net: pump the network from the console wait (answer pings at the prompt)

A Game Boy sitting at the shell prompt now services the network instead of
being deaf until you run netd: KGetc (the console input wait) pumps net_pump
each poll, so inbound pings are auto-answered while idle. net_pump gained an
in-frame model and routes any non-framed link bytes to a small console-input
ring (con_push/con_pop), so a headless-injected command still reaches the shell
while SLIP frames go to the stack. Removes the old SLIP-skip-in-KGetc hack.

Verified: two Game Boys on the hub, GB0 idle at the prompt (no netd), GB1
`ping 10.0.0.2` -> 4/4 replies, routed GB1->hub->GB0->hub->GB1.

(Separate, pre-existing: gbhub *spawn* mode and windowed gbjoin can drop an idle
link socket - under investigation; daemon mode + headless is solid.)

3 files changed, 85 insertions, 42 deletions

diff --git a/src/kdata.asm b/src/kdata.asm
index eece708..83ed162 100644
--- a/src/kdata.asm
+++ b/src/kdata.asm
@@ -56,7 +56,6 @@ wFsPath::    DS 40      ; kernel-side copy of a path argument
 wFsSlashPtr::DS 2       ; last '/' seen while splitting a path
 wListDir::   DS 1       ; directory sys_list enumerates
 wKChar::     DS 1       ; scratch for KPutc
-wConInSkip:: DS 1       ; console input: mid-SLIP-frame? (skip net packets)
 wSleepTarget::DS 1      ; sys_sleep: target in 1/64-second units
 wSleepAcc::   DS 2      ; sys_sleep: accumulated DIV ticks
 wSleepLastDiv::DS 1     ; sys_sleep: previous DIV reading
diff --git a/src/socket.asm b/src/socket.asm
index 3b2b0c9..fa6b245 100644
--- a/src/socket.asm
+++ b/src/socket.asm
@@ -52,6 +52,10 @@ wNetTx::       DS 320      ; tx build buffer
 wNetRxBuf::    DS 320      ; rx frame assembly / parse
 wNetRxLen::    DS 2        ; 16-bit: frames can exceed 255 bytes (DHCP/BOOTP)
 wNetRxEsc::    DS 1
+wNetInFrame:: DS 1        ; net_pump: currently inside a SLIP frame?
+wConRing::    DS 16       ; console-input ring: non-framed bytes from the link
+wConHead::    DS 1
+wConTail::    DS 1
 wNetUdpPort::  DS 2      ; scratch: UDP dst port being demuxed
 wNetTO::       DS 3      ; recv timeout counter (net_pump clobbers registers)
 wNetTcpFlags:: DS 1      ; TCP flags for the segment being built
@@ -82,9 +86,56 @@ net_init::
     ld [wNetRxLen], a
     ld [wNetRxLen+1], a
     ld [wNetRxEsc], a
+    ld [wNetInFrame], a
+    ld [wConHead], a
+    ld [wConTail], a
     ld [wNetSeq], a
     ret
 
