memory&nbsp;architecture,&nbsp;and&nbsp;a&nbsp;large&nbsp;number&nbsp;of&nbsp;general-purpose&nbsp;registers&nbsp;and/or&nbsp;<br />register&nbsp;windows.&nbsp;The&nbsp;MIPS&nbsp;processor&nbsp;family&nbsp;is&nbsp;an&nbsp;excellent&nbsp;example.&nbsp;Contras&nbsp;<br />t&nbsp;<br />with&nbsp;CISC.&nbsp;<br />ROM&nbsp;<br />Read-Only&nbsp;Memory.&nbsp;A&nbsp;broad&nbsp;classification&nbsp;of&nbsp;memory&nbsp;devices&nbsp;that&nbsp;includes&nbsp;all&nbsp;<br />&nbsp;<br />devices&nbsp;in&nbsp;which&nbsp;the&nbsp;individual&nbsp;memory&nbsp;locations&nbsp;may&nbsp;be&nbsp;read,&nbsp;but&nbsp;not&nbsp;writte&nbsp;<br />n.&nbsp;<br />ROM&nbsp;emulator&nbsp;<br />A&nbsp;debugging&nbsp;tool&nbsp;that&nbsp;takes&nbsp;the&nbsp;place&nbsp;of-or&nbsp;emulates-the&nbsp;ROM&nbsp;on&nbsp;your&nbsp;target&nbsp;<br />board.&nbsp;A&nbsp;ROM&nbsp;emulator&nbsp;acts&nbsp;very&nbsp;much&nbsp;like&nbsp;a&nbsp;debug&nbsp;monitor,&nbsp;except&nbsp;that&nbsp;it&nbsp;<br />includes&nbsp;its&nbsp;own&nbsp;serial&nbsp;or&nbsp;network&nbsp;connection&nbsp;to&nbsp;the&nbsp;host.&nbsp;<br />ROM&nbsp;monitor&nbsp;<br />See&nbsp;debug&nbsp;monitor.&nbsp;<br />RTOS&nbsp;<br />Real-Time&nbsp;Operating&nbsp;System.&nbsp;An&nbsp;operating&nbsp;system&nbsp;designed&nbsp;specifically&nbsp;for&nbsp;us&nbsp;<br />e&nbsp;in&nbsp;<br />real-time&nbsp;systems.&nbsp;<br />race&nbsp;condition&nbsp;<br />A&nbsp;situation&nbsp;in&nbsp;which&nbsp;the&nbsp;outcome&nbsp;of&nbsp;a&nbsp;program&nbsp;may&nbsp;be&nbsp;affected&nbsp;by&nbsp;the&nbsp;exact&nbsp;o&nbsp;<br />rder&nbsp;<br />in&nbsp;which&nbsp;the&nbsp;instructions&nbsp;are&nbsp;executed.&nbsp;Race&nbsp;conditions&nbsp;are&nbsp;only&nbsp;an&nbsp;issue&nbsp;wh&nbsp;<br />ere&nbsp;<br />interrupts&nbsp;and/or&nbsp;preemption&nbsp;are&nbsp;possible&nbsp;and&nbsp;where&nbsp;critical&nbsp;sections&nbsp;exist.&nbsp;<br />&nbsp;<br />real-time&nbsp;system&nbsp;<br />Any&nbsp;computer&nbsp;system,&nbsp;embedded&nbsp;or&nbsp;otherwise,&nbsp;that&nbsp;has&nbsp;deadlines.&nbsp;The&nbsp;followin&nbsp;<br />g&nbsp;<br />question&nbsp;can&nbsp;be&nbsp;used&nbsp;to&nbsp;distinguish&nbsp;real-time&nbsp;systems&nbsp;from&nbsp;the&nbsp;rest:&nbsp;&quot;Is&nbsp;a&nbsp;l&nbsp;<br />ate&nbsp;<br />answer&nbsp;as&nbsp;bad,&nbsp;or&nbsp;even&nbsp;worse,&nbsp;than&nbsp;a&nbsp;wrong&nbsp;answer?&quot;&nbsp;In&nbsp;other&nbsp;words,&nbsp;what&nbsp;hap&nbsp;<br />pens&nbsp;<br />if&nbsp;the&nbsp;computation&nbsp;doesn't&nbsp;finish&nbsp;in&nbsp;time?