描述
3HAC023195-001
技巧1——用已知值填充ROM
軟件開(kāi)發(fā)人員往往都是非常樂(lè)觀(guān)的一群人,只要讓他們的代碼忠實(shí)地長(zhǎng)時(shí)間地運(yùn)行就可以了,僅此而已。微控制器跳出應(yīng)用程序空間并在非預(yù)想的代碼空間中執(zhí)行這種情況似乎是相當(dāng)少有的。然而,這種情況發(fā)生的機(jī)會(huì)并不比緩存溢出或錯(cuò)誤指針失去引用少。它確實(shí)會(huì)發(fā)生!發(fā)生這種情況后的系統(tǒng)行為將是不確定的,因?yàn)槟J(rèn)情況下內(nèi)存空間都是0FF,或者由于內(nèi)存區(qū)通常沒(méi)有寫(xiě)過(guò),其中的值可能只有上帝才知道。
不過(guò)有相當(dāng)完備的linker或IDE技巧可以用來(lái)幫助識(shí)別這樣的事件并從中恢復(fù)系統(tǒng)。技巧就是使用FILL命令對(duì)未用ROM填充已知的位模式。要填充未使用的內(nèi)存,有很多不同的可能組合可以使用,但如果是想建立更加可靠的系統(tǒng),最明顯的選擇是在這些位置放置ISR fault handler。如果系統(tǒng)出了某些差錯(cuò),處理器開(kāi)始執(zhí)行程序空間以外的代碼,就會(huì)觸發(fā)ISR,并在決定校正行動(dòng)之前提供儲(chǔ)存處理器、寄存器和系統(tǒng)狀態(tài)的機(jī)會(huì)。
技巧2——檢查應(yīng)用程序的CRC
對(duì)嵌入式工程師來(lái)說(shuō)一個(gè)很大的好處是,我們的IDE和工具鏈可以自動(dòng)產(chǎn)生應(yīng)用程序或內(nèi)存空間校驗(yàn)和(Checksum),從而根據(jù)這個(gè)校驗(yàn)和驗(yàn)證應(yīng)用程序是否完好。有趣的是,在許多這些案例中,只有在將程序代碼加載到設(shè)備時(shí),才會(huì)用到校驗(yàn)和。
然而,如果CRC或校驗(yàn)和保持在內(nèi)存中,那么驗(yàn)證應(yīng)用程序在啟動(dòng)時(shí)(或甚至對(duì)長(zhǎng)時(shí)間運(yùn)行的系統(tǒng)定期驗(yàn)證)是否仍然完好是確保意外之事不會(huì)發(fā)生的極好途徑?,F(xiàn)在一個(gè)編程過(guò)的應(yīng)用程序發(fā)生改變的概率是很小的,但考慮每年交付的數(shù)十億個(gè)微控制器以及可能惡劣的工作環(huán)境,應(yīng)用程序崩潰的機(jī)會(huì)并不是零。更有可能的是,系統(tǒng)中的一個(gè)缺陷可能導(dǎo)致某一扇區(qū)發(fā)生閃存寫(xiě)入或閃存擦除,從而破壞應(yīng)用程序的完整性。
產(chǎn)品承諾:
保?證?全新原裝進(jìn)口,
保?證?安全準(zhǔn)時(shí)發(fā)貨,
保?證售后服務(wù)質(zhì)量,
優(yōu)勢(shì)價(jià)格,大量現(xiàn)貨。
主營(yíng)DCS系統(tǒng)配件
機(jī)器人系統(tǒng)配件
大型伺服系統(tǒng)配件
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