System Initialization
Élan™SC520 Microcontroller User’s Manual
3-3
Some embedded systems execute from read-only memory (usually Flash) and only use
DRAM for data storage. This style of system architecture is supported by most RTOS
products. This is reflected in line 7. Systems that execute out of Flash memory do not need
to copy the operating system and/or application to DRAM.
Another interesting point is that once the DRAM controller is initialized, then the initialization
code can setup a stack and finish the reset of its work in a high-level language (usually C).
3.1.2
BIOS Initialization Sequence
In contrast to a native embedded system, the flow of system initialization with a BIOS
generally follows this sequence:
1
< Reset event >
2
Near Jump to reset handler from the reset vector
3
Map the Memory-Mapped Configuration Region (MMCR) to an address below
0010FFEFh (real-mode address limit)
4
Determine the cause of the reset
5
Initialize the DRAM controller and DRAM. Size the DRAM, record in CMOS
6
Copy the BIOS into DRAM (shadowing)
7
Execute a Far Jump within the BIOS code to start execution out of the
shadowed BIOS copy instead of the copy in ROM
8
Set up basic interrupt handlers for processor faults
9
Detect the CPU ID and display on the console
10
Set the processor speed
11
Configure the GP bus timings
12
Configure the pin multiplexing
13
Configure the GP bus chip selects
14
Configure the Programmable Address Region (PAR) registers
15
Configure the interrupt mappings
16
Configure the programmable I/O (PIO) pins
17
Configure the PCI bus controller and arbitration
18
Now, the BIOS can continue with standard PC-style system initialization
There are some important contrasts between the steps for a system with a PC BIOS and
those for a native embedded system.
■
Steps 1 through 6 are done in real mode while executing from the reset segment before
executing the first Far Jump (JMP) instruction. This is in contrast to the initialization for
a native embedded system, which transitions to simple protected mode before these
steps.
■
The Memory-Mapped Configuration Region (MMCR) needs to be mapped to a region
below 00100000h so it is accessible by real-mode software. 32-bit protected-mode
native embedded systems do not need to move the MMCR.
■
The remainder of the system initialization is done in real mode from the BIOS image
running from DRAM. This is in contrast to an embedded system, which does all of its
initialization from 32-bit protected mode (running either from DRAM or Flash).
3.1.3
Memory-Mapped Configuration Region (MMCR)
The Memory-Mapped Configuration Region (MMCR) is a 4-Kbyte area located at physical
address FFFEF000h and contains various configuration and control registers for the
ÉlanSC520 microcontroller. Configuring and controlling many of the device’s features
requires accessing the MMCR registers. System initialization code for a native embedded
system can access this region directly because most (or all) initialization takes place from
32-bit protected mode.
Содержание Elan SC520
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Страница 28: ...Introduction xxviii lan SC520 Microcontroller User s Manual...
Страница 42: ...Architectural Overview 1 14 lan SC520 Microcontroller User s Manual...
Страница 78: ...System Initialization 3 22 lan SC520 Microcontroller User s Manual...
Страница 108: ...Clock Generation and Control 5 10 lan SC520 Microcontroller User s Manual...
Страница 118: ...Reset Generation 6 10 lan SC520 Microcontroller User s Manual...
Страница 148: ...System Arbitration 8 24 lan SC520 Microcontroller User s Manual...
Страница 214: ...SDRAM Controller 10 36 lan SC520 Microcontroller User s Manual...
Страница 230: ...Write Buffer and Read Buffer 11 16 lan SC520 Microcontroller User s Manual...
Страница 288: ...GP Bus DMA Controller 14 22 lan SC520 Microcontroller User s Manual...
Страница 316: ...Programmable Interval Timer 16 8 lan SC520 Microcontroller User s Manual...
Страница 328: ...Software Timer 18 4 lan SC520 Microcontroller User s Manual...
Страница 346: ...Real Time Clock 20 12 lan SC520 Microcontroller User s Manual...
Страница 360: ...UART Serial Ports 21 14 lan SC520 Microcontroller User s Manual...
Страница 414: ...AMDebug Technology 26 8 lan SC520 Microcontroller User s Manual...