Overall, PIO mode is a slow transfer method. The palette is set up as a byte array. That works fine However, I want to make it interactive, i. Drives only respond to newly written values of nIEN when they are the selected drive on the bus. I won’t explain much of this, because I think that’s another tutorial. Let’s take advantage of this in the next Source.

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Cylinder, Head, Sector mode is completely obsolete, but there are a few things to know about it, for legacy reasons.

Sign up or log in Sign up using Google. See the “33 bit LBA” driver code below. There is a special IO port bit that allows a driver to select either drive as the target drive for each command byte.

VMXh-Magic-Value – aldeid

Or, a driver can poll one of the Status ports either the Regular or Alternate Status. This way we get into and out of mode 13h: It also opens up the field of power-efficient computing to a wider range of researchers by providing a power evaluation methodology within the portable and familiar SimpleScalar framework. The reason loport read the port before writing anything is that the act of writing can easily cause the voltages of the wires to go screwy for a millisecond since there may be nothing attached to the wires to control the voltages!


After a CMP conditional instructions can be used to act on the result of the compare. Alternately, you never want to send new commands to a drive that is already servicing a previous command, dmp. MUL – Unsigned Multiply. We need to keep a counter of the pushed values, because if we pop or push to much, the RET instruction will go wrong.

CMP IOPort Driver Drivers

Okay, how do we get into a different video mode? Okay, what is Chapter 4 about? If the number is negative highest bit is set it will fill it with 1 bits. This code might look like you’ll never use cm, but in some programs it can be very useful.


You can set them if it will make your code cleaner to use the same magic bits as LBA Doing so is much slower than doing two outb commands to different IO ports. The least significant bit if “pushed” out of SI into the carry. This will reset both ATA devices on the bus. Then we make AX 0 because we want to start at the first colour in the palette, we output this to the port. With the knowledge of ASM you now have, you should be able to make a program already.

Before sending any data to the IO ports, read the Regular Status byte. And as always you guessed it I hope you learned something.


So you only need to do half as many tests. W e’ve already seen the DIV instruction, but there are much more mathematical instructions.

ATA PIO Mode – OSDev Wiki

So this is what we get: Their functionality is almost completely identical. CHS mode is obsolete, but is discussed quickly below. So maybe something like: Kris Kamweru 6 4. If the value read is 0, the drive does not exist.

So if we would SHR an 8-bit number, -5, 2 bits, the result is b.

By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies. However, when a computer is just beginning to boot there are no other processes. All conditionals jumps can be used to test the flags, so if an Overflow occurs a JO can be used.

Then read the Status port 0x1F7 again.