Re: generic_load: Add ``set remote {read,write}-packet-size NNNN''

[Andrew Cagney <ac131313 at cygnus dot com>]

Well,

After much feedback :-), I've reviewed the behavour of the commands and
consequently changed it to:

	set remote memory-{read,write}-packet-size {VALUE,fixed,limit}

The VALUE is either a ``limit'' or ``fixed''.  A ``limit'' is further
reduced by GDB being paranoid about overrunning the targets buffer.  A
fixed value bypasses that mechanism.  GDB's existing behavour is to
``limit'' the packet size and that is made the default.

The main motivation for the change is that my initial implementaton
would change the packet size whenever the architecture changed :-(.  The
new implementation is more transparent (?).  

For instance:

Initially the packet size is not set so the target default is used and
that can be changed to anything:

(gdb) show remote memory-read-packet-size
The memory-read-packet-size is 0.  Packets are limited to 400 bytes.
(gdb) set remote memory-read-packet-size 200
(gdb) show remote memory-read-packet-size
The memory-read-packet-size is 200.  Packets are limited to 200 bytes.
(gdb) set remote memory-read-packet-size 10000
(gdb) show remote memory-read-packet-size
The memory-read-packet-size is 10000.  Packets are limited to 400 bytes.

Fixing the packet size attracts a warning and a different show output:

(gdb) set remote memory-read-packet-size fixed
The target may not be able to correctly handle a memory-read packet size
of 200 bytes.
Change the packet size? (y or n) y
(gdb) show remote memory-read-packet-size 
The memory-read-packet-size is fixed at 200 bytes.
(gdb) set remote memory-read-packet-size limit
(gdb) show remote memory-read-packet-size
The memory-read-packet-size is 200.  Packets are limited to 200 bytes.
(gdb) set remote memory-read-packet-size 0
(gdb) show remote memory-read-packet-size
The memory-read-packet-size is 0.  Packets are limited to 400 bytes.

Changing the architecture leads to fairly consistent behavour (say there
are two architectures byte50 and byte60):

(gdb) set remote memory-read-packet-size fixed
...
(gdb) set remote memory-read-packet-size 100
(gdb) set architecture byte50
(gdb) show remote memory-read-packet-size
The memory-read-packet-size is fixed at 100 bytes.
(gdb) set architecture byte60
(gdb) show remote memory-read-packet-size
The memory-read-packet-size is fixed at 100 bytes.
(gdb) set remote memory-read-packet-size limit
(gdb) show remote memory-read-packet-size
The memory-read-packet-size is 100.  Packets are limited to 60 bytes.
(gdb) set architecture byte50
(gdb) show remote memory-read-packet-size
The memory-read-packet-size is 100.  Packets are limited to 50 bytes.

More importantly the sequence:

	set remote .... NNN
	file ZYX

and

	file ZYX
	set remote .... NNN

now have identical behavour.

Thoughts.  Better names?

	Andrew


Andrew Cagney wrote:
> 
> Hello,
> 
> The attatched patch to remote.c adds support for the two commands:
> 
>         set remote read-packet-size VALUE
>         set remote write-packet-size VALUE
> 
> (and deprecates the old badly named ``set remotepacketsize''). The
> command has the following behavour:
> 
>         <=0     The default packet size (as determined
>                 by playing around with REGISTER_RAW_SIZE
>                 is restored.
> 
>         >=16k   Illegal until the alloca() are removed.
> 
>         >= ~REGISTER_RAW_SIZE/2
>                 The user is prompted for confirmation that
>                 they really really want to change the buffer
>                 size.
> 
>         other   The specified size is used but also capped
>                 by the size of the ``g'' packet returned
>                 by the target (consistent with the current
>                 behavour)!
> 
> Of course, if someone has better names (or other comments) please post
> :-)
> 
>         Andrew
> 
> (gdb) set remote read-packet-size 0
> Packet size set to the default of 400 bytes.
> (gdb) set remote read-packet-size 200
> (gdb) show remote read-packet-size
> The maximum number of characters per memory-read packet is 200.
> (gdb) set remote read-packet-size 401
> The read packet size of 401 is larger then the
> default of 400 for this target.
> Do you really want to make the change? (y or n) n
> (gdb) show remote read-packet-size
> The maximum number of characters per memory-read packet is 200.
> (gdb) set remote read-packet-size 401
> The read packet size of 401 is larger then the
> default of 400 for this target.
> Do you really want to make the change? (y or n) y
> (gdb) show remote read-packet-size
> The maximum number of characters per memory-read packet is 401.
> (gdb)
> 
>   ------------------------------------------------------------------------
> Wed Nov  3 17:14:39 1999  Andrew Cagney  <cagney@b1.cygnus.com>
> 
>         * remote.c (get_memory_packet_size, set_memory_packet_size): New
>         functions. Set/compute the size of a memory read/write packet.
>         (set_memory_read_packet_size, set_memory_write_packet_size): New.
>         Verify changes to the memory read/write packet size.
>         (memory_read_packet_size, memory_write_packet_size):
>         New. Determine the current memory read/write packet size.  A
>         function is needed as ``actual_register_packet_size'', a variable
>         is used in the calculation.
>         (register_remote_packet_sizes, build_remote_packet_sizes):
>         Initialize packet sizes according the current architecture.
>         (prefered_write_packet_size, actual_write_packet_size,
>         prefered_read_packet_size, actual_read_packet_size): New
>         variables.
>         (remote_fetch_registers, remote_fetch_registers,
>         remote_write_bytes, remote_read_bytes, build_remote_gdbarch_data):
>         Update.
>         (_initialize_remote): Add the commands ``set remote
>         read-packet-size'' and ``set remote write-packet-size''.
>         Deprecate ``set remotepacketsize''.
>