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Hello.

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Welcome back.

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In this lesson we are going to see how to write a drive for a while.

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Cystic time.

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And then we going to use the cystic to create a delay function to create precise delays in this experiment.

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I'm gonna create a new project by coming over here.

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New York Vision Project I store it in this forward I've created a name called the cystic

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and my port is Tim for C 1 2 3 0 8 6 p.m.

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and then under this UMC is select to call on a device Austerlitz startup.

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Okay

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I'm gonna come over here.

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My target is the team full support team for C 1 2 3 Use you each.

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I'll just make it to 4 see 1 2 3.

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And um she was group here.

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This is up and then create a new fault here.

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This is a mate.

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Oh.

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Make it s mean that s cool it made notice like this.

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Okay so um we're gonna write a driver for the cystic timer so the cystic timer is a cool pair for all

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of um cortex M and what I mean by copay for is that this this is included this is included in the architecture.

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So this is not ordered by the silicon manufacturer.

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And what I mean is this.

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Okay.

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Before I continue.

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For those of you who don't know the UM WE SAY UM cortex M for cortex M 3 etc..

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Um is a company based in Cambridge UK.

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And this company does not manufacture any hardware.

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They don't produce hardware.

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If Tesco excellent engineers who come up with designs and then they sell the license of their designs

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to people to companies I should say so.

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S t microelectronics has it license from um Texas Instruments has a license from um.

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Apple has a license from some source a license from um while we has a license from up I could go on

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and on.

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In fact it was estimated that over 90 percent of mobile phones out there use um architecture.

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But the one used in mobile phones is the cool text a architecture not a cortex m a stance for application

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M stands for microcontroller.

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So we are dealing with the cortex microcontroller right.

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So when I say since this is part of the core architecture I mean when you buy the license or when you

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sign up for a license from um the car designed to give you a full context M cystic is part of it.

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So it is up to me with a silicon manufacturer to add at a peripheral such as the ADC that you are to

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the US be the SBI ITC etc. those at a per force are included by this uh by the by the silicon manufacturer

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but by the cystic timer is part of the call peripheral.

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So mean in the court we write over here for cystic should work on an equal text M for board the same

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way because the address is the same.

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This is not decided by the silicon manufacturer right.

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So because of this to get the M to get the address of the cystic registers we are going to go to the

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cortex M We're going to go to the cortex and generic use a guide rather than go to a what team for C

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datasheet.

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We're going to go to the generic you said guide provided by arm with regards to quote text M for so

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you can just come to books over here and select cool text M for generic use a guide.

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Right.

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This is it.

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This document is provided by arm.

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Right.

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So what we want to do is find the um find the cystic register this um in the generic use guide.

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Let's see.

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This should be a page that tells us the Memory map of the copay froze.

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Okay so over here we we have context M for poor folks.

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So all of this is included in cortex M for us the call when you buy devices.

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So I'm gonna click on the cystic timer over here.

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Let's see what we have.

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Okay yeah.

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This the cystic time.

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So these are the cystic Regis this and over here.

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It gives a short um short so explanation for cystic.

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It says the process has a 24 but 24 it s type system timer narcissistic sort of what cystic is an abbreviation

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of assistant timer.

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This time a count down from a reload value to zero re lowest.

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Then it reps to the value in the cystic reload uh fully register.

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I think that is a R V R is reload value register.

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Right.

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So each item registers machine will need for our cystic timer so we have to create symbolic names for

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these registers.

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Right.

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So let's start of uh let's start with the cystic control register.

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This one here since they control and that is register we're going to call this we're going to give this

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registered in name and Vic system control register because when you take a look at the um the driver's

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provided by the silicon manufacturer we can take a look at your Texas Instruments your team 4C 1 2 3

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0 8 6 p.m. dot age 5 that is often provided by Texas Instruments for people who do want to write the

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bare metal code.

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We take a look at this head of the name.

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They've given this registers we're going to use the same naming convention.

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So it's often called n Vic and Vic um it s written like this and Vic and n VIX times for ness uh ness

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that effect or interrupt controller and then SD for cystic and then we say C T C T R O for control and

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then R for register and this the address here we just get it.

