filesystem: a RAM FS (WRAMX) + ls/cat/save/rm; wc/head read files

- 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.

1 files changed, 19 insertions, 0 deletions

diff --git a/c/save.c b/c/save.c
new file mode 100644
index 0000000..dd2b8cd
--- /dev/null
+++ b/c/save.c
@@ -0,0 +1,19 @@
+#include "gbos.h"
+/* save <name>: read one line from stdin and store it as a file. */
+void main(void) {
+    char *argv[4];
+    unsigned char argc = argv_parse(argv, 4);
+    unsigned char fd;
+    char c;
+    if (argc < 1) { puts("usage: save <name>"); nl(); return; }
+    fd = open(argv[0], O_WRITE);
+    if (fd == NOFD) { puts("save: cannot create"); nl(); return; }
+    for (;;) {
+        c = readc();
+        if (c == EOF) break;
+        putc(c);            /* echo */
+        fputc(fd, c);
+        if (c == '\n') break;
+    }
+    close(fd);
+}