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Added text from Erik Ivanenko <erik.ivanenko@utoronto.ca> describing

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transition from real to protected mode and modified the spacing.
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Joel Sherrill
1998-06-01 15:14:36 +00:00
parent 2785eab264
commit 3b0f7cc3a3
2 changed files with 152 additions and 124 deletions
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128
doc/supplements/i386/bsp.t
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@@ -23,11 +23,10 @@
@end ifinfo @end ifinfo
@section Introduction @section Introduction
An RTEMS Board Support Package (BSP) must be designed An RTEMS Board Support Package (BSP) must be designed to support a
to support a particular processor and target board combination. particular processor and target board combination. This chapter presents a
This chapter presents a discussion of i386 specific BSP issues. discussion of i386 specific BSP issues. For more information on developing
For more information on developing a BSP, refer to the chapter a BSP, refer to the chapter titled Board Support Packages in the RTEMS
titled Board Support Packages in the RTEMS
Applications User's Guide. Applications User's Guide.
@ifinfo @ifinfo
@@ -39,74 +38,89 @@ An RTEMS based application is initiated when the i386
processor is reset. When the i386 is reset, processor is reset. When the i386 is reset,
@itemize @bullet @itemize @bullet
@item The EAX register is set to indicate the results of the
processor's power-up self test. If the self-test was not
executed, the contents of this register are undefined.
Otherwise, a non-zero value indicates the processor is faulty
and a zero value indicates a successful self-test.
@item The DX register holds a component identifier and @item The EAX register is set to indicate the results of the processor's
revision level. DH contains 3 to indicate an i386 component and power-up self test. If the self-test was not executed, the contents of
DL contains a unique revision level indicator. this register are undefined. Otherwise, a non-zero value indicates the
processor is faulty and a zero value indicates a successful self-test.
@item Control register zero (CR0) is set such that the @item The DX register holds a component identifier and revision level. DH
processor is in real mode with paging disabled. Other portions contains 3 to indicate an i386 component and DL contains a unique revision
of CR0 are used to indicate the presence of a numeric level indicator.
coprocessor.
@item All bits in the extended flags register (EFLAG) which @item Control register zero (CR0) is set such that the processor is in real
are not permanently set are cleared. This inhibits all maskable mode with paging disabled. Other portions of CR0 are used to indicate the
interrupts. presence of a numeric coprocessor.
@item The Interrupt Descriptor Register (IDTR) is set to point @item All bits in the extended flags register (EFLAG) which are not
at address zero. permanently set are cleared. This inhibits all maskable interrupts.
@item The Interrupt Descriptor Register (IDTR) is set to point at address
zero.
@item All segment registers are set to zero. @item All segment registers are set to zero.
@item The instruction pointer is set to 0x0000FFF0. The @item The instruction pointer is set to 0x0000FFF0. The first instruction
first instruction executed after a reset is actually at executed after a reset is actually at 0xFFFFFFF0 because the i386 asserts
0xFFFFFFF0 because the i386 asserts the upper twelve address the upper twelve address until the first intersegment (FAR) JMP or CALL
until the first intersegment (FAR) JMP or CALL instruction. instruction. When a JMP or CALL is executed, the upper twelve address
When a JMP or CALL is executed, the upper twelve address lines lines are lowered and the processor begins executing in the first megabyte
are lowered and the processor begins executing in the first of memory. @end itemize
megabyte of memory.
@end itemize
Typically, an intersegment JMP to the application's Typically, an intersegment JMP to the application's initialization code is
initialization code is placed at address 0xFFFFFFF0. placed at address 0xFFFFFFF0.
@ifinfo @ifinfo
@node Board Support Packages Processor Initialization, Processor Dependent Information Table, Board Support Packages System Reset, Board Support Packages @node Board Support Packages Processor Initialization, Processor Dependent Information Table, Board Support Packages System Reset, Board Support Packages
@end ifinfo @end ifinfo
@section Processor Initialization @section Processor Initialization
This initialization code is responsible for This initialization code is responsible for initializing all data
initializing all data structures required by the i386 in structures required by the i386 in protected mode and for actually entering
protected mode and for actually entering protected mode. The protected mode. The i386 must be placed in protected mode and the segment
i386 must be placed in protected mode and the segment registers registers and associated selectors must be initialized before the
and associated selectors must be initialized before the
initialize_executive directive is invoked. initialize_executive directive is invoked.
