Controlling MSP with Messages
You can control MSP using the message box object. Normally, the message box contains an object, and you click on it or replace a variable typed into the message box to send a message via a patch cord to another Max object. However, if the message in a message box begins with a semicolon (;) followed by the word dsp, any message which follows will be sent directly to the Max application itself, just as though there were a receive object named "dsp".

Sending a message to the Max application
When you click on the message box or send it a bang or a value, the message will be sent to the Max application.

Here is listing of the messages you can send to the Max application using this technique:
cpulimit
The word cpulimit, followed by a number in the range 0-100, sets a utilization limit for the CPU. Above this limit, MSP will not process audio vectors until the utilization comes back down, causing a click. If the cpu limit is set to either 0 or 100, there will be no limit checking done.
inremap
The word inremap, followed by two numbers that specify a physical device input channel number and a logical input channel number, maps the physical device to the logical input channel.
iovs
The word iovs, followed by a number that is a power of 2, sets the I/O vector size.
open
The word open opens the DSP Status window.
optimize
The word optimize, followed by a zero or one, turns Altivec optimization on (1) or off (0).
outremap
The word outremap, followed by two numbers that specify a logical device output channel number and a physical output channel number, maps the logical device to the physical output channel.
set
The word set, followed by a zero or one, turns the audio on (1) or off (0). It is equivalent to clicking on a ezadc~ or ezdac~ object.
setdriver
The word setdriver, followed by a number, sets a new audio driver based on its index into the currently generated menu of drivers created by the adstatus driver object. If the word setdriver is followed by a symbol that names a valid driver, the new driver is selected by name. An additional symbol argument may be used to specify a "subdriver" (e.g., ASIO drivers use ASIO as the name of the driver and PCI-324 as a subdriver name that specifies a specific device).
sigvs
The word sigvs, followed by a number that is a power of 2, sets the I/O signal vector size.
sr
The word sr, followed by a number, sets a new sampling rate In Hertz.
start
The word start turns the audio on.
status
The word status opens the DSP Status window.
stop
The word stop turns the audio off.
takeover
The word takeover, followed by a zero or one, turns Scheduler in Audio Interrupt mode on (1) or off (0). It is equivalent to clicking on the Scheduler in Overdrive checkbox in the DSP Status window.
timecode
The word timecode followed by a zero or one, starts (1) or stops (0) timecode reading by any audio drivers that support the feature (ASIO 2).
wclose
The word wclose closes the DSP Status window.