okay this is a introductory programmingclass this is technical stuff andhopefully it will inspire some peoplewho may not have ever tried to write adevice driver to maybe actually try itif they have something they wantsupported or or whatever just for funokay let's talk a little bit about theway device driver is laid outessentially you have two segments ofmemory a data segment in a code segmentand a requirement of a device driver asif there's a header at the beginning ofyour data segment and this headercontains information that informs thekernel how to access your driverthere's pointers into a strategy routineand that is how the driver talks to howthe colonel talks to your driver a32-bit driver will actually have anothersegment of 32-bit code segments inaddition to the two segments that a16-bit driver has the data segment alsohas the header the same that header hasto be there because the kernel expectsit to be there and this is not the onlyway to build a 32-bit driver this isjust how I have done it because thismakes things very easy okayany questions feel free to ask questionsI'm gonna kind of move along because I'mgonna get to an actual writing a devicedriver in real life with real time okaymoving on the main thing that yourdriver needs to have for communicationwith the kernel is the strategy handlerthe first time so when your driver getsloaded via a device statement or a basethat statement in your in your configdot sis the first thing that drive theColonel will do is load your driver intomemory set up the device header it'llread the the address out of the deviceheader so it knows what function to callto initialize your driver and it alsowill write the code segment and datasegment selectors into that header sothe first thing the kernel does is itcalls that strategy handler with an initfunction and that allows your driver todo whatever it needs to do to initializeitself then later on after all of thedrivers are loaded the driver the kernelwill call your driver again with afunction called an it complete at thispoint you're guaranteed that all theother drivers are loaded and this is thetime you would do things like connect toother drivers for inter drivercommunication for example if one driverneeds to talk to another driver this iswhen they would connect to each otherthe USB drivers do that a lot they do alot of talking between the differentdrivers via this inter drivercommunication mechanism there are otherfunctions that the strategy Handler canimplement such as open closed readwritesave restore shut down various thingsthe open closed and read and write areexactly mapped to when you would do aopen a file open in a program and a fileread and a flow right and that's thekind of example I'm going to show youtoday to make writing device driverseasy I've developed these two kits and Imention these kids and they multi MECpresentation but I'm going to talk alittle bit more about them now these twokits essentially provide everything youneed to to build a device driver exceptfor the unique pieces that would beapplicable to whatever device you'retrying to operate or whatever thefunction you're trying to accomplishso in these kits you get essentially askeleton of a complete working driverthat does nothing that will load and donothing then all that's required is toadd the unique pieces that you need todo whatever it is you need to do ifyou're trying to write a driver to Idon't know let's say talk to a piece ofhardware and you have a simple piece ofhardware like a serial port for exampleall you need to do is add the piecesthat talk to that piece of hardware tothe driver and everything else isprovided so a 16 bit driver I mentionedlast time there's really no limitationto 16 bit drivers because that's thedriver model that os/2 supports alreadyso anything that you can do in a 16 bitdriver any written anytheir way you can also do with the 16bit driver kit this the thing that hasbeen difficult all along with os/2 iswriting 32 bit drivers now this 32 bitdriver kit is significantly more complexthan the 16 bit driver kit because itprovides all of the funking modules allthe thunking functions it essentiallymakes all of the weird and crazy stuffthat's required to implement a 32 bitdriver completely transparent to thedeveloper you don't need to worry aboutanything other than writing your owncode in a 32 bit C module okay so itmakes it really easy the the differenceit provides a lot of things it providesa sealant all this all the C librarytype functions that you are normallyused to using and C applications itprovides like I said all the thunkingmodules it provides a heat manager allof this stuff in 32 bits so that thedeveloper really doesn't need to beconcerned about the peculiarities of a32 bit driver the only thing that is alittle bit different are the limitationsand the primary limitations come in inthe initialization of your driverIBM did a special thing for 16-bitdrivers that allow 16-bit drivers tocall a lot of the normal dose functionsat initialization time like DOS open dasclosed us read various other things sothat you can do file IO or whatever youneed to do to initialize your driver nowyou cannot do those things in a 32-bitdriver because those functions are notavailable and the main reason is becauseof a unique thing that IBM did when theywhen they implemented the driverinterface is that the initializationfunctions of a 16-bit driver run at ring3 not ring 0 my did I lose anybody thereok good now because of the way a 32-bitdriver has to run the initialanybody not know thunking okayessentially ring zero is the highestprivilege level thing there is a kernelruns at ring zero all drive