Cortex-M1 TCM initialization in the ARM Cortex-M1 FPGA Development Kit Altera Edition
Application Note 213
Release information
Change history
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Date
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Issue
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Change
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September 2008
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A
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First release
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The ARM Cortex-M1 processor has optional,
configurable Tightly Coupled Memories (TCMs) for instructions and data.
Highest performance is achieved when code is run from the TCMs, and you can
also pre-initialize the TCMs when the processor is synthesized so that they
contain known data when the device is powered on.
This Application Note describes how you can
initialize the processor TCMs in the Cortex-M1 FPGA Development Kit, Altera
Cyclone III Edition. It also shows how to convert the memory images that are
produced by RealView MDK into a format that is suitable for Altera’s Quartus II
toolchain. The same technique also applies to other on-chip memories that you
may have in your ARM Cortex-M1 based system.
This Application Note assumes that you are
familiar with the Altera Quartus II toolchain and Keil RealView MDK software.
It applies to the following software versions:
·
ARM Cortex-M1 FPGA Development Kit version 1.1
·
Keil RealView MDK version 3.22a
·
Altera Quartus II version 8.0
You should refer to the documentation for
each tool for information about how to use the software. You may also refer to
the ARM Cortex-M1 FPGA Development Kit Cortex-M1 User Guide for more
information about the ARM Cortex-M1 processor in the ARM Cortex-M1 FPGA
Development Kit.
The ARM Cortex-M1 processor loads the
exception vector table from memory address 0x00000000 at reset. The vector table must be initialized with pointers to
the exception handlers in your software before the processor comes out of
reset.
When it is enabled, the Instruction Tightly
Coupled Memory (ITCM) starts at 0x00000000 in the processor’s memory map. The vector table will therefore
reside in the ITCM when the ITCM is present.
You should initialize the ITCM so that it
contains at least an initialized vector table. You may also decide to
initialize the ITCM with your entire software image because the ARM Cortex-M1
processor can achieve better performance when it is executing code from the
TCMs. If you only initialize the vector table, then you must ensure that other
memory in your system is initialized to contain startup code.
If you configured the processor to have no
ITCM then you must ensure that some external memory is available at address 0x00000000 and that this is initialized
to contain a vector table.
The following sections summarize some of
the instruction memory initialization techniques that you can use with your
software.
2.1.1
Initializing the ITCM with the entire software
image
If your code fits inside the ITCM then you
can initialize the ITCM with the vector table and the entire software image.
When the processor is reset the ITCM will already be initialized and the
processor will start to execute the software immediately. This method has
several advantages:
·
no boot loaders are required;
·
highest performance is achieved when executing
from TCMs.
However, you would need to re-synthesize
the system to change the contents of the ITCM.
Note
On-chip memories, such as those used for the ARM
Cortex-M1 TCMs, are initialized during the FPGA’s configuration phase. This is
typically when the device is powered on or when a new image is programmed using
a download cable. Resetting the processor does not reset the on-chip memories,
so you must ensure that software running on the processor does not accidentally
overwrite the instruction code or else the software might not work correctly
when the processor is reset. You can configure the processor to have a
read-only ITCM to protect against this.
2.1.2
Initializing the ITCM with vectors and using boot
code
You can initialize the ITCM with initial vectors
pointing to code in external memory that copies the software image into the
ITCM before executing it. Once the software image has been copied to the ITCM,
the bootloader can either branch to the ITCM code or, after updating the
vectors, request a reset.
The biggest advantage of this technique is
that the software can be changed without re-synthesizing the processor.
If you use the boot loader method, you
should ensure that:
·
the processor has been configured to have a
read/write ITCM so that the boot loader can modify the contents of the ITCM;
·
your boot code includes appropriate handlers for
exceptions that may occur while executing the boot code, for example Non-Maskable
Interrupt, HardFault and any exceptions that your boot code enables;
·
your boot code updates the ITCM vectors to their
application run-time values;
·
your external memory has been initialized with the
software image and boot code.
You can also initialize the Data Tightly
Coupled Memory (DTCM) if your startup code requires initialized data.
The Keil RealView MDK software uses the ARM
RealView Compiler Tools to generate images in AXF format, but there is also an
option to produce a Hex image in the Intel Hexadecimal format. The Intel
Hexadecimal format for memory images can be read by many memory programmers.
RealView MDK uses the fromelf
utility in the ARM RealView Compiler Tools to generate the Intel Hexadecimal
image. You can also run fromelf manually to generate a variety of other
memory initialization image formats, and information about how to use this
utility is provided in the RealView MDK’s online help system.
The Altera Quartus II software uses a
variation of the Intel Hexadecimal image format which has a number of
differences. You cannot use the Intel Hexadecimal files that RealView MDK
produces to initialize on-chip memories, such as the ARM Cortex-M1 TCMs, using
Altera Quartus II. However, the ARM Cortex-M1 FPGA Development Kit includes a hex2hex
utility that you can use to convert the Intel Hexadecimal files into the
Altera Quartus II format.
The rest of this section describes how to
use the hex2hex memory image conversion utility and how you can
configure RealView MDK to call this utility automatically each time your
software is compiled.
The RealView MDK project Hex file must be
converted into the Altera Quartus II format before being used for TCM
initialization. If your RealView MDK project Hex file contains data for more
than one memory, you also need to extract the appropriate section for each
memory. The hex2hex utility can do this.