&nbsp;If&nbsp;nothing&nbsp;bad&nbsp;happens,&nbsp;it's&nbsp;not&nbsp;&nbsp;<br />a&nbsp;<br />real-time&nbsp;system.&nbsp;If&nbsp;someone&nbsp;dies&nbsp;or&nbsp;the&nbsp;mission&nbsp;fails,&nbsp;it's&nbsp;generally&nbsp;consi&nbsp;<br />dered&nbsp;<br />&quot;hard&quot;&nbsp;real-time,&nbsp;which&nbsp;is&nbsp;meant&nbsp;to&nbsp;imply&nbsp;that&nbsp;the&nbsp;system&nbsp;has&nbsp;&quot;hard&quot;&nbsp;deadlin&nbsp;<br />es.&nbsp;<br />Everything&nbsp;in&nbsp;between&nbsp;is&nbsp;&quot;soft&quot;&nbsp;real-time.&nbsp;<br />recursive&nbsp;<br />Said&nbsp;of&nbsp;software&nbsp;that&nbsp;calls&nbsp;itself.&nbsp;Recursion&nbsp;should&nbsp;generally&nbsp;be&nbsp;avoided&nbsp;in&nbsp;<br />&nbsp;an&nbsp;<br />embedded&nbsp;system,&nbsp;since&nbsp;it&nbsp;frequently&nbsp;requires&nbsp;a&nbsp;large&nbsp;stack.&nbsp;<br />reentrant&nbsp;<br />Said&nbsp;of&nbsp;software&nbsp;that&nbsp;can&nbsp;be&nbsp;executed&nbsp;multiple&nbsp;times&nbsp;simultaneously.&nbsp;A&nbsp;reent&nbsp;<br />rant&nbsp;<br />function&nbsp;can&nbsp;be&nbsp;safely&nbsp;called&nbsp;recursively&nbsp;or&nbsp;from&nbsp;multiple&nbsp;tasks.&nbsp;The&nbsp;key&nbsp;to&nbsp;<br />&nbsp;making&nbsp;<br />code&nbsp;reentrant&nbsp;is&nbsp;to&nbsp;ensure&nbsp;mutual&nbsp;exclusion&nbsp;whenever&nbsp;accessing&nbsp;global&nbsp;varia&nbsp;<br />bles&nbsp;<br />or&nbsp;shared&nbsp;registers.&nbsp;<br />register&nbsp;<br />A&nbsp;memory&nbsp;location&nbsp;that&nbsp;is&nbsp;part&nbsp;of&nbsp;a&nbsp;processor&nbsp;or&nbsp;an&nbsp;I/O&nbsp;device.&nbsp;In&nbsp;other&nbsp;wor&nbsp;<br />ds,&nbsp;<br />it's&nbsp;not&nbsp;normal&nbsp;memory.&nbsp;Generally,&nbsp;each&nbsp;bit&nbsp;or&nbsp;set&nbsp;of&nbsp;bits&nbsp;within&nbsp;the&nbsp;regist&nbsp;<br />er&nbsp;<br />controls&nbsp;some&nbsp;behavior&nbsp;of&nbsp;the&nbsp;larger&nbsp;device.&nbsp;<br />relocatable&nbsp;<br />A&nbsp;file&nbsp;containing&nbsp;object&nbsp;code&nbsp;that&nbsp;is&nbsp;almost&nbsp;ready&nbsp;for&nbsp;execution&nbsp;on&nbsp;the&nbsp;targ&nbsp;<br />et.&nbsp;The&nbsp;<br />final&nbsp;step&nbsp;is&nbsp;to&nbsp;use&nbsp;a&nbsp;locator&nbsp;to&nbsp;fix&nbsp;the&nbsp;remaining&nbsp;relocatable&nbsp;addresses&nbsp;wi&nbsp;<br />thin&nbsp;the&nbsp;<br />code.&nbsp;The&nbsp;result&nbsp;of&nbsp;that&nbsp;process&nbsp;is&nbsp;an&nbsp;executable.&nbsp;<br />reset&nbsp;address&nbsp;<br />The&nbsp;address&nbsp;from&nbsp;which&nbsp;the&nbsp;first&nbsp;instruction&nbsp;will&nbsp;be&nbsp;fetched&nbsp;after&nbsp;the&nbsp;proce&nbsp;<br />ssor&nbsp;<br />is&nbsp;powered&nbsp;on&nbsp;or&nbsp;reset.