Adesto)Serial)Flash)Power)Saving)Features)and)Concepts)

Transcription

1 AdestoSerialFlashPowerSavingFeaturesandConcepts Introduction Thisnote describes and discusses unique features of Adesto Serial Flash Devices and illustrates how to implement these features to lower system>level energy consumption and increase performance. Many of these features work in conjunction with the host MCU, and through efficient software implementation, increase overall system efficiency.some of the features reduce the MCU software overheads, improving performanceandreducingmcutimewhenaccessingormanagingthememorydeviceitself,thereforedirectly reducing the energy footprint of the Host MCU. Other features reduce the energy consumption of the memorydeviceitself.lastlysomeoftheoptionsallowthesystemdesignertoimproveefficiencybyreducing thenumberofexternalcomponentsrequired,furtherreducingthesystemenergyconsumptionandimproving energyefficiency.thenetresultofthisisasystemthatrequiresfewercomponents,fewerbatteries,hasa longeroperatinglifeforagivenenergysource,andoperatesfasterwithasmallersoftwarefootprint. Whilethisnotedoesnotprovidesoftwaresolutionsorcodeexamples,itwilldiscusstheindividualmodesof operationforeachfeature,theconceptsbehindthem,andthebenefitsderivedfromtheiruse. Feature ApplicableDevices DataFlash (AT45 Fusion(AT25DF StandardSerialFlash SmallPage Erase/Write >> ActiveInterrupt >> ByteWrite >> >> UltraDeepPower DownMode >> WideOperating VoltageRange >> DualSRAMBuffers >> >> Page1of8

2 SmallPage Erase DataFlash (AT45 Fusion(AT25DF StandardSerialFlash CommandCode 0x81h 0x81h NotAvailable SmallPage Write CommandCode DataFlash (AT45 Fusion(AT25DF StandardSerialFlash 0x83h(buffer1,w/Erase 0x88h(buffer1,w/oErase 0x86h(buffer2,w/Erase 0x89h(buffer2,w/oErase 0x02h NotAvailable In the case where the application requires small packets of data to be frequently stored in non>volatile memory, or requires single bytes of data to be updated, small page Erase and Write commands improve performanceandlowerpowerusage.examplessinglebyteupdatesinclude:apincode,orlastbuttonpress, orasimpletimeanddatestamp.theseactivitiesrequirejustafewbytes tobewritten.manyindustrystandardserialflashdevicesavailabletoday allowindividualbytewriteoperations,butforcethedesignertoerasea 4KByteblockfirst.Thiscreatesinefficiencyinthesystemthatsmallpage sizesolves. Iftheblockofmemorywherethesingle>byteupdatewillbelocatedhas data that must be preserved, the MCU is required to Read the entire block into system SRAM, then erase the entire 4KByte block before updating the single>byte. This requires 4Kbytes of temporary SRAM buffer space to hold the entire 4KByte block of data while it is erased. The MCU is then required to update the single>byte in SRAM and then copy the entire 4KBytes back to the Flash. Figure 1 shows a typical software flow for this single>byte update operation when Industry StandardFlashwith4KbyteBlocksisused. NotonlyisthisinefficientbutitalsorequiresamassiveamountofMCU time, often running into 10ms to 20ms to wait for the erase cycle to Figure1 completeandthenthemcuhastomanagemultiplepageprogramcycles tore>programthedatatothespecific4kbyteblock.takingthisintoaccountthemcuisactiveforamuch Page2of8

3 longer time, consuming moreenergy, and the memory device itself is active in its programming and erase modewhichisalsoconsumingthemaximumenergy.adestofusionserialflashsolvesthisproblem. Adesto Fusion (AT25DF Serial Flash Memory supports 256Byte Page erase and 256Byte Page write capabilities. These are features added to Adesto Serial flash devices to allow designers to utilise a smaller erasegranularity,whichdirectlyreducestheactivetimeofthemcu(hostandthememorydeviceitself. SelfUcontainedReadUWriteDataBufferinginAdestoDataFlash AdestoDataFlash (AT45DBdevicessupportthepageerasecapabilityasdescribedabovebutalsoprovide additionalfeaturesthatincreaseperformanceandlowersystemenergyuse.dataflash integratestwo(2 bi>directionalsrambuffers,incontrasttoindustrystandardserialflash ssingle,unidirectionalbuffer,which canonlybeusedforprogramming.thetwin DataFlash bufferscanbeindividuallywritten> to, and read>from. These SRAM buffers can be used as temporary SRAM buffer space. Frequently updated data can be written directly to the internal SRAM buffers and, read back from these buffers, without initiating a power hungry programming or erasecycle.thereismoredetailonthistopic laterinthisnote The dual>bidirectional buffer architectural advantage of DataFlash can also be employedtoincreasetheeffectiveendurance Figure2 ofthedevice;forexamplethemcucanwrite 1,000 times to the buffer, and write once from the buffer to the flash memory array. This approach will enhancetheendurancebyafactorof1,000:1whilereducingtheprogramminganderaseenergyusedbya factorof1,000:1. Thedualbufferscanbeusedinalternatingfashiontoprovidecontinuousdatalogging.TheMCUwritesto Buffer2whileBuffer1isbeingprogrammedintotheflasharray.Similarly,Buffer2canbereadduringthis timethatthecontentsofbuffer1arebeingprogrammedintotheflasharray. Oneuseofthedualbuffersistouseonefortypicalread/writefunctions,andtheotherbufferastheholderof run>timeparameters,whichmaychangeduringoperation,butneedtobesavedateachpower>down.the Page3of8