You should refer to Application Note
215: Converting memory initialization files in the ARM Cortex-M1 FPGA
Development Kit Altera Edition to learn how to use the hex2hex
utility. The following example shows a typical command line for creating an
ITCM initialization file. You can use a similar command line to create a DTCM
initialization file, if required.
hex2hex.bat --infile=input.hex --outfile=itcm.hex ‑‑saddr=0x00000000
‑‑osize=32K ‑‑oformat=hex ‑‑padding
This command:
·
reads input data from input.hex;
·
writes the output file to itcm.hex;
·
converts a 32KB data section starting at the
ITCM address 0x00000000 in input.hex;
·
pads any empty address space in the output file
with zeroes.
Note
You must modify the example command line to use the
correct input Hex file and ITCM configuration. Refer to the Application
Note 215: Converting memory initialization files in the ARM Cortex-M1 FPGA
Development Kit Altera Edition for information about the hex2hex
command-line options.
You can configure your RealView MDK software
projects so that the hex2hex utility is automatically executed every
time you compile your project. This will ensure that your initialization files
are always up-to-date with your RealView MDK project, and removes the need to
run the command manually each time the project is compiled. To set up this
process, follow the steps listed in the headings below.
3.2.1
Enable Hex file output
Open the options window for your RealView
MDK project and select the Output tab. Ensure that the Create HEX File option
is selected, as shown in Figure 1. This option causes
RealView MDK to generate an image in the Intel Hexadecimal format.
Figure 1 – MDK Output options window
The Intel Hexadecimal file is saved in the obj
subdirectory of your RealView MDK project when the project is compiled. The
filename matches the name supplied in the Name of Executable field in
the Output options tab, which is also shown in Figure 1, with the addition
of a .hex file extension.
3.2.2
Set up user program execution
In the User
tab of the project options window, enable the Run #1 option under the Run
User Program After Build/Rebuild section. Enter the following command in
the adjacent text box, all on the same line, as shown in Figure 2. You can adjust the arguments to hex2hex.bat
to suit your project.
C:\ARM\CortexM1_DevKit\Utilities\hex2hex.bat
‑‑infile=”#H” ‑‑outfile=”C:\MyProject\%H” ‑‑saddr=0x00000000
‑‑osize=32K ‑‑oformat=hex ‑‑padding
You might need to change the path to hex2hex.bat
depending on where you installed the ARM Cortex‑M1 FPGA Development Kit.
Figure 2 – MDK User options window
RealView MDK automatically translates the #H argument to the --infile option to the name of the
project’s Intel Hexadecimal file, including the complete path. The %H argument to the ‑‑outfile option is
translated into the name of the Intel Hexadecimal file without the path.
Therefore the example command above will save the output Hex file to the given
directory C:\MyProject using the same filename as the original Intel Hexadecimal file.
The #H and %H tokens
are two examples of Key Sequences which have special meanings in
RealView MDK commands. For a complete list of available Key Sequences, refer
to the RealView MDK online help by pressing the Help button in the
project options window.
If a second Hex file is required, for
example for DTCM initialization, you can enable the Run #2 option and
enter a similar command using hex2hex.
Press the OK button in the options
window to confirm the changes.
3.2.3
Compiling the project
When you build your RealView MDK project in
the normal way, the commands that you entered in the user programs section of
the project options window will be executed after the project’s Intel Hexadecimal
file has been generated.
Altera Quartus II uses Hex files to
initialize on-chip memories such as the ARM Cortex-M1 TCMs. These Hex files
are in the Altera Hexadecimal format and you need one Hex file for each memory
that you want to initialize.
You must ensure that each Hex file:
·
uses relative addresses, relative to the base
address of the memory;
·
uses word addressing;
·
has data records matching the word size of the memory.
Section 3 describes how Hex files meeting these
requirements can be generated using the ARM Cortex-M1 FPGA Development Kit hex2hex
utility.
In the ARM Cortex-M1 FPGA Development Kit,
you configure the processor TCM initialization options in the SOPC Builder
environment in the Altera Quartus II design software. Figure 3 shows the
configuration dialog that appears when you instantiate the ARM Cortex-M1
processor in SOPC Builder. You can also change the configuration options by
double-clicking on a processor that has already been instantiated in the SOPC
Builder design pane.
Figure 3 – ARM Cortex-M1 processor configuration window in Altera SOPC
Builder
To enable ITCM initialization:
·
tick the Initialize ITCM contents
check-box; and
·
enter the name of the memory initialization file
in the From file box.
Note
You can also use the ITCM Read-only option to prevent software running
on the processor from writing to the ITCM. This can be useful if you are
initializing the ITCM to include your entire software image and want to prevent
accidental corruption and be sure that the processor will use the intended code
after a reset. This only affects writes from the processor core; a debugger
attached to a debug version of the processor can always write to the ITCM.
Press Finish in the processor
configuration dialog to apply the changes. After configuring your entire SOPC
Builder system, you must generate it by pressing the Generate button in
the main SOPC Builder window. This will apply your configuration options and
generate the system RTL.
During synthesis the Quartus II software
will search your Quartus II project directory for memory initialization files.
You must copy all memory initialization files to the Quartus II project
directory, otherwise you will see synthesis warnings relating to missing files
and your initialization settings will not take effect.
If you want to simulate your design then
you will also need to copy the memory initialization files into your simulation
project directory.
You can now synthesize the Quartus II
project. The TCM initialization data will be included in the FPGA programming
file so the memories will be initialized when the FPGA is configured.
This Application Note refers to the
following ARM documentation:
·
ARM Cortex-M1 FPGA Development Kit Altera Cyclone
III Edition Cortex-M1 User Guide
(ARM DUI 0395)
·
Application Note 215: Converting memory
initialization files in the ARM Cortex‑M1 FPGA Development Kit Altera
Edition (ARM DAI 0215)
You can also refer to the following online
resources for further related documentation:
·
http://infocenter.arm.com for access to ARM documentation
·
http://www.altera.com for access to Altera documentation
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