xref: /xsrc/external/mit/xorg-server/dist/hw/xfree86/int10/INT10.HOWTO

                 INT10  X86 Real Mode executor
                 =============================

		         PRELIMINARY

INT10 is  a XFree86  module for soft-booting  and executing  real mode
int10 BIOS calls. The BIOS call code is largely untested, yet.

1. Usage
========

To   use   the   int10   module   in  a   driver   the   header   file
xfree86/os-support/int10/xf86int10.h must be included.

 a. Initialization
 -----------------

The int10-executer gets initialized by calling:

   xf86Int10InfoPtr xf86InitInt10(int entityIndex);

The  function  will soft-boot  any  non-primary  device  and return  a
pointer  to a  xf86Int10InfoRec on  success. If  anything fails  or if
int10 execution  is disabled by an  option in the  device section NULL
will  be returned.   The driver  should store  this pointer  for later
calls to other int10 module functions.

 b. Memory allocation
 --------------------

To allocate memory in the real mode execution environment
    
   void * xf86Int10AllocPages(xf86Int10InfoPtr pInt,int num, int *off);

can  be called.  It  allocates num  consecutive  pagesize chunks.   It
returns the address of the allocated area. off is set to its offset in
the real mode memory space.

  void xf86Int10FreePages(xf86Int10InfoPtr pInt, void *pbase, int num);

Is used to free num pages beginning at pbase.

 c. Doing int10 BIOS calls
 -------------------------

The BIOS call is executed by calling:
   
   void xf86ExecX86int10(xf86Int10InfoPtr pInt);

The number  of the interrupt (normally  10) and the  initial values of
the ax, bx, cx, dx, si, di  and es x86-CPU registers can be set in the
xf86Int10InfoRec  passed to  the function.   On return  this structure
contains the  exit values  of the registers  listed above and  the CPU
flag register.

 d. De-initializing
 -----------------

If no further int10 calls are required for a certain chipset
the driver should call:

  void xf86FreeInt10(xf86Int10InfoPtr pInt);

to free the memory allocated for real mode int10 calls.


2. Porting issues
=================

The int10 real mode executor is  designed to run on top of various x86
CPU emulators as well as in vm86  mode of a real x86 CPU. If used with
a CPU  emulator the emulator and  CPU specific interfaces  can be held
separate thus  requiring minimal efforts  to port the int10  module to
new  platforms.   Currently  an  interface  to the  x86emu  real  mode
emulator is  provided.  Since  details of setting  up and  running the
vm86  mode   is  platform   dependent  both  the   platform  dependent
environment and the emulation layer  have to be ported. Several helper
functions are provided for that.

A CPU emulator should meet certain requirements to be usable
for the INT10 executor:

1. It must trap  calls to intXX instructions and  pass execution to an
   external  function  which  is   allowed  to  modify  CPU  registers
   including  the instruction  pointer  (IP) before  returning to  the
   emulator for  continuing execution.  When the external  function is
   called the  IP must point to  the instruction past  the intXX call.

2. The  emulator should  use externally  provided functions  to handle
   PIO.

3.  The emulator  should be able to use  externally provided functions
 to access memory  from the real mode memory  environment.  Note, that
 the  vm86  mode  usually  requires  one hunk  of  consecutive  memory
 starting at address  0 in the process virtual  memory space.  Thus if
 this mode is to be used, the OS environment has to be able to provide
 that, ie. it must be able to remap the processes virtual memory space
 onto itself.  If the emulator is able to handle memory access through
 externally  provided functions the  real mode  process memory  can be
 located anywhere  in the processes  virtual memory. It does  not even
 have to be consecutive.

4. The executor should terminate on encountering a 'hlt' instruction.


Functions to implement:

To simplify development  the code has been split  into a general setup
part and an emulator specific one. A generic setup code is provided in
generic.c.  It  should be  usable  with  any  emulator satisfying  the
conditions mentioned  above. Therefore the following  section on int10
setup may be skipped when porting int10 to new emulator.

If the  vm86() is to be used  no memory access functions  can be used.
Therefore the layout of the real mode memory image has to meet certain
requirements. Therefore  when porting to  other platforms a  new setup
code may  have to  be designed, too.  The following section  will give
guidelines how  this may be  done. A sample implementation  using SysV
IPC to  map the  appropriate real  mode memory image  to address  0 in
virtual  address  space  just  prior  to execution  may  be  found  in
xfree86/os-support/linux/int10/linux.c.

On  non-PC like  platforms emulation  of certain  PC features  such as
initialization of  BIOS int vectors, sys_BIOS constants  or PCI config
method 1 can be turned on by defining _PC.

