Document BIOS bytecode overriding.

Pointed out by: Alex Zepeda <zipzippy@sonic.net>
Reviewed by:	David Wolfskill <david@catwhisker.org>

share/man/man4/acpi.4

@@ -258,11 +258,43 @@ The object and all of its children will be ignored during the
 bus/children scan of the namespace.
 The ACPI CA code will still
 know about the avoided region.
+.Sh OVERRIDING YOUR BIOS BYTECODE
+ACPI interprets bytecode named AML, ACPI Machine Language, provided by the BIOS
+vendor as a memory image at boot time. Sometimes the AML code contains
+a problem that does not appeared in Microsoft implementation.
+So we provide a way to override it with your own AML code.
+.Pp
+In order to load your AML code, 
+you must edit 
+.Pa /boot/loader.conf
+and 
+include the following lines.
+.Bd -literal -offset indent
+acpi_dsdt_load="YES"
+acpi_dsdt_name="/boot/acpi_dsdt.aml" #You may change the name.
+.Ed
+.Pp
+In order to prepare your AML code, you will require
+.Xr acpidump 8 ,
+.Xr iasl 1
+in devel/acpicatools port, and some ACPI knowledge.
 .Sh COMPATIBILITY
 ACPI is only found/supported on Intel platforms (i386/IA32 and IA64).
 .Sh SEE ALSO
 .Xr config 8 ,
+.Xr loader.conf 5 ,
+.Xr acpidump 8 ,
 .Xr acpi 9
+.Rs
+.%A Compaq Computer Corporation
+.%A Intel Corporation
+.%A Microsoft Corporation
+.%A Phoenix Technologies Ltd.
+.%A Toshiba Corporation
+.%D July 27 2000
+.%T "Advanced Configuration and Power Interface Specification"
+.%O http://acpi.info/spec.htm
+.Re
 .Sh AUTHORS
 .An -nosplit
 The ACPI CA subsystem is developed and maintained by