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diff --git a/nx-X11/programs/Xserver/hw/xfree86/os-support/os2/README b/nx-X11/programs/Xserver/hw/xfree86/os-support/os2/README deleted file mode 100644 index d07059eed..000000000 --- a/nx-X11/programs/Xserver/hw/xfree86/os-support/os2/README +++ /dev/null @@ -1,78 +0,0 @@ -Information on files in this directory --------------------------------------- -\xc\programs\xserver\hw\xfree86\os-support\os2 - -The files in this directory form the OS-dependent porting layer of -XFree86 for OS/2. They are the work of: - - Holger Veit <Holger.Veit@gmd.de> - Sebastien Marineau <marineau@genie.uottawa.ca> - -Some functions which were absent from OS/2, -such as direct access to IO ports and the mapping of physical memory, -are implemented in a device-driver written for this purpose by Holger Veit -<Holger.Veit@gmd.de>. The driver also implements several functions -necessary for xterm. -The driver should be installed in the config.sys with a line: - -DEVICE=path\XF86SUP.SYS - -The following gives a brief overview of the implementation of the -porting layer, and lists some of the "gotchas" when modifying the source. - -BIOS and physical memory mapping: This is handled by the functions in XF86SUP.SYS driver. - -IO permission: Handled by a function in the XF86SUP.SYS driver. Essentially, IO permissions -are granted for the whole Xserver at server initialisation. The device-driver sets the IOPL -level to ring 3 for the Xserver, which in essence gives it the same IO privileges that a -device-driver has. Note the danger here: the Xserver can write to any IO port it wishes, -and can disable interrupts (something which it does), thus can potentially hang the system. - -VT switching (switching back and forth to the WPS): This is handled by the keyboard driver, -i.e. the stardard keyboard sequences (CTRL-ESC etc.) trigger the switch back to PM. The -Xserver is notified of switches by the VIO function VIOSavRedrawWait(), which is run in -a separate thread. When a switch to/from PM is requested, this function call unblocks, and -the Xserver either saves or restores the video buffer and video mode. Note that semaphores -are used to communicate with the main Xserver thread, and handle cases such as server -reset while the server has lost focus etc. -A similar mechanism is used to handle hard-error popups. A thread is run which blocks -on the VIOModeWait() function. When a hard-error notification occurs, the Xserver attempts -to recover by resetting the screen. Note that, due to some (probable) bugs in the OS/2 -video drivers, this does not always work as expected. According to the specs, the OS/2 -video drivers are supposed to restore the palette when returning from a hard-error. This -does not seem to be always the case..... so the palette in X may be screwed up after the -hard-error. - -Keyboard input: because X needs all keyboard event to function (both keypresses, key -releases, for all keys), the keyboard input was implemented by registering a keyboard -monitor for the Xserver. The keyboard monitor is run in a separate thread, and sends -the keystrokes back to the Xserver main thread through a queue. Another thread is -also started, whose purpose is to "eat" the keystrokes returned by KbdCharIn(). Note that -the monitor was necessary because the OS/2 keyboard driver does not pass all keystrokes -to the application calling KbdCharIn(). - -Mouse input: This was implemented similarly to the keyboard input: mouse events are -read in a thread, which then passes them to the main Xserver thread through a queue. - -Select: this unix and emx function has been reimplemented and optimized for the xserver. -Because of the need to handle input from pipes, sockets, the mouse and keyboard (which -select() in unix does but the EMX select does not), it was decided to rewrite it in -order to minimize CPU usage and maximize responsiveness. Essentially, select() blocks on -a MuxWait semaphore, and unblocks when input is available from pipes, the mouse and the -keyboard. The MuxWait semaphore times out every timeslice, so that sockets can be checked -for activity (unfortunately, sockets are not well-handled in the OS/2 TCPIP and one cannot -attach a semaphore to a socket). There is also the possibility of using the high-resolution -timer (found in Merlin) to check sockets more often than every timeslice. -*** Important: in order to maximize speed, certain shortcuts are utilized in this -implementation of select(), which makes it unsuitable as a general-purpose function. Also, -it is imperative that the EMX select() never be called from the Xserver! *** - - -If you wish to modify the source, be aware that there may be very good reasons as -to why certain things were done this way. Usually, if certain function implementations -appear unnecessarily complicated, it is probably because there were subtle problems -with the simpler solutions. Due to the complexity of the Xserver code, and the -differences between OS/2 and unix, there are many potential pitfalls. - -$XFree86: xc/programs/Xserver/hw/xfree86/os-support/os2/README,v 3.1 1996/01/30 15:26:27 dawes Exp $ - |