devicedrivers run at rings Oh everything zeroyou can do anything you want there's norestrictions there's no privilegerestrictions ring three is the mostrestricted privilege level it's what allapplications run in applications run atring three and the reason there's thesedifferent privilege levels is becauseit's to prevent applications from doingkernel type things like you cannot youcould ring three you can only access thememory that's given to your applicationyou can't access memory outside of yourapplication that's just one exampleanother example is you typically cannottalk to the hardware at rating three anyi/o operations are blocked by the by theCPU because the CPU certain instructionshave different privilege levelsassociated with them and ring three cando anything but ring three like if youtry and do an i/o operation in mostcases you'll get a trap because the CPUsknows that ring three things can't doi/o operations they're not supposed tobe able to talk to the hardware now myoperations are kind of different becauseyou can assign iopa little to certainapplications and then they can butthat's a kind of a limited case soanyway that's the difference betweenthere were different rings ring zero wasthe kernel highest privilege leveldevice drivers typically operating zeroyou can do anything you want a trainedzero now ring three you can do almostnothing except talk to your own stone soanyway the reason that this becomes anissueis a being implemented device driver init time at ring 3 so specifically sothat it can access some of theapplication dos calls now when weimplemented ring I mean 32-bitapplication ice drivers we have to go toring 0 in order to convert to 32-bitmode which means that the initializationtime runs at ring zero which means youcannot access any of the ring 3 codethat was previously available to otherdrivers so you're very limited there andwhat you can do sometimes that's aproblem sometimes it's not so it alldepends what you need to do and that'sreally the the basis of the restrictionso let's move on a little bit Ohthunking thunking is the conversionbetween 32-bit and 16-bit or 16-bit to32-bit the kernel I mean the CPUactually operates in 16-bit mode or32-bit mode where the instructions areactually interpreted as 16-bitinstructions or 32 instructions and thedata pointers are actually interpretedas 16-bit pointers or 32-bit pointersand the stack can be a 16-bit stack or a32-bit stack so when you when yourdriver gets called by the kernel it'salways called at a 16-bit interface soit's called with a 16-bit code selectorand a 16-bit data selector so you needto thunk that to a 32-bit code selectorin a 32-bit data selectorand is gonna convert from the 16-bitstack to the 32-bit stack the driverkits do that before you and you don'teven have to think about that we'reordinarily you would have to think aboutthat and then when you return back tothe kernel it has to all be thumped backso that's what thunking issothere there is a ring too I am not awarethat there is a ring one it's not usedring 2 is used for some things like thevideo driver runs it ring 2yes yes that's different that'sdifferent the device driver does run itring to bring one is not used and theonly thing I'm aware of that runs itring to is the video stuff applicationsrun it ring three device driversrendering zero kernel runs it ring zerookayit is all do you seeI'm sorry what when you build it yeswhat's the difference the difference thedifference primarily is when they'reloaded base drivers are loaded very veryearly in the boot process and providebasic system functionality devicedrivers are loaded in a second waveafter all the base devs devoted that'sthe primary difference there are otherthere are other differences but that'sthe primary difference there is muchless system resources available to buyspace devs because they're loaded soearlythat's that's part of it yes that's partof it very little of the system isrunning when base that's load very verylittle there's no file system availableat when base that's load for example butthere is when drivers when devices areloadedthey do they provide very very basicthen across this one driver like hpfspajamas go soloand stuff like okay the main thing themain difference is when they're loadedbase devs are loaded very very early soif you need something done if you needto do something very very early in theboot process you would write a base stepor if you weren't just normal mostnormal I Oh devices are normal devicedrivers anywaythe driver kits make all of this stuffthey've been talking about very veryeasy and we haven't had this until veryrecently like I said it implements allthe memory layout stuff the systeminterface all the compiler setup stuffis in these kits so really you don'tneed to go looking and digging for a lotof information yesopen Wacomit also provides memory managementfunctions it provides all the thunkingfunctions in case you need to do somethunking on your own it provides a heatmanager memory allocation de-allocationmemory those type of things itessentially exactly provides everythingyou need except for this stuff that'sunique to your own application your owndevice whether it's a device if it's afilter driver not alder not all driverstalk to hardware some drivers just dosoftware things that things that need tobe done around zero that you can't do inan application like application helpersthis are very common so all you need todo is worry about the code for your ownhardware Hey any questionsOOP there's somebody here house c'monIRC can repeatoh yeah yes so what's actually in one ofthese kids I know it's kind of smallhopefully everybody can read