layout
\layout Standard
-The 8051 family of micro controller have a minimum of 128 bytes of internal
- memory which is structured as follows
+The 8051 family of microcontrollers have a minimum of 128 bytes of internal
+ RAM memory which is structured as follows
\newline
\newline
-- Bytes 00-1F - 32 bytes to hold up to 4 banks of the registers R7 to R7
+- Bytes 00-1F - 32 bytes to hold up to 4 banks of the registers R0 to R7,
\newline
-- Bytes 20-2F - 16 bytes to hold 128 bit variables and
+- Bytes 20-2F - 16 bytes to hold 128 bit variables and,
\newline
- Bytes 30-7F - 60 bytes for general purpose use.
\newline
-\newline
-Normally the SDCC compiler will only utilise the first bank
+\layout Standard
+
+Adittionally some members of the MCS51 family may have up to 128 bytes of
+ additional, indirectly addressable, internal RAM memory (
+\emph on
+idata
+\emph default
+).
+ Furtermore, some chips may have some built in external memory (
+\emph on
+xdata
+\emph default
+) which should not be confused with the internal, direclty addressable RAM
+ memory (
+\emph on
+data
+\emph default
+).
+ Usually this built in
+\emph on
+xdata
+\emph default
+ memory has to be activated before using it (you can probably find this
+ information on the datasheet of the microcontroller your are using).
+\layout Standard
+
+Normally SDCC will only use the first bank
\begin_inset LatexCommand \index{bank}
\end_inset
- of registers, but it is possible to specify that other banks of registers
- should be used in interrupt
+ of registers (register bank 0), but it is possible to specify that other
+ banks of registers should be used in interrupt
\begin_inset LatexCommand \index{interrupt}
\end_inset
routines.
- By default, the compiler will place the stack after the last bank of used
- registers, i.e.
- if the first 2 banks of registers are used, it will position the base of
- the internal stack at address 16 (0X10).
+ By default, the compiler will place the stack after the last byte of allocated
+ memory for variables.
+ For example, if the first 2 banks of registers are used, and only four
+ bytes are used for
+\emph on
+data
+\emph default
+ variables, it will position the base of the internal stack at address 20
+ (0x14).
This implies that as the stack
\begin_inset LatexCommand \index{stack}
grows, it will use up the remaining register banks, and the 16 bytes used
by the 128 bit variables, and 60 bytes for general purpose use.
-\layout Standard
-
-By default, the compiler uses the 60 general purpose bytes to hold "near
- data".
- The compiler/optimiser may also declare some Local Variables in this area
- to hold local data.
-
-\layout Standard
-
-If any of the 128 bit variables are used, or near data is being used then
- care needs to be taken to ensure that the stack does not grow so much that
- it starts to over write either your bit variables or "near data".
- There is no runtime checking to prevent this from happening.
-\layout Standard
-
-The amount of stack being used is affected by the use of the "internal stack"
- to save registers before a subroutine call is made (-
+ If any bit variables are used, the data variables will be placed after
+ the byte holding the last bit variable.
+ For example, if register banks 0 and 1 are used, and there are 9 bit variables
+ (two bytes used),
+\emph on
+data
+\emph default
+ variables will be placed starting at address 0x22.
+ You can also use -
\begin_inset ERT
status Collapsed
/
\end_inset
--stack-auto
-\begin_inset LatexCommand \index{-\/-stack-auto}
+-data-loc
+\begin_inset LatexCommand \index{-\/-data-loc}
\end_inset
- will declare parameters and local variables on the stack) and the number
- of nested subroutines.
-\layout Standard
-
-If you detect that the stack is over writing you data, then the following
- can be done.
- -
+ to specify the start address of the
+\emph on
+data
+\emph default
+ and -
\begin_inset ERT
status Collapsed
/
\end_inset
--xstack will cause an external stack to be used for saving registers and
- (if -
+-iram-size to specify the size of the total internal RAM (
+\emph on
+data
+\emph default
++
+\emph on
+idata
+\emph default
+).
+
+\layout Standard
+
+By default the 8051 linker will place the stack after the last byte of data
+ variables.
+ Option -
\begin_inset ERT
status Collapsed
/
\end_inset
--stack-auto is being used) storing parameters and local variables.
- However this will produce more code which will be slower to execute.
-
-\layout Standard
+-stack-loc
+\begin_inset LatexCommand \index{-\/-stack-loc}
--
+\end_inset
+
+ allows you to specify the start of the stack, i.e.
+ you could start it after any data in the general purpose area.
+ If your microcontroller has aditional indirectly addressable internal RAM
+ (
+\emph on
+idata
+\emph default
+) you can place the stack on it.