The initialization code is responsible for The initialization code is responsible for initializing the Global
initializing the Global Descriptor Table such that the i386 is Descriptor Table such that the i386 is in the thirty-two bit flat memory
in the thirty-two bit flat memory model with paging disabled. model with paging disabled. In this mode, the i386 automatically converts
In this mode, the i386 automatically converts every address from every address from a logical to a physical address each time it is used.
a logical to a physical address each time it is used. For more For more information on the memory model used by RTEMS, please refer to the
information on the memory model used by RTEMS, please refer to Memory Model chapter in this document.
the Memory Model chapter in this document.
If the application requires that the IDTR be some Since the processor is in real mode upon reset, the processor must be
value besides zero, then it should set it to the required value switched to protected mode before RTEMS can execute. Before switching to
at this point. All tasks share the same i386 IDTR value. protected mode, at least one descriptor table and two descriptors must be
Because interrupts are enabled automatically by RTEMS as part of created. Descriptors are needed for a code segment and a data segment. (
the initialize_executive directive, the IDTR MUST be set This will give you the flat memory model.) The stack can be placed in a
properly before this directive is invoked to insure correct normal read/write data segment, so no descriptor for the stack is needed.
interrupt vectoring. If processor caching is to be utilized, Before the GDT can be used, the base address and limit must be loaded into
then it should be enabled during the reset application the GDTR register using an LGDT instruction.
initialization code. The reset code which is executed before
the call to initialize_executive has the following requirements:
For more information regarding the i386s data If the hardware allows an NMI to be generated, you need to create the IDT
structures and their contents, refer to Intel's 386 and a gate for the NMI interrupt handler. Before the IDT can be used, the
Programmer's Reference Manual. base address and limit for the idt must be loaded into the IDTR register
using an LIDT instruction.
Protected mode is entered by setting thye PE bit in the CR0 register.
Either a LMSW or MOV CR0 instruction may be used to set this bit. Because
the processor overlaps the interpretation of several instructions, it is
necessary to discard the instructions from the read-ahead cache. A JMP
instruction immediately after the LMSW changes the flow and empties the
processor if intructions which have been pre-fetched and/or decoded. At
this point, the processor is in protected mode and begins to perform
protected mode application initialization.
If the application requires that the IDTR be some value besides zero, then
it should set it to the required value at this point. All tasks share the
same i386 IDTR value. Because interrupts are enabled automatically by
RTEMS as part of the initialize_executive directive, the IDTR MUST be set
properly before this directive is invoked to insure correct interrupt
vectoring. If processor caching is to be utilized, then it should be
enabled during the reset application initialization code. The reset code
which is executed before the call to initialize_executive has the following
requirements:
For more information regarding the i386s data structures and their
contents, refer to Intel's 386 Programmer's Reference Manual.

128
doc/supplements/i386/bsp.texi
View File

@@ -23,11 +23,10 @@
@end ifinfo @end ifinfo
@section Introduction @section Introduction
An RTEMS Board Support Package (BSP) must be designed An RTEMS Board Support Package (BSP) must be designed to support a
to support a particular processor and target board combination. particular processor and target board combination. This chapter presents a
This chapter presents a discussion of i386 specific BSP issues. discussion of i386 specific BSP issues. For more information on developing
For more information on developing a BSP, refer to the chapter a BSP, refer to the chapter titled Board Support Packages in the RTEMS
titled Board Support Packages in the RTEMS
Applications User's Guide. Applications User's Guide.
@ifinfo @ifinfo
@@ -39,74 +38,89 @@ An RTEMS based application is initiated when the i386
processor is reset. When the i386 is reset, processor is reset. When the i386 is reset,
@itemize @bullet @itemize @bullet
@item The EAX register is set to indicate the results of the
processor's power-up self test. If the self-test was not
executed, the contents of this register are undefined.
Otherwise, a non-zero value indicates the processor is faulty
and a zero value indicates a successful self-test.
@item The DX register holds a component identifier and @item The EAX register is set to indicate the results of the processor's
revision level. DH contains 3 to indicate an i386 component and power-up self test. If the self-test was not executed, the contents of
DL contains a unique revision level indicator. this register are undefined. Otherwise, a non-zero value indicates the
processor is faulty and a zero value indicates a successful self-test.
@item Control register zero (CR0) is set such that the @item The DX register holds a component identifier and revision level. DH
processor is in real mode with paging disabled. Other portions contains 3 to indicate an i386 component and DL contains a unique revision
of CR0 are used to indicate the presence of a numeric level indicator.
coprocessor.
@item All bits in the extended flags register (EFLAG) which @item Control register zero (CR0) is set such that the processor is in real
are not permanently set are cleared. This inhibits all maskable mode with paging disabled. Other portions of CR0 are used to indicate the
interrupts. presence of a numeric coprocessor.
@item The Interrupt Descriptor Register (IDTR) is set to point @item All bits in the extended flags register (EFLAG) which are not
at address zero. permanently set are cleared. This inhibits all maskable interrupts.
