📄 armcc locate constants to fixed locations.htm

📁 LPC2214 Chip Protection
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content="QUESTION: I am using a Philips LPC2000 device. To read protect the chip, I want to locate a constant at a fixed memory location (0x1FC) in the Flash ROM. What is the best way to do this? ANSWER: To locate a constant at a fixed address you must create a small module that contains the constant, and...">
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      <H1>ARMCC: LOCATE CONSTANTS TO FIXED LOCATIONS</H1>
      <HR>

      <P>Information in this article applies to:</P>
      <UL>
        <LI>RealView C Compiler Version 3</LI></UL>
      <HR>

      <H3>QUESTION</H3>
      <P>I am using a Philips LPC2000 device. To read protect the chip, I want 
      to locate a constant at a fixed memory location (0x1FC) in the Flash 
      ROM.</P>
      <P>What is the best way to do this?</P>
      <H3>ANSWER</H3>
      <P>To locate a constant at a fixed address you must create a small module 
      that contains the constant, and modify the scatter file to reference that 
      module. Here are the steps:</P>
      <OL>
        <LI>
        <P>Write the following C module called <B>ABS_ADDRESS.C</B> to define 
        the constant:</P><PRE>#pragma push
#pragma Ono_remove_unused_constdata
unsigned int const Security_Value = 0x87654321;
#pragma pop
</PRE>
        <P>Make sure that you reduce optimization with:</P><PRE><STRONG>#pragma Ono_remove_unused_constdata</STRONG>
</PRE>
        <P>Without this directive, the linker could remove the constant from the 
        final object.</P>
        <LI>
        <P>Locate the project's scatter file. µVision creates a scatter file 
        (with the extension *.SCT) when the <B>Use Memory Layout from Target 
        Dialog</B> option (<B>Project — Options for Target — Linker</B>) is 
        checked. The scatter file looks like this:</P><PRE>LR_IROM1 0x00000000 0x00080000  {  ; load region
  ER_IROM1 0x00000000  {       ; load address = execution address
   *.o (RESET, +First)
   * (+RO)
  }
  RW_IRAM1 0x40000000 0x00008000  {  ; RW data
   * (+RW +ZI)
  }
}
</PRE>
        <LI>
        <P>Disable the <B>Use Memory Layout from Target Dialog</B> option, then 
        specify the scatter file under <B>Project — Options — Linker — Scatter 
        File</B> and change the content of this file to:</P><PRE>LR_IROM1 0x00000000 0x00080000 { ; load region
  ER_IROM1 0x00000000 { ; load address = execution address
    *.o (RESET, +First)
<STRONG>    .ANY (*)</STRONG>
  }

<STRONG>  ABS_ADDRESS 0x1FC FIXED 4 {
    abs_address.o (*)
  }

  ER_IROM2 +0 0x80000 {
    * (+RO)
    .ANY(*)
  }</STRONG>

  RW_IRAM1 0x40000000 0x00008000 { ; RW data
    * (+RW +ZI)
  }
}
</PRE></LI></OL>
      <P>This will locate the constant in the file ABS_ADDRESS.C to memory 
      location 0x1FC.</P>
      <P>The linker will still remove unused sections. To avoid that you need to 
      enter the directive <B>--keep abs_address.o(.constdata)</B> under 
      <B>Project — Options — Linker — Misc controls</B>.</P>
      <H3>MORE INFORMATION</H3>
      <UL>
        <LI>RealView Linker and Utilities User's Guide</LI></UL>
      <H3>FORUM THREADS</H3>
      <P>The following <A href="http://www.keil.com/forum/">Discussion Forum</A> 
      threads may provide information related to this topic.</P>
      <UL>
        <LI><A href="http://www.keil.com/forum/docs/thread10802.asp">Ading a 
        flash table</A>
        <LI><A href="http://www.keil.com/forum/docs/thread10579.asp">How can i 
        protect a program from write/erase?</A></LI></UL>
      <P class=TabNotes>Last Reviewed: Wednesday, November 15, 2006</P>
      <HR>

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