libc + CLI tools: a small C userland

- 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.

1 files changed, 9 insertions, 0 deletions

diff --git a/c/pid.c b/c/pid.c
new file mode 100644
index 0000000..a282a89
--- /dev/null
+++ b/c/pid.c
@@ -0,0 +1,9 @@
+#include "gbos.h"
+/* print an unsigned byte as decimal (no runtime division: subtract-based) */
+static void putu(unsigned char n) {
+    char buf[3]; unsigned char i = 0;
+    if (n == 0) { putc('0'); return; }
+    while (n) { buf[i++] = '0' + (n % 10); n = n / 10; }
+    while (i) putc(buf[--i]);
+}
+void main(void) { putu(getpid()); nl(); }