4 bufferisusedassramuntilthepowerdownsequencegivesthecommandtowritethebuffertotheflash arrayforsafekeepinguntilthenextpor. ActiveInterrupt DataFlash (AT45 Fusion(AT25DF StandardSerialFlash CommandCode 0x25h 0x25h NotAvailable For systems that use industry standard serial flash today, when a programming or erase operation is underway,theonlywaythemcu(hostcandeterminethestatusofthedeviceistopollthememorydevice statusregister,extracttheready/busybitfromthestatusregistersequenceandmakeajudgementbasedon valuesofthepertinentbits.thisprocessistimeconsumingandmcu>resourceheavy.analternativeistolet themcusleepforsomepredeterminedlengthoftime,beforewakingupandpollingthememorydevice.this processisalittlehitormissandalsoresultsinsystemefficiencyshortfalls. Figure3 Replacethe Erasepolling loopwithan ActiveInterrupt Replacethe program/erase> pollingloopwith anactive Interrupt Adesto s patented Active Interrupt capability is implemented the Fusion (AT25DF Serial Flash memory devices, in the 2Mbit and 4Mbit densities. Active Interrupt is a command> enabled option that is used when the host initiates a program or erase operation to the serial flash. By issuing the Active Interrupt command, the MCU (the SPI bus master can then enter a sleep state during the program/erasetime.theadestomemorydevice with Active Interrupt will toggle the flash memory s SOline (which is the MCU SI line at thecompletionoftheprogram/erasecycle.the MCU SI line can be configured as an interrupt inputtowakeupthemcufromthesleepstate and continue normal operation. The Active Interruptfeaturebringsthememorydeviceinto the realm of an intelligent peripheral device, Page4of8

5 interactivelycommunicatingwiththemcuasrequiredtosignaltheendofaprogram/erasecycle. TheActiveInterruptcapabilityworksforallinternalprogrammingoperationsandallinternaleraseoperations ontheadestoserialflashmemorydevice.themcuneedstosupportedgetriggeredinterruptsonitssiline fromthememorydevice,orthesamesignalcanbetiedtoanalternativemcupinthatdoessupportinterrupt capability. This one feature will significantly reduce system energy consumption when performing programming and erase operations by allowing the MCU (host to sleep during these periods. It will reduce inefficiencies in time>outbasedsolutionsandreducesoftwarecomplexityandsize. ByteWrite CommandCode DataFlash (AT45 Fusion(AT25DF StandardSerialFlash 0x58h(buffer1 0x59h(buffer2 NotAvailable NotAvailable DataFlash (AT45DBSerialFlashdevicesoffermany features that support superior system performance and reduced software overhead. One significant feature is the inclusion of an internally managed byte write capability. Earlier in this note the page erase, and page write features were discussed. Figure4 These features allow the erase and reprogramming of smaller, more granular, blocks of data. For applications looking for single byte write and the ability to replace serial E²PROM, the DataFlash BYTEWRITEcommandisavailable.Thiscommandis availableinthedataflash E>Series(5 th Generation andlaterproducts.thebytewritecommandallows thedesignertowriteanywherefrom1bytetoafull Page of bytes, without any pre>erase or other page programming command. The device will internally manage the read>modify>write operation, providing theserialflashwiththebyte>writecapabilityusuallyfoundinseriale²promdevices.dataflash supports two bi>directional SRAM buffers, and the byte write command can be implemented through either SRAM Page5of8