&nbsp;<br />reset&nbsp;code&nbsp;<br />A&nbsp;small&nbsp;piece&nbsp;of&nbsp;code&nbsp;that&nbsp;is&nbsp;placed&nbsp;at&nbsp;the&nbsp;reset&nbsp;address.&nbsp;The&nbsp;reset&nbsp;code&nbsp;is&nbsp;<br />&nbsp;usually&nbsp;<br />written&nbsp;in&nbsp;assembly&nbsp;language&nbsp;and&nbsp;may&nbsp;simply&nbsp;be&nbsp;the&nbsp;equivalent&nbsp;of&nbsp;&quot;jump&nbsp;to&nbsp;th&nbsp;<br />e&nbsp;<br />startup&nbsp;code.&quot;&nbsp;<br />reset&nbsp;vector&nbsp;<br />See&nbsp;reset&nbsp;address.&nbsp;<br />S&nbsp;<br />SRAM&nbsp;<br />Static&nbsp;Random-Access&nbsp;Memory.&nbsp;A&nbsp;type&nbsp;of&nbsp;RAM&nbsp;that&nbsp;retains&nbsp;its&nbsp;contents&nbsp;as&nbsp;long&nbsp;<br />&nbsp;as&nbsp;<br />the&nbsp;system&nbsp;is&nbsp;powered&nbsp;on.&nbsp;Data&nbsp;stored&nbsp;in&nbsp;an&nbsp;SRAM&nbsp;is&nbsp;lost&nbsp;when&nbsp;the&nbsp;system&nbsp;is&nbsp;<br />powered&nbsp;down&nbsp;or&nbsp;reset.&nbsp;<br />scheduler&nbsp;<br />The&nbsp;part&nbsp;of&nbsp;an&nbsp;operating&nbsp;system&nbsp;that&nbsp;decides&nbsp;which&nbsp;task&nbsp;to&nbsp;run&nbsp;next.&nbsp;This&nbsp;de&nbsp;<br />cision&nbsp;<br />is&nbsp;based&nbsp;on&nbsp;the&nbsp;readiness&nbsp;of&nbsp;each&nbsp;task,&nbsp;their&nbsp;relative&nbsp;priorities,&nbsp;and&nbsp;the&nbsp;s&nbsp;<br />pecific&nbsp;<br />scheduling&nbsp;algorithm&nbsp;implemented.&nbsp;<br />semaphore&nbsp;<br />A&nbsp;data&nbsp;structure&nbsp;that&nbsp;is&nbsp;used&nbsp;for&nbsp;intertask&nbsp;synchronization.&nbsp;Semaphores&nbsp;are&nbsp;<br />usually&nbsp;provided&nbsp;by&nbsp;the&nbsp;operating&nbsp;system.&nbsp;<br />simulator&nbsp;<br />A&nbsp;debugging&nbsp;tool&nbsp;that&nbsp;runs&nbsp;on&nbsp;the&nbsp;host&nbsp;and&nbsp;pretends&nbsp;to&nbsp;be&nbsp;the&nbsp;target&nbsp;process&nbsp;<br />or.&nbsp;A&nbsp;<br />simulator&nbsp;can&nbsp;be&nbsp;used&nbsp;to&nbsp;test&nbsp;pieces&nbsp;of&nbsp;the&nbsp;software&nbsp;before&nbsp;the&nbsp;embedded&nbsp;<br />hardware&nbsp;is&nbsp;available.&nbsp;Unfortunately,&nbsp;attempts&nbsp;to&nbsp;simulate&nbsp;interactions&nbsp;with&nbsp;<br />&nbsp;<br />complex&nbsp;peripherals&nbsp;are&nbsp;often&nbsp;more&nbsp;trouble&nbsp;than&nbsp;they&nbsp;are&nbsp;worth.&nbsp;<br />software&nbsp;interrupt&nbsp;<br />An&nbsp;interruption&nbsp;of&nbsp;a&nbsp;program&nbsp;that&nbsp;is&nbsp;initiated&nbsp;by&nbsp;a&nbsp;software&nbsp;instruction.