+ You may also need to use -
\begin_inset ERT
status Collapsed
/
\end_inset
--stack-loc
-\begin_inset LatexCommand \index{-\/-stack-loc}
+-xdata-loc
+\begin_inset LatexCommand \index{-\/-data-loc}
\end_inset
- will allow you specify the start of the stack, i.e.
- you could start it after any data in the general purpose area.
- However this may waste the memory not used by the register banks and if
- the size of the "near data" increases, it may creep into the bottom of
- the stack.
-\layout Standard
-
--
+ to set the start address of the external RAM (
+\emph on
+xdata
+\emph default
+) and -
\begin_inset ERT
status Collapsed
/
\end_inset
--data-loc
+-xram-size
\begin_inset LatexCommand \index{-\/-data-loc}
\end_inset
- allows you to specify the start address of the near data.
- This could be used to move the "near data" further away from the stack
- giving it more room to grow.
- This will only work if no bit variables are being used and the stack can
- grow to use the bit variable space.
-\newline
-
-\newline
-Conclusion.
-\newline
-
-\newline
-If you find that the stack is over writing your bit variables or "near data"
- then the approach which best utilised the internal memory is to position
- the "near data" after the last bank of used registers or, if you use bit
- variables, after the last bit variable by using the -
+ to specify its size.
+ Same goes for the code memory, using -
\begin_inset ERT
status Collapsed
/
\end_inset
--data-loc, e.g.
- if two register banks are being used and no bit variables, -
+-code-loc
+\begin_inset LatexCommand \index{-\/-data-loc}
+
+\end_inset
+
+ and -
\begin_inset ERT
status Collapsed
/
\end_inset
--data-loc 16.
-\layout Standard
+-code-size
+\begin_inset LatexCommand \index{-\/-data-loc}
-If bit variables are being used, another method would be to try and squeeze
- the data area in the unused register banks if it will fit, and start the
- stack after the last bit variable.
+\end_inset
+
+.
+ If in doubt, don't specify any options and see if the resulting memory
+ layout is appropiate, then you can twik it.
+\layout Standard
+
+The 8051 linker generates two files with memory allocation information.
+ The first, with extension .map shows all the variables and segments.
+ The second with extension .mem shows the final memory layout.
+ The linker will complaint either if memory segments overlap, there is not
+ enough memory, or there is not enough space for stack.
+ If you get any linking warnings and/or errors related to stack or segments
+ allocation, take a look at either the .map or .mem files to find out what
+ the problem is.
+ The .mem file may even suggest a solution to the problem.
\layout Subsection
Tools
\begin_inset Tabular
-<lyxtabular version="3" rows="9" columns="3">
+<lyxtabular version="3" rows="12" columns="3">
<features>
<column alignment="center" valignment="top" leftline="true" width="0pt">
<column alignment="center" valignment="top" leftline="true" width="0pt">
\layout Standard
+aslink
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\layout Standard
+Linker
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\layout Standard
+
+\family roman
+\series medium
+\shape up
+\size normal
+\emph off
+\bar no
+\noun off
+\color none
+sdcc/bin
+\end_inset
+</cell>
+</row>
+<row topline="true" bottomline="true">
+<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
+\begin_inset Text
+
+\layout Standard
+
+link-z80
+\end_inset
+</cell>
+<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
+\begin_inset Text
+
+\layout Standard
+
+Linker
+\end_inset
+</cell>
+<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
+\begin_inset Text
+
+\layout Standard
+
+
+\family roman
+\series medium
+\shape up
+\size normal
+\emph off
+\bar no
+\noun off
+\color none
+sdcc/bin
+\end_inset
+</cell>
+</row>
+<row topline="true" bottomline="true">
+<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
+\begin_inset Text
+
+\layout Standard
+
+link-gbz80
+\end_inset
+</cell>
+<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
+\begin_inset Text
+
+\layout Standard
+
+Linker
+\end_inset
+</cell>
+<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
+\begin_inset Text
+
+\layout Standard
+
+
+\family roman
+\series medium
+\shape up
+\size normal
+\emph off
+\bar no
+\noun off
+\color none
+sdcc/bin
+\end_inset
+</cell>
+</row>
+<row topline="true" bottomline="true">
+<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
+\begin_inset Text
+
+\layout Standard
+
+packihx
+\end_inset
+</cell>
+<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
+\begin_inset Text
+
+\layout Standard
+
+ihx packer
+\end_inset
+</cell>
+<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
+\begin_inset Text
+
+\layout Standard
+
+
+\family roman
+\series medium
+\shape up
+\size normal
+\emph off
+\bar no
+\noun off
+\color none
+sdcc/bin
\end_inset
</cell>
</row>
projects / fw / sdcc / commitdiff