I. Setup Code
-------------

This sets  up the real mode  memory image, calls the  emulator to POST
the chipset if required and  maintains memory allocations in real mode
address space.

1. xf86Int10InfoPtr xf86InitInt10(int entityIndex);

This  function should  first find  the screen  assigned to  the entity
carrying entitiyIndex and then call

       Bool int10skip(ScrnInfoPtr pScrn)

to find out if the user  has requested not to initialize int10.  If so
xf86InitInt10()  should  return  NULL. Otherwise  an  xf86Int10InfoRec
should be allocated.  This structure contains the following fields:

    a. int entityIndex   - index of the entity whose BIOS is to be 
                           executed.
    b. int scrnIndex     - index of the screen assigned the entity.
    c. pointer cpuRegs   - pointer to a emulator/vm86-mode private 
                           structure.  May hold cpu register values 
                           for the emulator.
    d. CARD16 BIOSseg    - Video BIOS segment address.
    e. pointer private   - pointer to a os specific data structure.
    f. struct _int10Mem* - pointer to a structure to hold the memory
                           access functions for use by an emulator.
    g. int num           - number of the int to be called.
    h. int ax..es,flags  - CPU register values to pass to int-call.

The Init  function should initialize  a-f. To initialize  the emulator
specific execute environment the function

     Bool xf86Int10ExecSetup(xf86Int10InfoPtr pInt)

should be called. If this function returns FALSE any already allocated
memory should be freed and xf86Int10Init(0 should exit returning NULL.

If the  platform has  a PC  like system BIOS  it may  be copied  to or
mapped into memory  locations SYS_BIOS to SYS_SIZE-1 of  the real mode
memory environment of this process. Otherwise the helper function: 

int setup_system_bios(CARD32 base_addr); 

may be  called to set  up a rudimentary  system BIOS sufficient  to be
used to  boot video BIOSes.   base_addr specifies the  virtual address
corresponding to SYS_BIOS in the  real mode environment.  If a PC-like
int vector and BIOS data area is available it should be copied to 0 to
LOW_PAGE_SIZE of the entities real mode environment.  In this case the
video interrupt  related entries should  be reset for  all non-primary
cards by calling:

void reset_int_vect(xf86Int10InfoPtr pInt); To initialize the

correct video BIOS  entry points the BIOS must  be warm-booted.  If no
PC-like int vector is available one can be set up by calling 

void setup_int_vect(xf86Int10InfoPtr pInt); 

In this  case the  video BIOS  has to be  warm-booted always.   If the
video BIOS  for this entity has  been installed during boot  it may be
mapped (or  copied) directly to the  correct address in  the real mode
memory environment.  Otherwise

int mapPciRom(xf86Int10InfoPtr pInt, unsigned char * address); 

should  be called  to copy  the BIOS  image from  PCI  ROM.  'address'
specifies the address this image should be copied to. Sufficient space
to  hold an entire  BIOS image  should be  allocated prior  to calling
mapPciRom(). This function  will return the size of  the BIOS image in
bytes  if  it   was  able  to  successfully  copy   the  image  and  0
otherwise. To create a well defined point to exit the softbooter

void set_return_trap(xf86Int10Ptr pInt); 

may be called.  It sets up a 'hlt' instruction  in the emulator memory
just above the BIOS variable area. Before entering real mode execution
this address will be pushed onto  the return stack.  If the BIOS needs
to be  warm-booted this should be done  before leaving xf86InitInt10()
by setting num in the xf86Int10InfoRec to 0xe6 and calling

void xf86ExecX86int10(xf86Int10IfoPtr pInt); 

The  implementation of this  function will  be discussed  below.  This
function  should be  wrapped  by calls  to void  LockLegacyVGA(screen,
legacyVGAPtr vga); and void UnlockLegacyVGA(screen, legacyVGAPtr vga);
The struct  vga is  used to hold  the state  of the legacy  VGA access
registers  if  a legacy  VGA  device  exists.  xf86InitInt10()  should
return a pointer to the xf86Int10InfoRec allocated.

2. Bool MapCurrentInt10(xf86Int10InfoPtr pInt);

In case  a platform specific  mapping has to  be performed to  map the
memory allocated for the real  mode memory environment into a specific
location prior to executing the x86 real mode code a function

        Bool MapCurrentInt10(xf86Int10InfoPtr pInt);

has to  be provided. It will  be called by a  helper function whenever
the active entity changes. If the  vm86 mode is used it is most likely
that the 1MB real mode memory space located somewhere in the processes
virtual memory  will have to be  remapped to address 0  of the virtual
memory space.

3.   void xf86FreeInt10(xf86Int10InfoPtr pInt);

To free all memory allocated for video BIOS calls of a specific entity
the function

       void xf86FreeInt10(xf86Int10InfoPtr pInt);

should  be  provided.  If  the  entity  to  be  freed  was  mapped  by
MapCurrentInt10() this mapping needs to be undone also.

