gdb: Packet Acknowledgment
E.11 Packet Acknowledgment
==========================
By default, when either the host or the target machine receives a
packet, the first response expected is an acknowledgment: either '+' (to
indicate the package was received correctly) or '-' (to request
retransmission). This mechanism allows the GDB remote protocol to
operate over unreliable transport mechanisms, such as a serial line.
In cases where the transport mechanism is itself reliable (such as a
pipe or TCP connection), the '+'/'-' acknowledgments are redundant. It
may be desirable to disable them in that case to reduce communication
overhead, or for other reasons. This can be accomplished by means of
the 'QStartNoAckMode' packet; 
QStartNoAckMode.
When in no-acknowledgment mode, neither the stub nor GDB shall send
or expect '+'/'-' protocol acknowledgments. The packet and response
format still includes the normal checksum, as described in
Overview, but the checksum may be ignored by the receiver.
If the stub supports 'QStartNoAckMode' and prefers to operate in
no-acknowledgment mode, it should report that to GDB by including
'QStartNoAckMode+' in its response to 'qSupported'; qSupported.
If GDB also supports 'QStartNoAckMode' and it has not been disabled via
the 'set remote noack-packet off' command (Remote
Configuration), GDB may then send a 'QStartNoAckMode' packet to the
stub. Only then may the stub actually turn off packet acknowledgments.
GDB sends a final '+' acknowledgment of the stub's 'OK' response, which
can be safely ignored by the stub.
Note that 'set remote noack-packet' command only affects negotiation
between GDB and the stub when subsequent connections are made; it does
not affect the protocol acknowledgment state for any current connection.
Since '+'/'-' acknowledgments are enabled by default when a new
connection is established, there is also no protocol request to
re-enable the acknowledgments for the current connection, once disabled.
Info Catalog
gdb: Remote Non-Stop
gdb: Remote Protocol
gdb: Examples