net: proper socket API in the kernel (SYS_NET) - no more SLIP in userland

The network stack moves into the kernel. src/socket.asm owns SLIP framing,
IPv4, RFC1071 checksums, and ICMP; programs now speak a socket API through one
syscall (SYS_NET, DE=&netreq dispatched by op): net_socket/connect/send/recv/
close/poll (c/sock.h). No program touches SLIP, IP headers, or checksums.

- Socket table (4 sockets) + tx/rx buffers in WRAM0; our IP = 10.0.0.2.
- net_pump: drains the link, reassembles SLIP frames, demuxes IPv4. Inbound
  ICMP echo requests are auto-answered in-kernel, so the GB replies to pings
  whenever any process pumps RX.
- ICMP sockets: send() emits an echo request to the connected peer; recv()
  returns the matching reply (with a spin/yield timeout).

ping.c is now a ~15-line socket client; netd.c is just `for(;;){net_poll();
yield();}`. Verified over tunbridge:
    /# ping 1.1.1.1     -> replies from the real internet (kernel builds it all)
    host# ping 10.0.0.2 -> 4/4, 0% loss (kernel auto-answers)

Gotchas recorded: gbos.inc isn't a make dep (touch asm after editing); this
crt0 doesn't copy initializers (fill arrays at runtime); and the arg string at
0xA000 overlaps _DATA, so parse targets must sit past it (big buffer first).
UDP and TCP sockets build on this same core next.

1 files changed, 19 insertions, 66 deletions

diff --git a/c/ping.c b/c/ping.c
index 12dabd9..c98f106 100644
--- a/c/ping.c
+++ b/c/ping.c
@@ -1,17 +1,14 @@
-#include "netlib.h"
-/* ping - originate ICMP echo requests from the Game Boy (10.0.0.2) and print
-   the replies. Target defaults to 10.0.0.1 (the SLIP peer / host); with NAT on
-   the bridge it can reach real internet hosts too. Usage: ping [A.B.C.D] */
+#include "sock.h"
+/* ping - originate ICMP echo requests via the kernel socket layer. No SLIP,
+   no IP, no checksums here: the kernel owns all of that. Usage: ping [A.B.C.D]
+   (default 10.0.0.1, the SLIP peer/host; reaches real hosts through NAT). */
 
-static unsigned char pkt[128];
+/* rbuf is declared first (and large) so the parse target dst[] lands well past
+   the argument string the shell leaves at 0xA000 - writing dst must not clobber
+   the arg while we're still reading it. */
+static unsigned char rbuf[96];
 static unsigned char dst[4];
-
-static unsigned int sum16(unsigned char *d, unsigned int len, unsigned int sum) {
-    unsigned int w, i = 0;
-    while (i + 1 < len) { w = ((unsigned int)d[i] << 8) | d[i + 1]; sum += w; if (sum < w) sum++; i += 2; }
-    if (len & 1) { w = (unsigned int)d[len - 1] << 8; sum += w; if (sum < w) sum++; }
-    return sum;
-}
+static unsigned char payload[4];
 
 static unsigned char parse_ip(char *s, unsigned char *out) {
     unsigned char i, v;
@@ -24,77 +21,33 @@ static unsigned char parse_ip(char *s, unsigned char *out) {
     }
     return 1;
 }
-
 static void put_ip(unsigned char *ip) {
     unsigned char i;
     for (i = 0; i < 4; i++) { putu(ip[i]); if (i < 3) putc('.'); }
 }
 
-static void send_echo(unsigned char seq) {
-    unsigned int c;
-    pkt[0] = 0x45; pkt[1] = 0; pkt[2] = 0; pkt[3] = 28;   /* 20 IP + 8 ICMP */
-    pkt[4] = 0; pkt[5] = 0; pkt[6] = 0; pkt[7] = 0;
-    pkt[8] = 64; pkt[9] = 1; pkt[10] = 0; pkt[11] = 0;    /* TTL, proto ICMP */
-    pkt[12] = 10; pkt[13] = 0; pkt[14] = 0; pkt[15] = 2;  /* src 10.0.0.2 */
-    pkt[16] = dst[0]; pkt[17] = dst[1]; pkt[18] = dst[2]; pkt[19] = dst[3];
-    c = ~sum16(pkt, 20, 0); pkt[10] = (unsigned char)(c >> 8); pkt[11] = (unsigned char)c;
-    pkt[20] = 8; pkt[21] = 0; pkt[22] = 0; pkt[23] = 0;   /* echo request */
-    pkt[24] = 0x12; pkt[25] = 0x34; pkt[26] = 0; pkt[27] = seq;
-    c = ~sum16(pkt + 20, 8, 0); pkt[22] = (unsigned char)(c >> 8); pkt[23] = (unsigned char)c;
-    slip_send((char *)pkt, 28);
-}
-
-/* wait for the ICMP echo reply for 'seq', skipping unrelated frames (the shared
-   10.0.0.0/24 carries IGMP/mDNS/SSDP noise). Returns 1 on match, 0 on timeout.
-   The emulator runs uncapped, so the spin budget is generous to span the
-   wall-clock round trip through the host bridge. */
-static unsigned char ping_wait(unsigned char seq) {
-    unsigned int o, i;
-    unsigned char len = 0, c, ihl;
-    int b;
-    for (o = 0; o < 20; o++) {
-        for (i = 0; i < 60000; i++) {
-            b = srecv_nb();
-            if (b < 0) continue;
-            c = (unsigned char)b;
-            if (c == SLIP_END) {
-                if (len) {
-                    ihl = (unsigned char)((pkt[0] & 0x0f) << 2);
-                    if (len >= (unsigned char)(ihl + 8) && pkt[9] == 1
-                        && pkt[ihl] == 0 && pkt[ihl + 7] == seq) return 1;
-                    len = 0;                     /* not ours - keep waiting */
-                }
-                continue;
-            }
-            if (c == SLIP_ESC) {
-                c = srecv();
-                if (c == SLIP_ESC_END) c = SLIP_END;
-                else if (c == SLIP_ESC_ESC) c = SLIP_ESC;
-            }
-            if (len < 128) pkt[len++] = c; else len = 0;
-        }
-    }
-    return 0;
-}
-
 void main(void) {
     char *arg;
-    unsigned char seq, got = 0;
+    unsigned char s, seq, got = 0;
     arg = getargs();
     if (!arg || !*arg) { dst[0] = 10; dst[1] = 0; dst[2] = 0; dst[3] = 1; }
     else if (!parse_ip(arg, dst)) { puts("ping: bad address"); nl(); sexit(1); }
 
+    payload[0] = 'g'; payload[1] = 'b'; payload[2] = 'o'; payload[3] = 's';
+    s = net_socket(SOCK_ICMP);
+    if (s == 0xFF) { puts("ping: no socket"); nl(); sexit(1); }
+    net_connect(s, dst, 0);
+
     puts("PING "); put_ip(dst); nl();
     for (seq = 1; seq <= 4; seq++) {
-        send_echo(seq);
-        if (ping_wait(seq)) {
+        net_send(s, payload, 4);
+        if (net_recv(s, rbuf, sizeof(rbuf)) != 0xFF) {
             got++;
-            puts("  reply from "); put_ip(pkt + 12);
-            puts(" seq="); putu(seq);
-            puts(" ttl="); putu(pkt[8]); nl();
+            puts("  reply from "); put_ip(dst); puts(" seq="); putu(seq); nl();
         } else {
             puts("  seq="); putu(seq); puts(" timeout"); nl();
         }
     }
     puts("-- "); putu(got); puts("/4 received"); nl();
+    net_close(s);
 }