thisthere's a kit directory whichessentially contains a library calledlike drive 16 live there's a header filewhich contains the headers for all thefunctions that are in the library andthere's a couple there's a few moreheader files one of the things that isimplemented in the driver kits is theend Asst and this modules because mainlyI wrote these to work on Ethernetdrivers network drivers so there's anIndus module and there's a PCI modulefor talking to the PCI bus for you soall of that is handled as well sometimesthat's a bit of work to dothen there's two other drivers to otherdirectories there's a required directorywhich essentially is the bare minimumrequired to build a driver and have itload it's got a driver dot C file and abase dev dot C file and a make file thatbuilds things so these are essentiallydrivers that will build and will loadand do nothing so if you wanted to startbuilding a driver you would start withone of those and just start adding inthe stuff you need in addition to thatthere's a sample directory whichcontains a real live working driver it'sa very simple driver that talks to ani/o card it's a plug-in card that hassome IO ports that you would use forsomething like home automation ortalking to whatever it's just it's justcentral aisle portsand it's a real live working driver italso contains test C which is anapplication that talks to the driverthrough the ioctl interface so you cansee a real working driver with realworking dos dev ioctlcalls and how those are implemented andyou could take that one and modify it towhatever your own needs are so I thoughtwhat I would do next is actually do thisI would take the the driver C file andmodify it to a to perform a very simplefunction compile it load it in rent inreal time so just to see how easy thatisI actually I already talked about thisthose are the two two examples of thetwo drivers that are provided in the kitand next comes a live demonstration sohere we go let's see if this actually Ican actually pull this offlet's see this willthere we go so I have a directory hereon my on my system that currently hasthe driver kit as you would download itfrom my website it's the zip file andeverybody see thatyeahthat's as big as it gets I could do afull screen session okay let's see if Ican do a full screen sessionyeahyeah let me see if I can get itwhere can I where do I find thesecommand I want a full screen promptsto directorno it doesn'toh yeah see your brain goes to mush whenyou're in front of peoplefull screen let's see now the otherprojector has to testI haveyeah there we gothat easier to seeso we have a 5/16 kit really once youafter you download it all you have to dois unzip it and it will create there'sthe directories that I just talked aboutit creates a kit directory with theheaders in it requites requireddirectory and it creates sampledirectory so let's move into therequired directory and there's the threefiles that we talked about now thisshould just build if I type make what Wmake okay except it's not going tobecausebecause I haven't defined I've been toldit where my kit is yet and what the wayyou do that there's help there's areadme that will describe all of thisbut what you all you really have to dobutis that an environment variableand then the driver builds so now I havea driver I have two drivers I have thebase dev driver that's built you can seebase dev that sis and I have driverthat's this now I could actually putthose into my config Isis and reboot andthey would load and do nothing soessentially just by downloading this kityou can build drivers anybody can okayit's true it doesn't do anything but youactually built the driver the whole loadyou do need the dvk yepyou do need the DDK and that's is onething that I already have installed andI have the ddk already installed and Ihave an environment variable pointing tomy D DK okayand you need open Wacom installsI also have Wacom installed Scott commonWacom and then all you need is theWhatcom equals wherever you're welcomeinstallation is and you can that'sfreely available you can go to the Wacomand download it and install ittemporarily I'm sureokay so let's do something let'slet's create our own driver let's startwiththere's a message open welcomethis is one reason I didn't want to goto fullscreen because okay this is thethis is the driver dot C file that isshipped with the kidit has lots of comments in it to tellyou how it works and what you need to dolike for example it says you must havethe strategy Handler and there is one inhere and it it does basically nothingthere's remember I told you that thefirst thing the kernel does when itcalls your driver it calls his strategyin it well here is your strategy in itand it says here it's called by thekernel immediately after loading yourdriver and the kit gives you thisstrategy in it call which is later on inthe file and what the strategy in itdoes is it sets the name of the driverhere I assume you can see this yep andit calls the kit in it which is thisfunction here is the drive 16 init whichinitializes the kit functions for youyou have to tell the colonel the size ofyour data segment and text segment codesegment and it output something to thescreen and it's doneso basically that's it so what we'regoing to do is we're going to add somecode to this which will respond to acopy command which a copy will open thefile read something from the driver andcopy it to the file it's really going tobe pretty easy so what we're gonna do iswe're gonna need to have an openfunction so let's add something calledstrategy open and we're gonna pass itthe request packet when the driver callsus when this kernel calls a driver