@item The Interrupt Descriptor Register (IDTR) is set to point at address
zero.
@item All segment registers are set to zero. @item All segment registers are set to zero.
@item The instruction pointer is set to 0x0000FFF0. The @item The instruction pointer is set to 0x0000FFF0. The first instruction
first instruction executed after a reset is actually at executed after a reset is actually at 0xFFFFFFF0 because the i386 asserts
0xFFFFFFF0 because the i386 asserts the upper twelve address the upper twelve address until the first intersegment (FAR) JMP or CALL
until the first intersegment (FAR) JMP or CALL instruction. instruction. When a JMP or CALL is executed, the upper twelve address
When a JMP or CALL is executed, the upper twelve address lines lines are lowered and the processor begins executing in the first megabyte
are lowered and the processor begins executing in the first of memory. @end itemize
megabyte of memory.
@end itemize
Typically, an intersegment JMP to the application's Typically, an intersegment JMP to the application's initialization code is
initialization code is placed at address 0xFFFFFFF0. placed at address 0xFFFFFFF0.
@ifinfo @ifinfo
@node Board Support Packages Processor Initialization, Processor Dependent Information Table, Board Support Packages System Reset, Board Support Packages @node Board Support Packages Processor Initialization, Processor Dependent Information Table, Board Support Packages System Reset, Board Support Packages
@end ifinfo @end ifinfo
@section Processor Initialization @section Processor Initialization
This initialization code is responsible for This initialization code is responsible for initializing all data
initializing all data structures required by the i386 in structures required by the i386 in protected mode and for actually entering
protected mode and for actually entering protected mode. The protected mode. The i386 must be placed in protected mode and the segment
i386 must be placed in protected mode and the segment registers registers and associated selectors must be initialized before the
and associated selectors must be initialized before the
initialize_executive directive is invoked. initialize_executive directive is invoked.
The initialization code is responsible for The initialization code is responsible for initializing the Global
initializing the Global Descriptor Table such that the i386 is Descriptor Table such that the i386 is in the thirty-two bit flat memory
in the thirty-two bit flat memory model with paging disabled. model with paging disabled. In this mode, the i386 automatically converts
In this mode, the i386 automatically converts every address from every address from a logical to a physical address each time it is used.
a logical to a physical address each time it is used. For more For more information on the memory model used by RTEMS, please refer to the
information on the memory model used by RTEMS, please refer to Memory Model chapter in this document.
the Memory Model chapter in this document.
If the application requires that the IDTR be some Since the processor is in real mode upon reset, the processor must be
value besides zero, then it should set it to the required value switched to protected mode before RTEMS can execute. Before switching to
at this point. All tasks share the same i386 IDTR value. protected mode, at least one descriptor table and two descriptors must be
Because interrupts are enabled automatically by RTEMS as part of created. Descriptors are needed for a code segment and a data segment. (
the initialize_executive directive, the IDTR MUST be set This will give you the flat memory model.) The stack can be placed in a
properly before this directive is invoked to insure correct normal read/write data segment, so no descriptor for the stack is needed.
interrupt vectoring. If processor caching is to be utilized, Before the GDT can be used, the base address and limit must be loaded into
then it should be enabled during the reset application the GDTR register using an LGDT instruction.
initialization code. The reset code which is executed before
the call to initialize_executive has the following requirements:
For more information regarding the i386s data If the hardware allows an NMI to be generated, you need to create the IDT
structures and their contents, refer to Intel's 386 and a gate for the NMI interrupt handler. Before the IDT can be used, the
Programmer's Reference Manual. base address and limit for the idt must be loaded into the IDTR register
using an LIDT instruction.
Protected mode is entered by setting thye PE bit in the CR0 register.
Either a LMSW or MOV CR0 instruction may be used to set this bit. Because
the processor overlaps the interpretation of several instructions, it is
necessary to discard the instructions from the read-ahead cache. A JMP
instruction immediately after the LMSW changes the flow and empties the
processor if intructions which have been pre-fetched and/or decoded. At
this point, the processor is in protected mode and begins to perform
protected mode application initialization.
If the application requires that the IDTR be some value besides zero, then
it should set it to the required value at this point. All tasks share the
same i386 IDTR value. Because interrupts are enabled automatically by
RTEMS as part of the initialize_executive directive, the IDTR MUST be set
properly before this directive is invoked to insure correct interrupt
vectoring. If processor caching is to be utilized, then it should be
enabled during the reset application initialization code. The reset code
which is executed before the call to initialize_executive has the following
requirements:
For more information regarding the i386s data structures and their
contents, refer to Intel's 386 Programmer's Reference Manual.