These are currently not used for the MCS51 port.
If you absolutely need them you can fall back to inline assembly or submit
a patch to SDCC.
+\end_layout
+
+\begin_layout Subsection
+Bankswitching
+\end_layout
+
+\begin_layout Standard
+Bankswitching
+\begin_inset LatexCommand \index{Bankswitching}
+
+\end_inset
+
+ (a.k.a.
+ code banking
+\begin_inset LatexCommand \index{code banking}
+
+\end_inset
+
+) is a technique to increase the code space above the 64k limit of the 8051.
+\end_layout
+
+\begin_layout Subsubsection
+Hardware
+\end_layout
+
+\begin_layout Standard
+\begin_inset Tabular
+<lyxtabular version="3" rows="3" columns="4">
+<features>
+<column alignment="center" valignment="top" width="0">
+<column alignment="center" valignment="top" leftline="true" width="0">
+<column alignment="center" valignment="top" leftline="true" width="0">
+<column alignment="center" valignment="top" leftline="true" rightline="true" width="0">
+<row topline="true" bottomline="true">
+<cell multicolumn="1" alignment="center" valignment="top" usebox="none">
+\begin_inset Text
+
+\begin_layout Standard
+\paragraph_spacing other 0.5
+8000-FFFF
+\end_layout
+
+\end_inset
+</cell>
+<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
+\begin_inset Text
+
+\begin_layout Standard
+bank 1
+\end_layout
+
+\end_inset
+</cell>
+<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
+\begin_inset Text
+
+\begin_layout Standard
+bank 2
+\end_layout
+
+\end_inset
+</cell>
+<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
+\begin_inset Text
+
+\begin_layout Standard
+bank 3
+\end_layout
+
+\end_inset
+</cell>
+</row>
+<row topline="true" bottomline="true">
+<cell multicolumn="1" alignment="center" valignment="top" usebox="none">
+\begin_inset Text
+
+\begin_layout Standard
+0000-7FFF
+\end_layout
+
+\end_inset
+</cell>
+<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
+\begin_inset Text
+
+\begin_layout Standard
+common
+\end_layout
+
+\end_inset
+</cell>
+<cell multicolumn="1" alignment="center" valignment="top" usebox="none">
+\begin_inset Text
+
+\begin_layout Standard
+
+\end_layout
+
+\end_inset
+</cell>
+<cell multicolumn="2" alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
+\begin_inset Text
+
+\begin_layout Standard
+
+\end_layout
+
+\end_inset
+</cell>
+</row>
+<row>
+<cell multicolumn="1" alignment="center" valignment="top" usebox="none">
+\begin_inset Text
+
+\begin_layout Standard
+SiLabs C8051F120 example
+\end_layout
+
+\end_inset
+</cell>
+<cell multicolumn="2" alignment="center" valignment="top" usebox="none">
+\begin_inset Text
+
+\begin_layout Standard
+
+\end_layout
+
+\end_inset
+</cell>
+<cell multicolumn="2" alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
+\begin_inset Text
+
+\begin_layout Standard
+
+\end_layout
+
+\end_inset
+</cell>
+<cell multicolumn="2" alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
+\begin_inset Text
+
+\begin_layout Standard
+
+\end_layout
+
+\end_inset
+</cell>
+</row>
+</lyxtabular>
+
+\end_inset
+
+
+\newline
+
+\newline
+Usually the hardware uses some sfr (an output port or an internal sfr) to
+ select a bank and put it in the banked area of the memory map.
+ Because the selected bank usually becomes active immediately you cannot
+ jump call directly from one bank to another and need to use a so-called
+ trampoline in the common area.
+ For SDCC an example trampoline is in crtbank.asm and you may need to change
+ it to your 8051 derivative or schematic.
+ The presented code is written for the C8051F120.
+\newline
+
+\newline
+When calling a banked function
+ SDCC will put the LSB of the functions address in register R0, the MSB
+ in R1 and the bank in R2 and then call this trampoline __sdcc_banked_call.
+ The current selected bank is saved on the stack, the new bank is selected
+ and an indirect jump is made.
+ When the banked function returns it jumps to __sdcc_banked_ret which restores
+ the previous bank and returns to the caller.
+\end_layout
+
+\begin_layout Subsubsection
+Software
+\end_layout
+
+\begin_layout Standard
+When writing banked software using SDCC you need to use some special keywords
+ and options.
+ You also need to take over a bit of work from the linker.
+\newline
+
+\newline
+To create a function
+ that can be called from another bank it requires the keyword banked.
+ The caller must see this in the prototype of the callee and the callee
+ needs it for a proper return.
+ Called functions within the same bank as the caller do not need the banked
+ keyword nor do functions in the common area.
+ Beware: SDCC does not know or check if functions are in the same bank.
+ This is your responsibility!
+\newline
+
+\newline
+Normally all functions you write end up in
+ the segment CSEG.
+ If you want a function explicitly to reside in the common area put it in
+ segment HOME.
+ This applies for instance to interrupt service routines as they should
+ not be banked.
+\end_layout
+
+\begin_layout Standard
+Functions that need to be in a switched bank must be put in a named segment.
+ The name can be mostly anything upto eight characters (e.g.
+ BANK1).
+ To do this you either use --codeseg BANK1 on the command line when compiling
+ or #pragma codeseg BANK1 at the top of the C source file.
+ The segment name always applies to the whole source file and generated
+ object so functions for different banks need to be defined in different
+ source files.
+\newline
+
+\newline
+When linking your objects you need to tell the linker where
+ to put your segments.
+ To do this you use the following command line option to SDCC: -Wl-b BANK1=0x180
+00.
+ This sets the virtual start address of this segment.
+ It sets the banknumber to 0x01 and maps the bank to 0x8000 and up.
+ The linker will not check for overflows, again this is your responsibility.
+\end_layout
+
+\begin_layout Standard
\begin_inset VSpace bigskip
\end_inset
projects / fw / sdcc / commitdiff