+; con_push(A) - queue a console-input byte (dropped if the ring is full)
+con_push::
+    ld b, a
+    ld a, [wConTail]
+    inc a
+    and 15
+    ld c, a
+    ld a, [wConHead]
+    cp c
+    ret z                       ; full -> drop
+    ld a, [wConTail]
+    ld e, a
+    ld d, 0
+    ld hl, wConRing
+    add hl, de
+    ld [hl], b
+    ld a, c
+    ld [wConTail], a
+    ret
+
+; con_pop -> A = byte, CF set if the ring is empty
+con_pop::
+    ld a, [wConHead]
+    ld b, a
+    ld a, [wConTail]
+    cp b
+    jr nz, .have
+    scf
+    ret
+.have
+    ld a, b
+    ld e, a
+    ld d, 0
+    ld hl, wConRing
+    add hl, de
+    ld c, [hl]
+    ld a, b
+    inc a
+    and 15
+    ld [wConHead], a
+    ld a, c
+    and a                       ; CF = 0
+    ret
+
 ; net_setip - store our IPv4 address (from wNetReq.NR_IP). Used by the DHCP
 ; client once it has a lease.
 net_op_setip:
@@ -757,14 +808,20 @@ udp_send:
 ; net_pump - read available serial bytes, assemble SLIP frames, process each.
 ; Non-blocking: returns when the link has no more bytes ready.
 ; =============================================================================
-net_pump:
+net_pump::
 .next
     call net_getbyte_nb
     ret c                       ; no byte ready
-    ; SLIP decode using wNetRxLen / wNetRxEsc
     cp SLIP_END
-    jr z, .frame
+    jr z, .delim
     ld c, a                     ; save byte
+    ld a, [wNetInFrame]
+    or a
+    jr nz, .inframe
+    ld a, c                     ; outside a frame -> console input
+    call con_push
+    jr .next
+.inframe
     ld a, [wNetRxEsc]
     or a
     jr nz, .escaped
@@ -816,25 +873,36 @@ net_pump:
     ld a, [wNetRxLen]           ; index++
     inc a
     ld [wNetRxLen], a
-    jr nz, .next
+    jp nz, .next
     ld a, [wNetRxLen+1]
     inc a
     ld [wNetRxLen+1], a
-    jr .next
-.frame
-    ; END: if we have a frame, process it and return (one frame per pump, so a
-    ; recv drains each segment before the next is delivered - no rx overwrite).
+    jp .next
+.delim
+    ; 0xC0 delimiter: end the current frame (process it) or start a new one.
     xor a
     ld [wNetRxEsc], a
+    ld a, [wNetInFrame]
+    or a
+    jr z, .startframe
     ld a, [wNetRxLen]
     ld hl, wNetRxLen+1
     or [hl]
-    jr z, .next                 ; empty frame, keep reading
+    jr z, .resetframe           ; empty frame
     call process_frame
+.resetframe
     xor a
+    ld [wNetInFrame], a
     ld [wNetRxLen], a
     ld [wNetRxLen+1], a
-    ret
+    ret                         ; one frame per pump
+.startframe
+    ld a, 1
+    ld [wNetInFrame], a
+    xor a
+    ld [wNetRxLen], a
+    ld [wNetRxLen+1], a
+    jp .next
 
 ; -----------------------------------------------------------------------------
 ; process_frame - IPv4 demux of the frame in wNetRxBuf (wNetRxLen bytes).
diff --git a/src/syscall.asm b/src/syscall.asm
index 1051a4d..2adf5bf 100644
--- a/src/syscall.asm
+++ b/src/syscall.asm
@@ -132,41 +132,17 @@ KGetc::
     call pad_poll               ; poll joypad; drive the on-screen keyboard
     call osk_handle             ; CF set + A = byte if a key was typed
     jr c, .done
-    ld a, $80
-    ld [rSC], a
-    ld a, [rSC]
-    bit 7, a
-    jr nz, .yield
-    ld a, [rSB]                 ; A = serial byte
-    ; The link port is also the network. Skip SLIP frames (0xC0-delimited) so
-    ; inbound packets never surface as console input; plain bytes (an injected
-    ; command in headless use) still pass through.
-    ld b, a
-    ld a, [wConInSkip]
-    or a
-    jr nz, .inframe
-    ld a, b
-    cp SLIP_END
-    jr z, .frameopen
-    ld a, b                     ; ordinary byte -> console input
-    jr .done
-.frameopen
-    ld a, 1
-    ld [wConInSkip], a
-    jr .poll
-.inframe
-    ld a, b
-    cp SLIP_END
-    jr nz, .poll                ; still inside a frame -> discard
-    xor a
-    ld [wConInSkip], a          ; frame end -> resume
+    ; The link port is the network. Pump it here so the Game Boy services the
+    ; net (answers pings, etc.) while sitting at the prompt; net_pump routes any
+    ; non-framed link bytes (a headless-injected command) to the console ring.
+    call net_pump
+    call con_pop                ; queued console byte? CF clear -> return it
+    jr nc, .done
+    call SchedYield
     jr .poll
 .done
     and a                       ; CF = 0 (not EOF)
     ret
-.yield
-    call SchedYield
-    jr .poll
 
 ; -----------------------------------------------------------------------------
 ; KPutc(E = byte) - write to this process's stdout (console/file).