6 bufferindependently.thecommand0x58haddressesbuffer1andthecommand0x59haddressesbuffer2. Ifdataiswrittentothebuffer,andthebytewritecommandisinitiated,thenonlythosemodifiedbyteswillbe writtentothememoryarray,atthedefinedpageaddress.datainun>modifiedlocationsinthatsamepage addresswillremainun>modified.thiscommandwillreducethemcusoftwareoverheadwhenwritingvery smallblocksofdata. UltraDeepPower DownMode DataFlash (AT45 Fusion(AT25DF StandardSerialFlash CommandCode 0x79h 0x79h NotAvailable Inmanyapplicationspoweredfrombatteries,coincells,orenergyharvesters,minimizingsystemenergyusage is critical. These systems also tend to spend a significant amount of their time in standby or sleep mode. Adesto memory supports this concept and Adesto serial flash memory devices implement an Ultra>Deep Power>Downmode(UDPDtoachievethelowestpowerconsumptionpossible. UDPD is an additional level of power>down capability, over and above the general standby, low power or power>downmodeanddeeppower>downmode,supportedbymostserialflasharchitecturestoday.udpdis command driven and turns off all internal memory logic, charge pumps, sense amplifiers, SRAM buffers, internal clocks and control logic, except for a simple edgetriggered,orlevel>detect,circuitonthechipselectinputpin.thiscircuitry design allows the memory to enter the lowest possible sleep state of any serial flashdevice.powerlevelsbelow150naarepossible,ascomparedtothebest>case levelsof1uaor2uatypicalofthealternativesavailableintheindustryfromother suppliestoday. Figure5 Entering the UDPD mode is accomplished by issuing the command 0x79h. If no internal programming or erase operation is underway, the device will enter the Ultra>DeepPower>Downmode.Towaketheflashmemoryup,thehostsystemsimplyneedstoactivatethe chipselectsignaltothememorydevice,andwithinashortperiodoftime,thememorydevicewillbereadyto acceptnewcommandcycles.inpractice,manyuseswillsimplysendadummycommand,ornoopcommand (acommandthathasnovalidfunctiontotheflashandbythetimeall8bitsofthedummycommandhave beenclockedin,theflashdevicewillbeawake.thelongerasystemspendsinultra>deeppower>downmode, thegreaterthebenefitthisfeaturewilldeliver. Page6of8

7 WideOperating VoltageRange ApplicableDevices DataFlash (AT45 Fusion(AT25DF StandardSerialFlash CommandCode Nocommandsrequired Nocommandsrequired NotAvailable AdestoDataFlash (AT45andFusion(AT25DFserialflashdevicesallsupportawideVCCoperatingrangeof 1.65V to 3.6V. The wide VCC range allows the memory device to operate and function directly from the battery. Many ASSP chipsets and MCU s today can operate over a wide VCC range, and are connected to various power sources including lithium chemistry based cells. In systems where serial flash memory is requiredtoprovideadditionalsystemstoragefordata,orotacapabilitythedesignerisoftenforcedtoutilize aserialflashwithlimitedvccrange(2.3vto3.6vandthenhastoaddadditionalcomponentssuchaslow Drop Out regulators, buck>boost convertors (with the additional inductors and capacitors and associated levelsshifters.thisseverelyimpactsthesystembatterylife,systemperformance,andoftenincreasesthebill of Material costs and PCB size. Wide VCC range Serial EEPROMs are available, but they are prohibitively expensiveinthedensitiesoftenrequired.adestodataflash (AT45andFusion(AT25DFserialflashdevices solvethisproblembysupportingawidevccoperatingrangeof1.65vto3.6v.somefusion(at25dfserial flash devices support 1.65V to 4.4V VCC operating range to allow direct connection to LiPoly batteries and theirassociatedchargers. Page7of8

8 BufferWrite CommandCode DataFlash (AT45 Fusion(AT25DF Phoenix(AT25SF 0x84h(buffer1 0x87h(buffer2 NotAvailable NotAvailable Figure6 AdestoDataFlash architectureintegratestwo (2 bi>directional SRAM data buffers, which are independent of each other, allowing the systemtoinitiateprogrammingviaonebuffer and to continue using the device via the 2 nd buffer.anexampleofabenefitofthisfeature is during Over>The>Air Updates (OTA, which often require programming of large areas of the array. Using both buffers, the designer can stream to buffer 2 while buffer 1 is programming, and vice versa. This will save significantamountsoftimeandenergyinthe system. Another benefit of the SRAM buffers on the DataFlash devicesistheabilitytostreamdatadirectlytothebufferandholditthereuntilwritingtotheflash arrayisrequired.thistechniquesavessignificantamountsofpreciousmcustackspaceandinternalsram resources. Finally DataFlash supports another feature that can save time and energy. If the application knows that a page is pre>erased, then the system can initiate a page program without erase. This will shorten the programmingtimetolessthan50%ofstandardflash.insystemsthatrequirepowerfailsafe,orothercritical systemdatabackup,thisshortenedpageprogrammingtimecanbeapowerfulbenefit Adesto Technologies. All rights reserved. / Rev.: ADAPP004A 2/2016 Disclaimer: Adesto Technologies Corporation makes no warranty for the use of its products, other than those expressly contained in the Company's standard warranty which is detailed in Adesto's Terms and Conditions located on the Company's web site. The Company assumes no responsibility for any errors which may appear in this document, reserves the right to change devices or specifications detailed herein at any time without notice, and does not make any commitment to update the information contained herein. No licenses to patents or other intellectual property of Adesto are granted by the Company in connection with the sale of Adesto products, expressly or by implication. Adesto's products are not authorized for use as critical components in life support devices or systems. Page8of8