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Hello.

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So in this next lesson we quaint.

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Take a look.

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How to declare variables in assembly.

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Show us.

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We always do.

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I create a new photo on my end and call this one variable

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in sin and then I'll just name the project variable and then open and select our board t up for C 1

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2 3 0 h 6 p.m.

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okay and then under CMC is to call on a device to startup and then we come here.

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Targets options were set to the 16 mega heads and then debugger distilleries I C D I OK we're all set.

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So like our previous program we're going to have to follow us here.

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One assembly and then one C we do some of the work in assembly and cool it in C so I'll create a first

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for here and then I'll press control X to save this empty file and what's the name of the group on this

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one and I'll call it function Dot.

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S just like the first program we created and I would say this one too and pull this one main let's see

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after the double click here and then both files.

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Then we could and then we start by right now the content of our function not C.

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And over here we're going to introduce something new so far in our assembly code we've declared the

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directive area and we've specified that the area is the code area.

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And this lesson we're going to specify another area known as the data area.

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That is where we would store our data.

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So let's take a look at how this would go.

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This is going to have two areas.

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So there's the clear area.

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What area is it.

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It's the data area.

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And then there's a line and a line 2 and then to create a variable you give the name of the variable

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US label.

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Let's call this scramble amount.

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That's the name of our variable and we use the directive space and then we indicate the amount of space

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we require this number for each space as abides.

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So if we won here this would be one byte space which is equal to AIDS bits but we want 32 bit.

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We want our variable amount to be a new 32.

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So for here given this 32 bit.

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That being said.

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So what we have to do to make this variable callable outside this file.

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We have to export it.

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So we'll use the export keyword export amount.

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So we've declared the we've declared a data area in order to make this visually appealing.

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I usually do this for beginners.

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I declare one area and put a line and then declared a second area.

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So you can do this.

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This not necessary but I think this would help you understand it entirely a little way to the next area.

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Just normal area code area where we put a program code.

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So we start with the area directive and then we start with the text to make it callable in C.

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Then we make sure we tell them what area code and it's really only a line

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a line 2 and it's thumb.

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We write and inform instructions and we're going to create a function that function to contain our variable.

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So we might as well export the function.

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Otherwise we wouldn't be able to find it.

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Let's call this function and march function for that amount.

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Func OK let's just call it this.

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So you can see the difference.

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These two things these two items we export to this first one is variable code amount and this is a function.

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So we want to use them outside this file hence export.

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So we come here to write the contents of the function start with the function name and label to amount

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on the school C

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and we come here and basically what we're going to do here is load the variable here and put a value

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in the variable so we're going to do by do that by pointing to the variable and then swap in swap into

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value from one register to the variable you can think of this as how we manipulate the bids in our GC

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GPI registers yeah our RC GC GPI and then a standard GPA it will registers registers festive for we

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used to use the Delta are two point to point to these registers and remember the registers where the

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registers with names like GPI both data underscore ah they were just place holders there were names

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with give into the address to the address of that particular registers.

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So you can think of the word amount as such a name such a name would place and a location in memory

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which would be served here a space for two just like we did just like we did before by writing system

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c c l I received GC keeping on a score Ah it's just an example of this what we did before yeah we pointed

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first and then we toward add value later by using L2 R and then by doing this as you are one to get

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the funding into our one two.

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So after these two lines we end up with whatever value comes here in this register.

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So this time we point to our variable amount.

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And then let's move the value to another register let's say we want to store the number 89 in our variable.

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So we have 89 nine here.

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So to store we just SDR is a shorthand 0 0 and then I 1 remember as the r source the source is the number

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eighty nine.

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And then we store in what are is pointing to which is the memory location of all of our variable to

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at this point we've stored 89 in the variable amount and then we returned from the function x r and

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then we line and we.

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And so we've created a variable here and you can create as many variables as you want.

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Yeah.

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So this what it looks like a new addition to this side would be declaring the data area and declaring

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this you've not seen this before.

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So pay closer attention to it.

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So now that we've finished with this and we've exported this and this we can go to the seaside to to

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right out the C code and let's let's conclude it as to the end so that we can be able to use you into

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theta to include best and that's h.

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Sorry we have to use the keyword external to call our variable cos it's external.

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Yeah it's literally external

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and the name of the variable is amount plus we gave it and we have our function which is a int to return

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a good amount on this call in C and tennis and forward

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shall we have this in this too.

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That's great on Main function in Spain.

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And we have me here.

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So let's call our function our function from the assembly scored amount amounts func.

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Yeah okay.

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So let's go back and take a look at the function again of our voice here it's empty.

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It is through this function that we add something to the variable.

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That is why we have to call this function here.

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This just for this experiment to see that actually we've stored something in the variable.

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So in order to do that remember this is the global variable here.

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There's this fair amount.

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We have it in C here.

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So we can just read this and see whether indeed its value is eighty nine after the function has finished

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running.

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So all we have to do is call the amount here.

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You can just call amount we assign it to another variable.

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So let's create a global variable here call you in 32 weeks to end and let's call it C amount we just

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create this global variable and then we assign C amount

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to the the amount value.

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So remember this amount is this amount is the same thing if we are to change to name to something else

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the code wouldn't work.

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So we just want to read the value of this file variable in assembly and displayed in this new variable.

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This is just for display sake.

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If we wanted to do a computation we wouldn't need this redundancy of writing one other global variable

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to display this in a way I wouldn't confuse you.

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Let's check.

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And please remember to put what I do not understand in the comments line you would receive a prompt

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reply.

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So what we have to do now is to compile and we have zero errors with download onto our board

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and we reset our board when we are done with that.

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We just opened the door for you

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and this time what we interested in is this is this global variable here amount we can just add it to

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the watch window to see what happens in it.

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Come on do this highlight right click and then up to 21

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and once that is done we can just step through the code you can check this to display in decimal form

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so once we done we can just pick over and see the changes that occur in the code so we can see we have

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the value 89 89 is stored in our variable here.

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This extend or variable and we've read in it from our new global variable.

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So indeed our variable is working from assembly to see.

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So show you more.

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Let's say we were just closed as we cleaned this.

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We don't run this C function or the code runs all right.

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A variable wouldn't work cause it was the function that was doing the assignment for us so yeah

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let's see

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if she can see nothing happened.

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Yes.

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So yeah this is how to write a variable in assembly.

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I hope you get to so in the next lesson it would take a look at how to import functions from C and use

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them in assembly.

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C You.