   GDB Remote communication protocol.

   A debug packet whose contents are <data>
   is encapsulated for transmission in the form:

	$ <data> # CSUM1 CSUM2

	<data> must be ASCII alphanumeric and cannot include characters
	'$' or '#'.  If <data> starts with two characters followed by
	':', then the existing stubs interpret this as a sequence number.

	CSUM1 and CSUM2 are ascii hex representation of an 8-bit 
	checksum of <data>, the most significant nibble is sent first.
	the hex digits 0-9,a-f are used.

   Receiver responds with:

	+	- if CSUM is correct and ready for next packet
	-	- if CSUM is incorrect

   <data> is as follows:
   Most values are encoded in ascii hex digits.  Signal numbers are according
   to the numbering in target.h.

	Request		Packet

	set thread	Hct...		Set thread for subsequent operations.
					c = 'c' for thread used in step and 
					continue; t... can be -1 for all
					threads.
					c = 'g' for thread used in other
					operations.  If zero, pick a thread,
					any thread.
	reply		OK		for success
			ENN		for an error.

	read registers  g
	reply		XX....X		Each byte of register data
					is described by two hex digits.
					Registers are in the internal order
					for GDB, and the bytes in a register
					are in the same order the machine uses.
			or ENN		for an error.

	write regs	GXX..XX		Each byte of register data
					is described by two hex digits.
	reply		OK		for success
			ENN		for an error

        write reg	Pn...=r...	Write register n... with value r...,
					which contains two hex digits for each
					byte in the register (target byte
					order).
	reply		OK		for success
			ENN		for an error
	(not supported by all stubs).

	read mem	mAA..AA,LLLL	AA..AA is address, LLLL is length.
	reply		XX..XX		XX..XX is mem contents
					Can be fewer bytes than requested
					if able to read only part of the data.
			or ENN		NN is errno

	write mem	MAA..AA,LLLL:XX..XX
					AA..AA is address,
					LLLL is number of bytes,
					XX..XX is data
	reply		OK		for success
			ENN		for an error (this includes the case
					where only part of the data was
					written).

	continue	cAA..AA		AA..AA is address to resume
					If AA..AA is omitted,
					resume at same address.

	step		sAA..AA		AA..AA is address to resume
					If AA..AA is omitted,
					resume at same address.

	continue with	Csig;AA		Continue with signal sig (hex signal
	signal				number).

	step with	Ssig;AA		Like 'C' but step not continue.
	signal

	last signal     ?               Reply the current reason for stopping.
                                        This is the same reply as is generated
					for step or cont : SAA where AA is the
					signal number.

	detach          D               Reply OK.

	There is no immediate reply to step or cont.
	The reply comes when the machine stops.
	It is		SAA		AA is the signal number.

	or...		TAAn...:r...;n...:r...;n...:r...;
					AA = signal number
					n... = register number (hex)
					  r... = register contents
					n... = `thread'
					  r... = thread process ID.  This is
						 a hex integer.
					n... = other string not starting 
					    with valid hex digit.
					  gdb should ignore this n,r pair
					  and go on to the next.  This way
					  we can extend the protocol.
	or...		WAA		The process exited, and AA is
					the exit status.  This is only
					applicable for certains sorts of
					targets.
	or...		XAA		The process terminated with signal
					AA.
        or...           OXX..XX	XX..XX  is hex encoding of ASCII data. This
					can happen at any time while the program is
					running and the debugger should
					continue to wait for 'W', 'T', etc.

	thread alive	TXX		Find out if the thread XX is alive.
	reply		OK		thread is still alive
			ENN		thread is dead
	
	remote restart	RXX		Restart the remote server

	extended ops 	!		Use the extended remote protocol.
					Sticky -- only needs to be set once.

	kill request	k

	toggle debug	d		toggle debug flag (see 386 & 68k stubs)
	reset		r		reset -- see sparc stub.
	reserved	<other>		On other requests, the stub should
					ignore the request and send an empty
					response ($#<checksum>).  This way
					we can extend the protocol and GDB
					can tell whether the stub it is
					talking to uses the old or the new.
	search		tAA:PP,MM	Search backwards starting at address
					AA for a match with pattern PP and
					mask MM.  PP and MM are 4 bytes.
					Not supported by all stubs.

	general query	qXXXX		Request info about XXXX.
	general set	QXXXX=yyyy	Set value of XXXX to yyyy.
	query sect offs	qOffsets	Get section offsets.  Reply is
					Text=xxx;Data=yyy;Bss=zzz

	Responses can be run-length encoded to save space.  A '*' means that
	the next character is an ASCII encoding giving a repeat count which
	stands for that many repititions of the character preceding the '*'.
	The encoding is n+29, yielding a printable character where n >=3 
	(which is where rle starts to win).  Don't use an n > 126.

	So 
	"0* " means the same as "0000".
