Accessing System Resources in Java

Creation Denso QR Bar Code in Java Accessing System Resources
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Accessing System Resources
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Systemoutprintln("Shiny new date: " + new Date()); } catch (IOException ioe) { ioeprintStackTrace(); } finally { try { sclose(); } catch (IOException e) {} } } }
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SetClock takes the host name (wally, in this case) or IP address of the time server from the command line It connects to the speci ed host and reads the 32bit time value using the readInt method on a javaioDataInputStream object There is one somewhat subtle point here Since the int primitive type is signed, the result returned from readInt must be promoted to a long and then truncated using the mask 0xFFFFFFFFL This choice of a mask results in both the promotion of the value returned from readInt as well as removing the effect of the unwanted sign extension The result is the true, unsigned 32-bit value returned by the time server represented within a long Since longs are 64 bits in width, this leaves plenty of room to perform the nal multiplication without the possibility of over ow Note that we could solve the problem more directly using the readLong method of DataInputStream The time server returns only 4 bytes before closing the connection The readLong method would attempt to read 8 bytes, and this would result in a javaioIOException being thrown by the underlying socket It is easier to see the effect of this example by rst setting a bogus date and time using the slush date command before running SetClock
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TINI /> date 010120250000 GMT TINI /> date Wed Jan 1 00:00:22 GMT 2025 TINI /> java SetClocktini wally Crusty date: Wed Jan 01 00:01:06 GMT 2025 Shiny new date: Wed Jan 31 16:33:09 CST 2001
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SetClock uses the Date class to display the date and time before and after setting the RTC using setTickCount Just for good measure, it also sets the local time zone before displaying the new date and time Finally, note that setting the clock is not something that an application must perform every time it is run The clock is powered by a small lithium cell so that accurate time is maintained even in the absence of main power (V cc) However, some applications may want to use a network time server to synchronize the clock with the network time during the initialization phase and perhaps periodically thereafter
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The Watchdog
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THE WATCHDOG
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The watchdog timer provides a hardware reset of TINI s microcontroller to recover from fatal problems in software that prevent normal operation of the embedded system as a whole This section presents the need for a watchdog and describes its use from a Java application
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Motivation for Using the Watchdog
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Many embedded systems are deployed in remote locations and must run continuously without manual intervention To achieve very reliable operation over long periods of time, an embedded system needs a mechanism for detecting and correcting fatal execution errors in the software that controls the system Unresponsive software can be caused by several distinct problems such as the following Thread termination due to an unhandled exception Deadlocked threads A crash of the underlying OS Momentary hardware failures due to environmental stresses such as ESD (Electrostatic Discharge)
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Of course application software should be written and tested to avoid these problems to the largest extent possible However, for large applications executing under complex operating environments, like TINI, it is very dif cult to guarantee awless operation under all conditions Also, there is no way for application or system-level software to guard against things like processor glitches, possibly caused by environmental stresses, that usually result in runaway code Whatever mechanism we use to protect against hanging applications, it can t be a purely software-based solution, since unreliable software operation is exactly what we re trying to protect against in the rst place The system software must be protected by a simple and reliable underlying hardware construct For this reason, TINI s microcontroller supports a hardware-based timer known as the watchdog The purpose of the watchdog is to guard against runaway code The watchdog timer can be thought of as a countdown to a hard reset If the timer ever expires, it produces an effect that is roughly equivalent to hitting the reset button on your PC Using the watchdog timer is a harsh but effective way to ensure that your application does not hang inde nitely, leaving the system in an unresponsive and useless state The basic idea behind the operation of the watchdog is that periodically in your code you reinitialize or feed the watchdog, preventing a reset If the code has become unresponsive to the point that it can t execute the critical sections of
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