itpasses a packet of information to thedriver which basically says what I wantwhat it wants to do and that's calledthe request packet and it pointed tothis request packet see when yourstrategy handler is called here it'spasses a pointer to the request packetso I'm going to I'm going to write astrategy open functionand I realize I might be losing somepeople butbut we're going to write a strategy openand a strategy close and we're alsogoing to need astrategy readso what I've done there is I've just puta call to strategy open in the strategyopen case of the case statement I put astrategy close in the strategy closedportion and I put a strategy readfunction in the strategy read okay soeverybody understands that okay so now Ihave to go write those functions solet's goand put those functions right before mystrategy hand alertyeah let's put it right yeahokay the first thing I need is somelet's definea buffer to stores the data in let'sjust make it like 1 K and we're going toneed a flag likesomething to tell me whether to fightwhether the driver has been opened ornot and some some sizes so that I cankeep track of how muchmy fingers on the right keys hereso we can keep track track of how manybytes of data the application has readand then let's startso I don't know if that was a very goodexplanation it's a pretty complexsubject and I tried to just do it in 30seconds but when the colonel calls astrategy read routine it's past thephysical memory address so you need toconvert that to something that that youcan actually write to and that would bea virtual address and a 16-bit driver soI'm going to do that so what I'm goingto do is first convert first calculatehow much memory how many bytes is leftto read which is how much memory howmany we've already read - how many weneed to still readget my fingers on the right keys hereoh I didthis should be read sizethis is the total size of the block ofmemory that can be read and the readcount is how much I've already readsothere we gowhat that statement does is I don't wantto ever return more bikes than was askedforif there's stillso far so goodhey you're catching all my compilererrors that would you manyeah that is exactly rightthat's itso all I did here is calculate how muchhow many bytes I'm going to return copyit from my message buffer to the virtualaddress I just got oh I did forgetsomething didn't I I keep talking aboutconverting this physical address to avirtual address but I didn't do itthose of you who have worked with theddk know what that isthat's the dev help of one of the helperfunctions that's implemented in thekernel to convert a physical address toa virtual address if that fails ofcourse I want to return an errortherenow we have a complete driver hopefullyit will compile and it should one anyquestions about what I've done so farone more thingeverybody understand what that what Ijust did thereI added my new driver to the list ofthings this make file will buildthe reason that happened is because Idid this in the fullscreen sessionbeforeall rightfixing my compilation errors whoopsthis is exactly exactlyI don't see what's wrong with that ohyes I dofor some reason my - keyit's really having trouble on thiscomputer since I used it lastnow what's wrong whatOh Ohthat's what you were trying to tell mebeforethere okay what I'm going to do is I'mgoing to copy itto the root of my boot diskjust because it's convenient place toput itI'm going to add a device statementas if I strike with more than 8yeswe're notI don't think so we'll find outone other thing that I want to show youin it before we is the name of thisdriveris right here this is the driver namethat's written into the header it'scalledmy DRV dollar you could make thatanything you wanted the you have eightcharacters maximum for the driver nameand it needs to be blank padded but thethe driver kit function handles all thatfor you so anyway it's there let'srebootno it's a regular driverthat might but this is not a base stepsee the line right there driver my driveloaded successfully that was the stringthat you saw in the init:functionstrategy in it when the driver is loadedso apparently it loaded it the colonelliked it it loaded itself successfullysolet's try copycan you see thatso I go go to a fullscreen sessiondoes that string look familiar that'sthe press printf that was in my driverso what I've done is this copy commandhas opened my driver did a read to readthe data from the driver and display iton the screenthat's something not too hard to donow if you need to talk to actualhardware your your code would lookdifferent than what I just wrotebut you know it's not not any morecomplicated you'd have to have knowledgeof the hardware that you're trying tooperate but anybody who can read adatasheet and write C code should beable to write device drivers and like Isaid at the beginning the purpose ofthis presentation was that maybe showyou that it's not all that daunting towrite that device driver anymore if youcan write C code and you can run acompiler and you have the DD K and youcan download this kit and you can get adatasheet for the hardware you want torun timethis time just maybe it'll inspire somepeople like if you have a an i/o card orsomething that you want to operatethere's no drivers for or somebody wantsto write a Bluetooth driver or somethinglike that you know give it a trywe also going to mention something aboutwow what a SAP issues welldevice driversas being issues thereyeah SMP issues exists for everythingnot just drivers SMP issues come up whenyou have more than one CPU trying to runyour code at the same time and you needto make sure that any resources that maybe shared