&nbsp;So&nbsp;<br />ftware&nbsp;<br />interrupts&nbsp;are&nbsp;commonly&nbsp;used&nbsp;to&nbsp;implement&nbsp;breakpoints&nbsp;and&nbsp;operating&nbsp;system&nbsp;<br />entry&nbsp;points.&nbsp;Unlike&nbsp;true&nbsp;interrupts,&nbsp;they&nbsp;occur&nbsp;synchronously&nbsp;with&nbsp;respect&nbsp;&nbsp;<br />to&nbsp;<br />program&nbsp;execution.&nbsp;In&nbsp;other&nbsp;words,&nbsp;software&nbsp;interrupts&nbsp;always&nbsp;occur&nbsp;at&nbsp;the&nbsp;<br />beginning&nbsp;of&nbsp;an&nbsp;instruction&nbsp;execution&nbsp;cycle.&nbsp;Compare&nbsp;with&nbsp;trap.&nbsp;<br />stack&nbsp;<br />An&nbsp;area&nbsp;of&nbsp;memory&nbsp;that&nbsp;contains&nbsp;a&nbsp;last-in-first-out&nbsp;queue&nbsp;of&nbsp;storage&nbsp;for&nbsp;<br />parameters,&nbsp;automatic&nbsp;variables,&nbsp;return&nbsp;addresses,&nbsp;and&nbsp;other&nbsp;information&nbsp;tha&nbsp;<br />t&nbsp;<br />must&nbsp;be&nbsp;maintained&nbsp;across&nbsp;function&nbsp;calls.&nbsp;In&nbsp;multitasking&nbsp;situations,&nbsp;each&nbsp;t&nbsp;<br />ask&nbsp;<br />generally&nbsp;has&nbsp;its&nbsp;own&nbsp;stack.&nbsp;<br />stack&nbsp;frame&nbsp;<br />An&nbsp;area&nbsp;of&nbsp;the&nbsp;stack&nbsp;associated&nbsp;with&nbsp;a&nbsp;particular&nbsp;function&nbsp;call.&nbsp;<br />startup&nbsp;code&nbsp;<br />A&nbsp;piece&nbsp;of&nbsp;assembly&nbsp;language&nbsp;code&nbsp;that&nbsp;prepares&nbsp;the&nbsp;way&nbsp;for&nbsp;software&nbsp;written&nbsp;<br />&nbsp;in&nbsp;a&nbsp;<br />high-level&nbsp;language.&nbsp;Most&nbsp;C/C++&nbsp;cross-compilers&nbsp;come&nbsp;with&nbsp;startup&nbsp;code&nbsp;that&nbsp;&nbsp;<br />you&nbsp;<br />can&nbsp;modify,&nbsp;compile,&nbsp;and&nbsp;link&nbsp;with&nbsp;your&nbsp;embedded&nbsp;programs.&nbsp;<br />T&nbsp;<br />target&nbsp;<br />Another&nbsp;name&nbsp;for&nbsp;the&nbsp;embedded&nbsp;system.&nbsp;This&nbsp;term&nbsp;is&nbsp;usually&nbsp;used&nbsp;during&nbsp;softw&nbsp;<br />are&nbsp;<br />development,&nbsp;to&nbsp;distinguish&nbsp;the&nbsp;embedded&nbsp;system&nbsp;from&nbsp;the&nbsp;host&nbsp;with&nbsp;which&nbsp;it&nbsp;<br />communicates.&nbsp;<br />task&nbsp;<br />The&nbsp;central&nbsp;abstraction&nbsp;of&nbsp;an&nbsp;operating&nbsp;system.&nbsp;Each&nbsp;task&nbsp;must&nbsp;maintain&nbsp;its&nbsp;&nbsp;<br />own&nbsp;<br />copy&nbsp;of&nbsp;the&nbsp;instruction&nbsp;pointer&nbsp;and&nbsp;general-purpose&nbsp;registers.