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This is the address for this is the control register.

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So it does the naming convention which we use for this right after the.

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Let's see.

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We also need the um the cystic reload value register.

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We're going to call this one and Vic and I echo SD and this called reload on let's school R and then

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we give a symbolic name.

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Uh this the symbolic name will bring the actual register.

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The actual code.

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There we go.

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So after this let's take a look at the next register.

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This is the current value register.

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Copy it.

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We simply are going to call this cystic current to register.

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I'll say and Vic SD current on the score.

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Are you.

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Q You and this.

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Right.

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So these are the three important registers we need for this experiment.

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We don't need this last one the collaboration register we don't need it so we can read up a bit uh about

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this.

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So this is the control register the control register as you can see we have better numbers you were

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1 2 to 3 to 15 our reserved but 16 is used for the count flag bit 17 to 31 are reserved.

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Let's see the meaning.

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Okay.

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It's 16 counts luck This returns one.

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If the time I counted to zero since the last time this was read.

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So this is where we use this flag to check what out a what time out hustle kit which is located at bits

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number 16 of the offices the control register and button number two indicates the clock source.

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What are we using an external clock or an internal clock which is a process a clock.

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This is between number two if we are using our internal process a clock we have to parse one two bits

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number 2 over here.

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Code clock source it's number 1 is known as the tick interrupt.

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This enables systemic exception request and it s s 0 counting down to zero does no I said just take

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exception requests weren't counted down to zero except to basically use this to enable the system interrupt

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or exception and then bits number zeros to enable the counter.

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In other words to a neighborhood assisted time timeout so we use pit number zero to do that when we

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pass one we've enabled it to one policy we've disabled it so that is the system control register right

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and the rule load register specifies this that the value to load into the cystic um current value register.

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Right.

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And over here it s it s twenty four bit the maximum value we can load into the reload registers 24 bit

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from zero to twenty three over here and over here it's reserved.

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So we load our value here to reload value can be any value in the range of your x years or 1 2 0 x and

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this is the maximum 24 bit value.

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Okay.

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So okay so you can come back it can come back and read more about the Sestak if you want to learn more

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for that but we're going to create symbolic names to represent these other things such as things like

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the clock so screws in the clocks also enable disable the tick interrupt and enable disable the timer

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will create symbolic names to use for those um I'm gonna come down here and I'm going to say and Vic

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gets the control count this would represent the count of luck we'll see it can you and I'm simply going

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to pass this

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this pits number sixteen This sets bits number sixteen to one in the control register and then I'll

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say and fake

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s t control clock SOS.

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This will allow us to select into our process a clock source or an external clock source.

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Q You

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I'm going to pass one to that particular bit and if you explain this for you would realize that one

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enables the bits that select the process a clock source for us and then next interrupt enable when I

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use an interrupt in this example.

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But when we start dealing with interrupt you need this as the control and then into enable a queue you

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I'm gonna pass this here

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next is to enable

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and we enable through the control register and Vic as the control register enable

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c e q you over here and then we know pit 0 is for enabling.

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And then next a reload value you gonna say n fake SD.

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Um s t reload would put us in the reload register.

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M P to you and then we're going to use the maximum 24 bit value Okay so I just put a comment to this

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what it can't flag.

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This over here is for cluck sauce.

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This is for interrupt enable or interrupt

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and enable counter mode.

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And then there's the current load value

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right.

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So the next thing we have to do is bring in the um the registers for a while the registers for our LCD

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because we want to make an LCD blink.

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So because we've already learned how to create symbolic names for our registers which in regards to

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GPL your output would need not do that from scratch.

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I'm just going to copy it from the previous project and bring it over here.

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Copy this pasted over here like this.

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So we've got we've got a direction to teach to enable the data register.

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Yeah.

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And then um symbolic names for enabling GPL u f as well as our LCD and then not a symbolic name to turn

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off the red LCD.

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We're gonna be using the red LCD here right.

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Right.

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So we are done assigning symbolic names to our relevant registers.

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Let's continue into next lesson.

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Let's implement to what driver.

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I'll see you later.