], BANK[18]
 ProgPs:
-    INCBIN "c/ps.bin"
+    INCBIN "build/usr/ps.bin"
 SECTION "prog_kill",   ROMX[$4000], BANK[19]
 ProgKill:
-    INCBIN "c/kill.bin"
+    INCBIN "build/usr/kill.bin"
 SECTION "prog_spin",   ROMX[$4000], BANK[20]
 ProgSpin:
-    INCBIN "c/spin.bin"
+    INCBIN "build/usr/spin.bin"
 SECTION "prog_blk",    ROMX[$4000], BANK[21]
 ProgBlk:
-    INCBIN "c/blk.bin"
+    INCBIN "build/usr/blk.bin"
 SECTION "prog_mkdir",  ROMX[$4000], BANK[22]
 ProgMkdir:
-    INCBIN "c/mkdir.bin"
+    INCBIN "build/usr/mkdir.bin"
 SECTION "prog_count",  ROMX[$4000], BANK[23]
 ProgCount:
-    INCBIN "c/count.bin"
+    INCBIN "build/usr/count.bin"
 SECTION "prog_ptest",  ROMX[$4000], BANK[24]
 ProgPtest:
-    INCBIN "c/ptest.bin"
+    INCBIN "build/usr/ptest.bin"
 SECTION "prog_necho",  ROMX[$4000], BANK[25]
 ProgNecho:
-    INCBIN "c/necho.bin"
+    INCBIN "build/usr/necho.bin"
 SECTION "prog_wget",   ROMX[$4000], BANK[26]
 ProgWget:
-    INCBIN "c/wget.bin"
+    INCBIN "build/usr/wget.bin"
 SECTION "prog_chat",   ROMX[$4000], BANK[27]
 ProgChat:
-    INCBIN "c/chat.bin"
+    INCBIN "build/usr/chat.bin"
 SECTION "prog_netd",   ROMX[$4000], BANK[28]
 ProgNetd:
-    INCBIN "c/netd.bin"
+    INCBIN "build/usr/netd.bin"
 SECTION "prog_ping",   ROMX[$4000], BANK[29]
 ProgPing:
-    INCBIN "c/ping.bin"
+    INCBIN "build/usr/ping.bin"
 SECTION "prog_nslookup", ROMX[$4000], BANK[30]
 ProgNslookup:
-    INCBIN "c/nslookup.bin"
+    INCBIN "build/usr/nslookup.bin"
 SECTION "prog_dhcp",   ROMX[$4000], BANK[31]
 ProgDhcp:
-    INCBIN "c/dhcp.bin"
+    INCBIN "build/usr/dhcp.bin"
 SECTION "prog_irc",    ROMX[$4000], BANK[32]
 ProgIrc:
-    INCBIN "c/irc.bin"
+    INCBIN "build/usr/irc.bin"
 
 ; -----------------------------------------------------------------------------
-; PROG_SH (bank 3) - the shell, now written in C (c/sh.c): parses >/</| and
+; PROG_SH (bank 3) - the shell, now written in C (usr/sh.c): parses >/</| and
 ; drives fork+exec+wait with I/O redirection. Command lookup + StrEqual/SkipName
 ; live in the kernel now (sys_lookup + NameTable + shell_lib).
 ; -----------------------------------------------------------------------------
 SECTION "prog_sh", ROMX[$4000], BANK[3]
 ProgSh:
-    INCBIN "c/sh.bin"
+    INCBIN "build/usr/sh.bin"
 
 ; -----------------------------------------------------------------------------
 ; Shell string helpers (ROM0, always mapped).
