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‫Hello and welcome in in this lecture, we are going to prepare our bootloader for being booted on a

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‫real machine.

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‫Now, in most cases, this current bootloader will run just fine.

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‫However, some biosphere's, including my boss, will tamper with your data if you put your bootloader

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‫from a USB stick.

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‫Now, the reason this happens is because of the bio's parameter block.

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‫Some bosses expect this while most Bias's will not corrupt your data and will work just fine with the

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‫code that we have here, some will actually stop filling in information and it's important this doesn't

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‫happen.

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‫So here you can see things like number of sectors per cluster, number of reserve sectors and so on.

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‫My bias actually replaces these numbers in memory with numbers of its own, because when we boot from

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‫a USB stick, we're actually doing something known as USB emulation.

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‫The bias is treating our USB stick as a hard drive or hard disk and allowing us to talk to it as such.

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‫So you don't really need to know too much about the bias parameter block right now.

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‫You just need to know that some biases assume it's there and we'll start writing data overwriting your

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‫code, which can lead to problems.

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‫For example, our little program here will boop for me.

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‫However, this jump instruction here is corrupted, so it causes my system to just keep running code

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‫and ram.

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‫It never stops.

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‫So we get around this problem by implementing the bias parameter block, we don't we don't have to have

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‫real values.

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‫It can just be all zeros and we can just have a fake one just to get around this problem.

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‫So the first thing we do is, is we add up the size of the bias parameter block, except these three

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‫bytes because these three bytes are short jump and no operation and some biases will look for this as

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‫well.

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‫So we're actually going to write that in, but the rest will be all fake.

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‫So I've added those up and I've come up with the value of 33.

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‫So that's the size of it, apart from our shot.

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‫Also note, this is Osterberg.

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‫It's a fantastic resource for people wanting to develop Col's and operating systems is very detailed.

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‫Some stuff's out of date, so make sure you check.

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‫So if you ever decide to use this website, make sure you check multiple sources if you run into problems.

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‫Right.

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‫So we need to actually basically just make 33 bytes.

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‫Now, bootloader so that if your bias is like mine when it comes in overwrite stuff, it isn't actually

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‫damaging your code.

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‫It's just writing into your fake BIOS parameter block.

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‫So we go back to Visual Studio Code.

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‫What we're going to start by making our.

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‫Short jump here that expects this three bites in size, right?

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‫So it's a short jump in and no operation.

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‫So we're going to start by doing that and we do that by creating another label.

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‫We'll just go under scroll start and then we're just going to go jump shot start, OK?

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‫And then we're just going to go up by here and this this line of code that we have here.

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‫We'll need to be copied.

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‫And we'll need to place that here.

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‫OK, and we're just going to replace the star with step two, something like that, and then we're just

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‫going to put step two by there.

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‫So I know that's a mouthful, but then our bias parameter block will go in the middle by here.

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‫Right.

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‫So just to clarify what we've done here, we've created a new label, Underscore Start, that just jumps

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‫to our star label here.

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‫And this is also a short term project.

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‫And we have a new operation here as required for our bias crime to block as well.

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‫So then what happens is the problem comes in here, jumps to our star label here, OK?

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‫And then we jump to step two.

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‫But we we specify the segment zero seven zero.

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‫So the code segment register gets replaced with zero seven zero.

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‫Right.

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‫And then it'll start executing step two, which will print our message.

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‫So in here, then we need to go time's.

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‫And the value was, I think it was 33 times 33.

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‫DB zero.

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‫So all this will do then is it will create 33 bytes just after our short jump here and that is our bias

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‫parameter block.

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‫So if your bias does stop filling in these values, it doesn't corrupt your code.

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‫It just fills in these no bytes.

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‫So it's perfectly safe.

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‫OK, let's just assemble that and see if that works as expected.

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‫So we just go, Nazeem Dasch have been booted, Assem, Das Show, Boot Dobbyn, and then we're going

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‫to run Kumu.

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‫And we see how global, so that works fine on the emulator.

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‫And I think now we're ready to test it on your real machine.