[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[Bug 1608802] Re: READ_DMA (0xC8) command does not work correctly

From: Launchpad Bug Tracker
Subject: [Bug 1608802] Re: READ_DMA (0xC8) command does not work correctly
Date: Mon, 18 Jan 2021 04:17:17 -0000

[Expired for QEMU because there has been no activity for 60 days.]

** Changed in: qemu
       Status: Incomplete => Expired

You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.

  READ_DMA (0xC8) command does not work correctly

Status in QEMU:

Bug description:
  The QEMU PC emulation of DMA does not behave like real hardware or
  other virtualization software.

  From the original bug report (Benjamin David Lunt):

      Back to the READ_DMA command, it is my conclusion that the
      READ_DMA command, more precisely, the BUS Master part of QEMU is
      in error.  The tests that people have done to see if it works, is
      probably the guest finding out that DMA doesn't work and defaulting
      to PIO, but since the read was successful visually to the user, the
      user assumed the READ_DMA command works, where the guest actually
      defaulted back to PIO transfers without notice.

      My code works on real hardware (numerous machines), Bochs, and Oracle's
      Virtual Box.


      I have a small test suite, zipped and included at:

      Within this zip file is a.img. This is a freeDOS bootable
      floppy.  Emulate it with QEMU and then at the DOS prompt, run

      It will say that the drive is not ready.
       "Drive never became ready"
      (along with a few other lines of text)

      The source for this test suite is also included.
       c8bug.c is the c source code
       c8bug.h is the header file
       ctype.h is a quick way to get 'bit8u' type defines
       timer.h is a delay routine from another project I have
      (The base IO addresses are assumed and set at the top of c8bug.c)
      (compiled with DJGPP for DPMI)

      q.bat is my command line for QEMU

      On all other machines and VirtualBox, the controller is ready
      for me to receive the sector data.
       "Drive is ready to transmit data..."

      However, in QEMU, the controller never becomes ready.
       "Drive never became ready"

  The bug was reported for QEMU for Windows, but I can confirm that QEMU
  for Linux also shows that behaviour, while VirtualBox works.

To manage notifications about this bug go to:

reply via email to

[Prev in Thread] Current Thread [Next in Thread]