diff --git a/c/args.c b/usr/args.c
index c6f4db3..c6f4db3 100644
--- a/c/args.c
+++ b/usr/args.c
diff --git a/c/blk.c b/usr/blk.c
index 36839c0..36839c0 100644
--- a/c/blk.c
+++ b/usr/blk.c
diff --git a/c/build.sh b/usr/build.sh
index 8034d87..93815d2 100755
--- a/c/build.sh
+++ b/usr/build.sh
@@ -1,15 +1,15 @@
 #!/bin/sh
 # Build a gbos C program into a self-contained 16 KiB ROM-bank image.
 # SDCC native toolchain; crt0 linked FIRST so _start is the $4000 entry.
-# usage: c/build.sh <prog.c> <out.bin>
+# usage: usr/build.sh <prog.c> <out.bin>     (run from the repo root)
 set -e
-SRC="$1"; OUT="$2"; B=build/c
+SRC="$1"; OUT="$2"; B=build/usr/obj
 LIBDIR=/usr/share/sdcc/lib/sm83
-mkdir -p "$B"
-sdasgb -o "$B/crt0.rel" c/crt0.s
-sdasgb -o "$B/libc.rel" c/libc.s
-sdcc -msm83 -c -Ic c/libc.c -o "$B/libc_c.rel"
-sdcc -msm83 -c -Ic "$SRC" -o "$B/prog.rel"
+mkdir -p "$B" "$(dirname "$OUT")"
+sdasgb -o "$B/crt0.rel" usr/crt0.s
+sdasgb -o "$B/libc.rel" usr/libc.s
+sdcc -msm83 -c -Iusr usr/libc.c -o "$B/libc_c.rel"
+sdcc -msm83 -c -Iusr "$SRC" -o "$B/prog.rel"
 # link: crt0 first (=> _start at 0x4000), then libc, program, and sm83 lib
 sdldgb -n -m -w -j -i "$B/prog.ihx" \
        -b _CODE=0x4000 -b _DATA=0xa000 \
diff --git a/c/cat.c b/usr/cat.c
index 790cb88..790cb88 100644
--- a/c/cat.c
+++ b/usr/cat.c
diff --git a/c/chat.c b/usr/chat.c
index 987b336..987b336 100644
--- a/c/chat.c
+++ b/usr/chat.c
diff --git a/c/chello.c b/usr/chello.c
index f570b61..f570b61 100644
--- a/c/chello.c
+++ b/usr/chello.c
diff --git a/c/count.c b/usr/count.c
index 37cdcce..37cdcce 100644
--- a/c/count.c
+++ b/usr/count.c
diff --git a/c/crt0.s b/usr/crt0.s
index 0d8371f..0d8371f 100644
--- a/c/crt0.s
+++ b/usr/crt0.s
diff --git a/c/dhcp.c b/usr/dhcp.c
index e4186f4..e4186f4 100644
--- a/c/dhcp.c
+++ b/usr/dhcp.c
diff --git a/c/echo.c b/usr/echo.c
index f8d5125..f8d5125 100644
--- a/c/echo.c
+++ b/usr/echo.c
diff --git a/c/false.c b/usr/false.c
index a124951..a124951 100644
--- a/c/false.c
+++ b/usr/false.c
diff --git a/c/gbos.h b/usr/gbos.h
index 2350665..2350665 100644
--- a/c/gbos.h
+++ b/usr/gbos.h
diff --git a/c/head.c b/usr/head.c
index 3298e54..3298e54 100644
--- a/c/head.c
+++ b/usr/head.c
diff --git a/c/irc.c b/usr/irc.c
index 250738a..250738a 100644
--- a/c/irc.c
+++ b/usr/irc.c
diff --git a/c/kill.c b/usr/kill.c
index e524627..e524627 100644
--- a/c/kill.c
+++ b/usr/kill.c
diff --git a/c/libc.c b/usr/libc.c
index a48a64c..a48a64c 100644
--- a/c/libc.c
+++ b/usr/libc.c
diff --git a/c/libc.s b/usr/libc.s
index 5b176d9..5b176d9 100644
--- a/c/libc.s
+++ b/usr/libc.s
diff --git a/c/ls.c b/usr/ls.c
index 0e2e01f..0e2e01f 100644
--- a/c/ls.c
+++ b/usr/ls.c
diff --git a/c/mkdir.c b/usr/mkdir.c
index c907518..c907518 100644
--- a/c/mkdir.c
+++ b/usr/mkdir.c
diff --git a/c/necho.c b/usr/necho.c
index 99551d4..99551d4 100644
--- a/c/necho.c
+++ b/usr/necho.c
diff --git a/c/netd.c b/usr/netd.c
index b07abd2..b07abd2 100644
--- a/c/netd.c
+++ b/usr/netd.c
diff --git a/c/netlib.h b/usr/netlib.h
index ec98eac..ec98eac 100644
--- a/c/netlib.h
+++ b/usr/netlib.h
diff --git a/c/nslookup.c b/usr/nslookup.c
index 6a531b8..6a531b8 100644
--- a/c/nslookup.c
+++ b/usr/nslookup.c
diff --git a/c/pid.c b/usr/pid.c
index 9e4e792..9e4e792 100644
--- a/c/pid.c
+++ b/usr/pid.c
diff --git a/c/ping.c b/usr/ping.c
index 8671318..8671318 100644
--- a/c/ping.c
+++ b/usr/ping.c
diff --git a/c/ps.c b/usr/ps.c
index 7bfc0de..7bfc0de 100644
--- a/c/ps.c
+++ b/usr/ps.c
diff --git a/c/ptest.c b/usr/ptest.c
index 88b7d30..88b7d30 100644
--- a/c/ptest.c
+++ b/usr/ptest.c
diff --git a/c/resolve.h b/usr/resolve.h
index 9aaccc1..9aaccc1 100644
--- a/c/resolve.h
+++ b/usr/resolve.h
diff --git a/c/rm.c b/usr/rm.c
index 25f3004..25f3004 100644
--- a/c/rm.c
+++ b/usr/rm.c
diff --git a/c/save.c b/usr/save.c
index 1755fea..1755fea 100644
--- a/c/save.c
+++ b/usr/save.c
diff --git a/c/sh.c b/usr/sh.c
index 3178894..3178894 100644
--- a/c/sh.c
+++ b/usr/sh.c
diff --git a/c/sock.h b/usr/sock.h
index 876e85c..876e85c 100644
--- a/c/sock.h
+++ b/usr/sock.h
diff --git a/c/spin.c b/usr/spin.c
index 2a3d4e8..2a3d4e8 100644
--- a/c/spin.c
+++ b/usr/spin.c
diff --git a/c/true.c b/usr/true.c
index 4cf437e..4cf437e 100644
--- a/c/true.c
+++ b/usr/true.c
diff --git a/c/uname.c b/usr/uname.c
index 511501d..511501d 100644
--- a/c/uname.c
+++ b/usr/uname.c
diff --git a/c/wc.c b/usr/wc.c
index 4fa48ee..4fa48ee 100644
--- a/c/wc.c
+++ b/usr/wc.c
diff --git a/c/wget.c b/usr/wget.c
index aafbae0..aafbae0 100644
--- a/c/wget.c
+++ b/usr/wget.c