4. 
   void * xf86Int10AllocPages(xf86Int10InfoPtr pInt,int num, int *off)
   void xf86Int10FreePages(xf86Int10InfoPtr pInt, void *pbase, int num)

xf86Int10AllocPages()  should  allocate  'num'  consecutive  page-size
chunks of memory. In real mode memory space this range needs to occupy
consecutive addresses,  too. The function  must return the  address of
this memory.  The offset in real  mode memory needs to  be returned in
'off'. If  no block of 'num'  pages are available  the function should
return NULL.

xf86Int10FreePages() will  free the  'num' pages starting  at 'pbase'.
'num'  is  equal  to  the  number  of  pages  allocated  by  a  single
xf86Int10AllocatePages()  call. 'pbase'  is the  address of  the range
previously returned by xf86Int10AllocatePages().

II. Emulator specific functions
-------------------------------

1. Bool xf86Int10ExecSetup(xf86Int10InfoPtr pInt);

This function will  be called from xf86InitInt10(). It  may be used to
set  up   the  static  emulator   specific  part  of  the   real  mode
environment. On success it should return TRUE.

2. xf86ExecX86int10(xf86Int10InfoPtr pInt);

This function  gets called  to execute  an int call.  It may  call the
helper function:

       void setup_int(xf86Int10InfoPrt pInt);

to copy the register values  to the emulator specific locations and to
set up the non-static real mode execution environment.  On return from
setup_int()   'Int10Current'   holds   a   pointer  to   the   current
xf86Int10InfoRec.

It should start execution by calling 

       Bool int_handler(xf86Int10InfoPtr pInt);

and if this function returns TRUE it should call whatever necessary to
continue execution until a  'hlt' instruction is encountered.  To copy
the resulting register values back to the xf86Int10InfoRec structure

     void finish_int(xf86Int10InfoPtr pInt);

should be called. 

Helper  functions are  provided to  aid the  implementation of  a vm86
call:

  Bool vm86_GP_fault(xf86Int10InfoPtr pInt);

This  function  handles  instructions  which  cause  a  vm86  call  to
trap.  PIO  access  is handled  by  the  in/out  calls as  defined  in
compiler.h. Optionally the PIO  instructions can be logged by defining
PRINT_PORT in xf86int10.h. This is meant for debugging purposes.

Unknown  instructions  and   'hlt'  cause  vm86_GP_fault()  to  return
FALSE. Otherwise TRUE is returned.

Note: This  function is  currently based on  the Linux vm86  call.  It
might have  to be modified  or even rewritten  for other OS.   So your
mileage may vary.

Functions to dump memory, code, xf86 CPU register values and stack are
also provided.  Take a  look at  helper.c To view  a memory  range the
function

    void dprint(unsigned long start, unsigned long size)

is provided. The use should be self explanatory.

Register  and memory  access functions  are provided  in helper_mem.c.
The PIO register access functions  can trap access to PCI config space
access register (config method 1) if _PC is not defined.

A header  file 'defines.h' is required to  define OS/emulator specific
ways  to access  memory and  xf86 CPU  registers: Defines  need  to be
provided     for    memory     byte/work/long     read/write    access
(MEM_RB(name,addr),MEM_RW(name,addr),MEM_RL(name,addr),
MEM_WB(name,addr,val),MEM_WL(name,addr,val),MEM_WL(name,addr,val))   of
the real mode memory environment. 'name' will contain a pointer to the
current   xf86Int10InfoRec.  Currently   defines  are   available  for
vm86-mode under  Linux and x86emu.  They may be activated  by defining
_X86EMU or _VM86_LINUX respectively.

Note: Emulators usually are not able to pass this pointer when calling
memory  access functions.  In this  case a  global variable  should be
defined  which can  hold this  pointer. This  variable can  be  set in
MapCurrentInt10().  It also  must be  set in  xf86InitInt10()  if this
function  calls the  memory  access functions  either  directly or  by
calling  xf86ExecX86int10(pInt).   Defines   to  access  the  emulator
specific   xf86   CPU    register   locations   are   also   required:
X86_EAX,...,X86_EFLAGS  for  access  of  the full  32  bit  registers,
X86_AX...X86_FLAGS   for  access   of   the  16   bit  registers   and
XF86_AL,XF86_BL,XF86_CL,XF86_DL  to  access  the  lower  byte  of  the
AX,BX,CX and DX register.


$XFree86: xc/programs/Xserver/hw/xfree86/int10/INT10.HOWTO,v 1.2 2000/02/08 13:13:22 eich Exp $