that need to be protected fromaccess simultaneously by both processorslike if you have a chunk of memory thathas well like for example a good examplewould be if you do have a piece ofhardware and you have a hardwareregister that you need to write to - Idon't know operate your device if oneCPU is currently chunking out data tothis port and another CPU comes in andwants to do it and wants to talk to theport at the same time obviously you'regoing to have problems because what oneCPU is trying to write to it may not becompatible with the other CPU trying towrite to it so you use things like spinlocks or or mutexes or something to toblock access from one CPU so one CPUkiss complete access of this resourcefor the entire time it needs it so theother one will wait and won't try and doit this is this is normal things foranybody who's worked with multi CPUsystemsthe problem that we have with old stuffis smoke SMP systems didn't exist when alot of our code was written so nobodythought about it in some cases or didn'timplement it properly but now it now wehave lots of it's at these systemsthey're very common yeahyesyes yes because they're processed insequence they are processed in sequenceso yeah if you put it in in between onedriver and the other yeah it'll yourswill execute in sequence that they arein this in the config dices and howeverlong it takes it takesthere are there are drivers that alreadydo thatyeah there yeah I have a driver thatdoes that the thing that you need to tobe aware of is like I was talking aboutearlier bass deaths operate very veryearly in the boot sequence so there'snot very many resources available to youso any delay that you do you can't likemake system calls to do it you have todo right there in your own code yeahsomething like that yes there's aquestionnaire on the IRC channel andsomebody asked to looked everywhere mr.ed mr. edand any witness is asking why should Iuse the 32-bit driver instead of the 3216-bit bloody bondages and deviate thattheir officers that 14 32-bit driverseasier yeah typically if you're gonnastart writing an original driver thenit's a fairly simple thing to do the16-bit kit is the is the easier one touse if you're gonna port a driver likefrom Linux or from somewhere else that'swritten written as a 32-bit driver soyour C module that you're gonna pour itand try and recompile is is already a32-bit source code then you're betteroff using the writing a 32-bit driverbecause you'll have less problems inyour C file your variable sizes in a16-bit driver at 16 bits the variablesizes in 32-bit driver 32 bits and thatcan be an issue sometimes unless thecoder has thought about that soyeah for porting stuff the 32-bit isprobably a better choiceany other questions I have no moralhigherthat's why when I in the multi Mac Iwent to the 32-bit stuff for the for allthe stuff that I'm currently porting itjust makes the porting job easier plusyou have unlimited code size in 32-bitdriversyou don't have the unlimited data sizeyou cannot you can always allocate asmuch data as you want by allocating itfrom the kernel but your data segmentsize is fixed at 64 Kokayanything else well hopefully this wassomewhat informative I kind of it wasvery simple and meant to be introductoryand meant to not take very much time soI kind of skipped over a lot of detailbut hopefully you see that how to usethe kit and how easy it is to actuallyget drivers built these dayswell yeah that would have been nice andI don't know why it wasn't done alreadyand there are tools like that like theDDK has has a lot of things that arecommon but it wasn't organized as nicelyas thisand one of the things that the kit doesfor you is it gives you that thefamiliar C environment with your normalseat calls like mem copy string length sprintf printf those sorts of things thatyou're used to using all the time thatare sorely lacking in the normal whatpast driver environmentsyeahI know there there were changes to the DD K so I honestly I can't answer thatquestion to what you're gonna findit's probably gonna be fine I knowthere's a couple files that got updatedto be compatible with the open watt commstuff send me an email if you havetrouble with thatokaythere's another question here aboutthat's I think that's beyond the scopeof your presentation being that thishouse key here what about the PSDa PSD is a very very special devicedriver it's well it's it's not really adriver in this in the sense of thesedrivers it's it gets loaded via adifferent kernel interface it's atotally different animal totallydifferent and it's not within the scopeof this presentationwe didn't say that PSD villainsvery extensional it is I was just gonnasay that a PSD is a kernel extensionit's a kernel plug-in it's it's not it'syes you could think of device drivers askernel plugins too but it's a it's adifferent interface it's it's a thingthat the kernel nose has intimateknowledge about the interface of the PSDthat PSD is a PSD stands for platformspecific driveranyway if you do decide to try and writea driver there are other examplesbesides these in the kit the multi mapdrivers use the drive 16 and the drive30 to kiss you and those are open sourceyou can go look at those and see howthey were done as like I said yesterdayenvy ETF and II 1000e used drive 1681 69and e 1000 be used drive 32 so there arereal life examples of real life workingdrivers that are in use and inproduction that use these kits and youcan always take one of those as astarting point and and modify them tocreate whatever you want a Bluetoothdriver for exampleyou know or whateveryou know whatever yeah so that's theconclusionyou're very welcomeno other questions