Abstract:
A secure mechanism for remotely controlling the power-on state of a host computer: A microcontroller in the host computer is supplied with standby power even when system power to the host computer is turned off. The microcontroller senses the state of the host computer&#39;s RS-232 receive line so that commands may be sent to the microcontroller over an RS-232 connection to the host computer. An output of the microcontroller is logically ORed with the output of a power switch debounce circuit of the host computer. The output of the logical OR function is used to manipulate the power-on state of the host computer. The microcontroller may be programmed to respond to numerous commands.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to the remote control of computer systems. More particularly, the invention relates to techniques for remotely controlling the power-on and power-off states of individual computers. 
     BACKGROUND 
     Multiple individual computers are frequently ganged together for commercial uses of various kinds. For example, network “server farms” commonly include numerous racks of individual computers, each rack populated by several rack-mounted network server computers. In such an environment, it is desirable for a system administrator to be able to control certain functions and states of the individual computers remotely. In particular, it is desirable for a system administrator to be able to remotely control whether an individual computer is powered-on or powered-off. 
     One prior art method that has been employed to remotely control the power-on state of individual computers has been to use a local area network (“LAN”) connection. For example, a multiaccess computing (“MAC”) address can be used to select an individual machine using a LAN and to cause the machine to power itself on when its MAC address is detected. Solutions according to this scheme are sometimes referred to as “wake on LAN” solutions. Unfortunately, such solutions lack flexibility: The simple ability to power a machine on remotely is not as useful as the ability to turn it on and off, and to be able to specify the manner in which the machine turns off. (For example, it is sometimes desirable to specify a “soft” power down wherein the machine ends running processes in a controlled manner. At other times, it is desirable to specify a “hard” power down wherein the machine simply stops immediately.) Although other MAC address/LAN techniques have been employed having greater flexibility and features, these more elaborate solutions typically require more than one MAC or IP address per machine. The use of multiple addresses results in significantly higher implementation cost and complexity. 
     Moreover, MAC address/LAN techniques lack security: Almost by definition, the use of a LAN means that multiple users will have access to the individual machines that are connected to the LAN. In such an environment, the MAC addresses for the individual machines will be readily available to users. Therefore, it would be possible for the power-on state of an individual machine to be altered either by mistake or maliciously; either possibility is undesirable. 
     It is therefore an object of the invention to provide a flexible and secure mechanism for controlling the power-on state of individual computers remotely. 
     SUMMARY OF THE INVENTION 
     These and other objects are realized by a secure mechanism for remotely controlling the power-on state of a computer. 
     In one aspect, a microcontroller is added to the computer that will be remotely controlled. The microcontroller is supplied with power via a standby power supply even when power to the host computer is turned off. The microcontroller senses the state of the host computer&#39;s RS-232 receive line so that commands may be sent to the microcontroller over an RS-232 connection to the host computer. An output of the microcontroller is logically ORed with the output of a power switch debounce circuit of the host computer. The output of the logical OR function is used to control the power-on state of the host computer. 
     In another aspect, the microcontroller may be programmed to respond to numerous commands related to the power-on state of the host computer. For example, a first command may be used to turn the host computer on immediately. A second command may be used to turn the host computer off immediately. A third command may be used to cause the host computer to execute a “soft” power down wherein all processes are exited prior to turning off power. And a fourth command may be used to place the microcontroller in a sleep mode. Numerous other command features are possible. 
     In still another aspect, multiple such host computers may be coupled to a system console using independent RS-232 connections. In this manner, a system administrator may remotely control the power-on state of each host computer individually. 
     The remote control mechanism of the invention provides flexibility because many different command sequences may be transmitted over the RS-232 connections. The mechanism is secure because each host computer&#39;s power-on state is controlled using an independent RS-232 connection rather than by using the LAN; RS-232 connections are not easily accessed by unauthorized users. Moreover, the mechanism is inexpensive because it utilizes RS-232 hardware rather than more expensive LAN hardware. The mechanism may be used to control a single computer or may be scaled to control a large set of computers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a system console coupled to multiple remote computers with independent RS-232 connections according to a preferred embodiment of the invention. 
         FIG. 2  is a block diagram illustrating a representative one of the multiple remote computers of  FIG. 1 . 
         FIG. 3  is a schematic diagram illustrating the resistor/diode level shifter of  FIG. 2  in more detail. 
