usr: grep, more, cp, nc - and make pollcon pump the link

The shell has had pipes for a while with nothing to pipe *through*, and
an 18-row screen with no way to stop output scrolling off it.

- grep [-vin] PAT [file]: substring match (no regex), stdin or a file,
  grep(1)'s exit convention. The other end of the pipe, at last.
- more [file]: pages 17 lines at a time, --More-- bar in white-on-blue,
  any key pages, q quits. Counts *screen* rows, so wrapped lines pay
  their real cost. Keys come from pollin/pollcon, not stdin, so
  `cat big | more` still has a keyboard.
- cp SRC DST: the fs has rm/mkdir but no way to duplicate a file. mv is
  this plus rm (there is no rename). Rejects SRC == DST, which would
  otherwise truncate the source via O_WRITE before reading a byte.
- nc [-s] HOST PORT: raw TCP. Interactive (START sends the line with a
  CRLF, /q quits) or -s to pump stdin and print the reply with its own
  wall-clock idle timeout, because the kernel's blocking recv counts
  pumps, not seconds. Generalizes what chat/irc hardcode:
  `nc towel.blinkenlights.nl 23` works.

sys_pollcon now pumps the link before draining the console ring. The
ring is filled *by* net_pump, so a program that never touches the
network polled a ring nothing would ever fill: host-injected keys
(gbtype/gbdemo) hung `more` forever, and the Game Boy stopped answering
pings for as long as it ran. KGetc already pumps for this reason.

New tools take banks 35-38. Locals over statics in all four: a program's
_DATA starts at $A000, where the shell leaves the command line.

1 files changed, 9 insertions, 2 deletions

diff --git a/src/net.asm b/src/net.asm
index 8309242..a5f0210 100644
--- a/src/net.asm
+++ b/src/net.asm
@@ -56,9 +56,16 @@ sys_srecv_nb::
 
 ; sys_pollcon() -> A = a queued console-ring byte (link-injected input,
 ; e.g. gbhub 'type'), or 0 if none. Non-blocking twin of KGetc's con_pop
-; path: programs that own their main loop (irc) poll this alongside the OSK.
-; The ring fills during net pumps, which such programs do constantly.
+; path: programs that own their main loop (irc, nc, more) poll this alongside
+; the OSK.
+;
+; Pump the link first. The ring is filled BY net_pump, so a caller that never
+; touches the network (a pager, a game) would otherwise poll a ring nothing
+; ever fills - host-injected keys (gbtype/gbdemo) would hang it forever, and
+; the Game Boy would stop answering pings for as long as it ran. KGetc already
+; pumps for exactly this reason; pollcon now matches it.
 sys_pollcon::
+    call net_pump
     call con_pop
     ret nc                      ; got a byte
     xor a