Chapter 21 Demo Released

[Mike]

Hello everyone,

The VPC compatibility bug has been fixed in this new demo, and the demo builds off of the code in the chapter and last demo to read sectors from disk using our new DMAC interface. Everything is set up for us now to read and execute a program - coming up in chapter 22. The chapter has also been officially released with some new content.

[djsilence]

1. You wrote in help cmd about reset but forgot to implement case of that
2. Like prevoius chapter, demo of this one doesn't work in VMWare (very seldom it works).

Daniel.

[Mike]

Hello,

I must have messed the reset command - I will be sure to fix that. I have not tested in VMWare. If it is possible to explain the exact issue and what happens I will be sure to look into resolving them.

[djsilence]

See, while trying to read some sector you can get to results:

1. You get right values of sector, but after it if you try to read one more you get infinity loop (I guess, because nothing is displayed).

2. You get wrong values of sector (some strange values like a 0x00, 0x01, etc.) but then you can read it more and more.

Conclusion: if reading is right - you can read just one sector, if reading is wrong - you can read any number of sectors.

Daniel.

[ehenkes]

The VPC compatibility bug

Could you please comment about this bug? (before/after)

[Mike]

The VPC compatibility bug

Could you please comment about this bug? (before/after)

Hello,

Basically VPC does not seem to like setting the DMAC to auto-reinitialize. It is fixed after clearing that bit and re-initializing the DMAC before every read or write. This was verified to be the case when we tested both demos.

[Tubash88]

Hey Great series, Love it. I have read each chapter 2 times. and am planning on Reading them all for a 3rd time. Everytime I read it I learn something new and I also get something better.

Just a question. When will chapter 22 be released? No pressure, Just wondering. Do you have an Estimated Time/Date?

Keep up the great work. I am learning a lot from these tutorials, and I am also reading the Documents from OSDEV.com. =]

Well, I am eagerly awaiting the release of the next chapter.

Keep up the great work Mike.

[Mike]

Hello,

I apologize for the late response. I am planning some updates in earlier chapters (more specifically, the virtual memory management chapter) before continuing. I plan to add a stronger emphases on virtual address spaces and their use in multitasking to the chapter and managing and working with virtual address spaces. Possibly an update to the demo as well to make it easier to work with.

[djsilence]

Hi, Mike!

I had a real problem with demo 21 in vmware - because of strange things happened. now i installed vmware 7 and got more "excatly" problem: I just get Error reading from disk at any time with any sector I'd like to read.

Daniel.

[Mike]

Hello,

Do you only get the problem with VMWare? ie; does it work in Bochs and Virtual PC?

[djsilence]

yeah, just in vmware)) i don't know what can it be because even different versions of vmware gives that problem))

[Mike]

Hello,

I am going to have to mark it as a compatibility bug with the series. The demos are only tested in 2 versions of Bochs and Virtual PC before releasing. The issue will be looked into.

[chibicitiberiu]

While going through the code, I noticed this:

Code: Select all

//! resets flipflop
void dma_reset_flipflop(int dma){

   if (dma < 2)  // <- ERROR! Correct would be: if (dma >=2 ) return;
      return;

   //! it doesnt matter what is written to this register
   outportb( (dma==0) ? DMA0_CLEARBYTE_FLIPFLOP_REG : DMA1_CLEARBYTE_FLIPFLOP_REG, 0xff);
}

I found it in demo22, but since it is built based on this one, it probably has the same error.