         FIG. 4  is a state diagram illustrating preferred behavior for the microcontroller of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Structure. Preferred structure for implementing the invention will now be described with reference to  FIGS. 1–3 . 
       FIG. 1  illustrates a system console  100  coupled to multiple remote computers  102 – 110  with independent RS-232 connections  112  according to a preferred embodiment of the invention. One RS-232 connection is provided for each of the remote computers to be controlled from console  100 . Prior art software may be executed on console  100  making the console operable to issue user-typed commands to the remote computers independently over the appropriate RS-232 connections. 
       FIG. 2  illustrates a representative one of the multiple remote computers of  FIG. 1 . Computer  200  has an RS-232 port terminated at serial connector  202 . Computer  200  also has a power switch  204  coupled to a power switch debounce circuit  206 . Debounce circuit  206  presents a debounced output signal  208  to one of the inputs of OR gate  210 . The output of OR gate  210  constitutes a power control signal  212  which is used to manipulate the power-on state of computer  200  in a manner to described in more detail below. The other input of OR gate  210  is provided by a power control output  214  of microcontroller  216 . Using this arrangement, power control signal  212  may be asserted either by power switch debounce circuit  206  or by microcontroller  216 . 
     Microcontroller  216  is supplied with continuous standby power  218  via power supply  220  even when system power to host computer electronics  222  is turned off. Microcontroller  216  senses the state of RS-232 receive line  224  via TTL RX input  226 . (TTL RX input  226  follows the state of RS-232 receive line  224 , but is clamped to TTL logic levels by resistor/diode level shifter  228 .) Microcontroller  216  also has an input coupled to host computer system power  230 , and another input coupled to remote power enable (RP EN) signal  232 . Preferably, the state of system power input  230  should reflect whether the host computer power is on or off. The state of RP EN input  232  should reflect the state of a firmware enable bit within host computer electronics  222 . Such a firmware enable bit may be allocated by conventional means, and may be set/reset during boot-up of computer  200  also by conventional means. 
       FIG. 3  is a schematic diagram illustrating the resistor/diode level shifter of  FIG. 2  in more detail. The level shifter may simply constitute a series resistor  300  and a pair of diodes  302 ,  304  configured as shown. The circuit is operable to clamp a high  10 . RS-232 voltage to the standby power voltage, and to clamp a low RS-232 voltage to ground. Other suitable level shifters may be used. Alternatively, a microcontroller may be used that has the ability to accept RS-232 voltage levels on its inputs. 
     Operation. Preferred operation of the invention will now be described with reference to the state diagram of  FIG. 4 . 
     Initialization. On standby power-up or reset, software running on microcontroller  216  initializes to state A and sets an internal “microcontroller on” (MCON) state bit to 1. When RP EN is determined to be valid (not tristated or indeterminate) and 0, software transitions to states B through F, wherein the RS-232 baud rate is automatically detected and characters are clocked into a receive buffer. NOTE: RP EN is not valid when system power to the host computer is not turned on. In an embodiment, the microcontroller was programmed to transition to state B regardless of the state of the RP EN bit when standby power was first turned on; this allowed the remote power-on functionality to be available upon reset even though system power had not yet been turned on. Thereafter, the state of the MCON bit was checked every time state A was entered; thus the MCON bit effectively “remembered” the state of the RP EN bit of the host computer. 
     Auto Baud Rate Detect and Character Receipt. In state B, a receive buffer is cleared, a variable numChars is set to 0, and a variable cmdMode is set to 0. Software then transitions to state C. Once in state C, the state of the TTL RX input is monitored. As soon as TTL RX goes high, a timer or counter is initiated and software transitions to state D. In state D, TTL RX is again monitored. As soon as TTL RX goes low, the timer or counter will be stopped and software transitions to state E. 
     The software is designed to assume that, once state E has been reached, the value of the timer or counter will reflect the duration of a start bit. Thus, in state E, the baud rate is set according to the value of the timer or counter. Preferably, the user  1  should enter carriage returns (&lt;CR&gt;) at console  100  in order to establish the baud rate, as the &lt;CR&gt; character guarantees a start bit of 1 followed immediately by a 0. While in state E, and after the baud rate has been set, software clocks one character following the start bit into the receive buffer. If the received character was a &lt;CR&gt;, then software will continue looping in state E and will set the baud rate again. (Alternatively, the software may transition from state E to states A, B or C to re-determine the baud rate.) But if the character was anything other than &lt;CR&gt;, software will set the variable cmdMode to 1 and transition to state F. 