&nbsp;Unlike&nbsp;proces&nbsp;<br />ses,&nbsp;<br />tasks&nbsp;share&nbsp;a&nbsp;common&nbsp;memory&nbsp;space&nbsp;and&nbsp;must&nbsp;be&nbsp;careful&nbsp;to&nbsp;avoid&nbsp;overwriting&nbsp;e&nbsp;<br />ach&nbsp;<br />other's&nbsp;code&nbsp;and&nbsp;data.&nbsp;<br />thread&nbsp;<br />Another&nbsp;name&nbsp;for&nbsp;a&nbsp;task.&nbsp;This&nbsp;name&nbsp;is&nbsp;more&nbsp;common&nbsp;in&nbsp;operating&nbsp;systems&nbsp;that&nbsp;<br />support&nbsp;processes.&nbsp;A&nbsp;task&nbsp;is&nbsp;simply&nbsp;a&nbsp;thread&nbsp;in&nbsp;a&nbsp;single-process&nbsp;system.&nbsp;<br />tracepoint&nbsp;<br />Like&nbsp;a&nbsp;breakpoint&nbsp;except&nbsp;that&nbsp;a&nbsp;counter&nbsp;is&nbsp;incremented&nbsp;rather&nbsp;than&nbsp;stopping&nbsp;&nbsp;<br />the&nbsp;<br />program.&nbsp;Tracepoints&nbsp;are&nbsp;not&nbsp;supported&nbsp;by&nbsp;all&nbsp;debugging&nbsp;tools.&nbsp;<br />trap&nbsp;<br />An&nbsp;interruption&nbsp;of&nbsp;a&nbsp;program&nbsp;that&nbsp;is&nbsp;triggered&nbsp;by&nbsp;the&nbsp;processor's&nbsp;own&nbsp;intern&nbsp;<br />al&nbsp;<br />hardware.&nbsp;For&nbsp;example,&nbsp;the&nbsp;processor&nbsp;might&nbsp;trap&nbsp;if&nbsp;an&nbsp;illegal&nbsp;opcode&nbsp;is&nbsp;foun&nbsp;<br />d&nbsp;<br />within&nbsp;the&nbsp;program.&nbsp;Compare&nbsp;with&nbsp;software&nbsp;interrupt.&nbsp;<br />V&nbsp;<br />volatile&nbsp;<br />A&nbsp;value&nbsp;that&nbsp;may&nbsp;change&nbsp;without&nbsp;the&nbsp;intervention&nbsp;of&nbsp;software&nbsp;is&nbsp;said&nbsp;to&nbsp;be&nbsp;v&nbsp;<br />olatile.&nbsp;<br />For&nbsp;example,&nbsp;values&nbsp;within&nbsp;the&nbsp;registers&nbsp;of&nbsp;some&nbsp;I/O&nbsp;devices&nbsp;may&nbsp;change&nbsp;in&nbsp;<br />response&nbsp;to&nbsp;external&nbsp;events.&nbsp;C's&nbsp;volatile&nbsp;keyword&nbsp;should&nbsp;be&nbsp;used&nbsp;to&nbsp;warn&nbsp;you&nbsp;<br />r&nbsp;<br />compiler&nbsp;about&nbsp;any&nbsp;pointers&nbsp;that&nbsp;point&nbsp;to&nbsp;such&nbsp;registers.&nbsp;This&nbsp;will&nbsp;ensure&nbsp;t&nbsp;<br />hat&nbsp;the&nbsp;<br />actual&nbsp;value&nbsp;is&nbsp;reread&nbsp;each&nbsp;time&nbsp;the&nbsp;data&nbsp;is&nbsp;used.&nbsp;<br />W&nbsp;<br />watchdog&nbsp;timer&nbsp;<br />A&nbsp;hardware&nbsp;timer&nbsp;that&nbsp;is&nbsp;periodically&nbsp;reset&nbsp;by&nbsp;software.&nbsp;If&nbsp;the&nbsp;software&nbsp;cra&nbsp;<br />shes&nbsp;<br />or&nbsp;hangs,&nbsp;the&nbsp;watchdog&nbsp;timer&nbsp;will&nbsp;expire,&nbsp;and&nbsp;the&nbsp;entire&nbsp;system&nbsp;will&nbsp;be&nbsp;rese&nbsp;<br />t&nbsp;<br />automatically.&nbsp;<br />&nbsp;<br 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