     In state F, software places the just-received character into the receive buffer and increments the numChars variable. Software will remain in state F clocking additional characters into the receive buffer and incrementing numChars until either numChars exceeds 11 characters or until a &lt;CR&gt; is encountered. If the terminating condition was numChars&gt;11, software resets to state A. But if the terminating condition was a &lt;CR&gt;, then software transitions to state G. 
     Once in state G, software checks the state of the RP EN bit to determine whether remote power-on functionality has been disabled. If the RP EN bit is 1 (indicating a disable condition), then software will transition to state H. In state H, the MCON state variable is reset to 0, and software resets to state A. On the other hand, if RP EN is 0 (indicating an enable condition), software transitions to state I, wherein the just-received command will be interpreted. 
     Command Processing. In state I, software examines the contents of the receive buffer and acts accordingly: If the contents indicate an illegal, unrecognized, or “no command,” software resets to state A. But if the contents indicate one of a predetermined number of recognized commands, software will transition to a state determined by the command as follows. 
     On Command: If the buffer contents indicate an “on” command, software transitions from state I to state J. In state J, the value of system power line  230  (sysState) is tested to determine the current power-on state of the host computer. If sysState is 1, then the host computer is powered on already an no action is necessary. Therefore, software resets to state A. But if sysState is 0, then software transitions to state K. In state K, microcontroller  214  asserts power control output  214  for a predetermined time and then unasserts the signal. The state of power control input  212  will follow the pulse applied to output  214  and will cause system power to be turned on. The duration of the necessary pulse on power control input  212  will vary with the characteristics of host computer electronics  222 . After asserting output  214  for the necessary interval, software resets to state A. 
     Off Command: If the buffer contents indicate an “off” command, software transitions from state I to state L. In state L, the value of system power line  230  (sysState) is tested to determine the current power-on state of the host computer. If sysState is 0, then the host computer is powered off already an no action is necessary. Therefore, software resets to state A. But if sysState is 1, then software transitions to state K. In state K, microcontroller  214  asserts power control output  214  for a predetermined time and then unasserts the signal. The state of power control input  212  will follow the pulse applied to output  214  and will cause system power to be turned off. The duration of the necessary pulse on power control input  212  will vary with the characteristics of host computer electronics  222 . After asserting output  214  for the necessary interval, software resets to state A. 
     OffNow Command: If the buffer contents indicate an “OffNow” command, software transitions from state I to state M. In state M, the value of system power line  230  (sysState) is tested to determine the current power-on state of the host computer. If sysState is 0, then the host computer is powered off already an no action is necessary. Therefore, software resets to state A. But if sysState is 1, then software transitions to state N. In state N, microcontroller  214  asserts power control output  214  for a longer predetermined time and then unasserts the signal. Preferably, host computer electronics  222  will interpret the longer pulse on power control input  212  to mean that system power should be turned off immediately, without waiting for all processes to be terminated in a controlled manner. The state of power control input  212  will follow the pulse applied to output  214  and will cause system power to be turned off. The duration of the necessary pulse on power control input  212  will vary with the characteristics of host computer electronics  222 . After asserting output  214  for the necessary interval, software resets to state A. 
     Sleep Command: Preferably, it should be possible to disable the above-described remote power-on functionality in a selected host computer by issuing a “sleep” command from console  100 . The result of the sleep command should be to cause the selected host computer to cease interpreting RS-232 inputs as possible power-on or power-off commands. Thus, if the buffer contents indicate a “sleep” command, software transitions from state I to state O. In state O, software will perpetually loop until the state of RP EN is sensed to be 1 (indicating a disable condition). Once this occurs, software will transition to state P where it will perpetually loop until the state of RP EN is sensed to be 0 (indicating an enable condition). Once this occurs, software will reset to state A. While in either of states O or P, software will not be responding to new inputs on RS-232 receive line  224 ; thus, the remote power-on functionality will effectively be sleeping. But if the user desires to restore remote power-on functionality, he may do so by setting and then resetting the state of the RP EN bit (such as by rebooting the host computer to access its firmware configuration). 
     While the invention has been described in detail in relation to a preferred embodiment thereof, the described embodiment has been presented by way of example and not by way of limitation. It will be understood by those skilled in the art that various changes may be made in the form and details of the described embodiment without deviating from the spirit and scope of the invention as defined by the appended claims.