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165 lines
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HTML
165 lines
4.8 KiB
HTML
<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<title>2.7 C Library</title>
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<link type="text/css" rel="stylesheet" href="style.css">
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</head>
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<body>
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<h1>2.7: C Library</h1>
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So far I have used three Standard C library functions for output:
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<code>printf()</code>, <code>putchar()</code> and <code>puts()</code>. It’s
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time to bundle them as a library. This will give me more flexibility as I will
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not have to give a full list of the modules to link, the linker will handle
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the missing dependencies by looking into the libraries.
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<h2>puts()</h2>
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I have already packaged <code>printf()</code> and <code>putchar()</code> in
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stand alone modules. As I have removed my previous implementation of
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<code>puts()</code> from the system, I need to create puts.c.
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<pre>
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/* puts.c -- write a string to stdout */
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#include <stdio.h>
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#include "system.h" /* kputc(), kputs() */
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int puts( const char *s) {
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kputs( s) ;
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kputc( '\n') ;
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return 0 ;
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}
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</pre>
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<h2>Updating Makefile</h2>
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I need to tell <b>GNU make</b> how to manage and use the library, which
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means updating <b>Makefile</b>.
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<p>
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What’s the name, the content and the rule to maintain the library:
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<pre>
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AR = $(BINPFX)ar
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LIBOBJS = printf.o putchar.o puts.o
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LIBSTEM = stm32
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lib$(LIBSTEM).a: $(LIBOBJS)
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$(AR) rc $@ $?
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</pre>
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Where to look for and which libraries to use in the link phase:
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<pre>
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LIBS = -l$(LIBSTEM) -lgcc
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LIB_PATHS = -L. -L$(LIBDIR)
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$(PROJECT).elf: $(OBJS) lib$(LIBSTEM).a
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@echo $@ from $(OBJS)
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$(LD) -T$(LD_SCRIPT) $(LIB_PATHS) -Map=$(PROJECT).map -cref -o $@ $(OBJS) $(LIBS)
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$(SIZE) $@
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$(OBJDUMP) -hS $@ > $(PROJECT).lst
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</pre>
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Library modules are implicitly part of the composition, so it’s not
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necessary to list them anymore.
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<pre>
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#SRCS = startup.c uplow.2.c uptime.c printf.c putchar.c
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SRCS = startup.c uplow.2.c uptime.c
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</pre>
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I include libraries in the list of files to delete when doing a make
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clean.
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<pre>
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clean:
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@echo CLEAN
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@rm -f *.o *.elf *.map *.lst *.bin *.hex *.a
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</pre>
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<h2>Building uptime</h2>
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Build terminates successfully producing the same executable as before.
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<pre>
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$ make
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f030f4.elf from startup.o uplow.2.o uptime.o
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text data bss dec hex filename
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1797 0 12 1809 711 f030f4.elf
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f030f4.hex
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f030f4.bin
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</pre>
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Checking the map produced by the linker I can see that it fetched the
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necessary modules for <code>printf()</code> and <code>putchar()</code> from the
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newly created library.
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<pre>
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Archive member included to satisfy reference by file (symbol)
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.\libstm32.a(printf.o) uptime.o (printf)
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.\libstm32.a(putchar.o) uptime.o (putchar)
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D:/Program Files (x86)/GNU Arm Embedded Toolchain/arm-gnu-toolchain-13.3.rel1-mi
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ngw-w64-i686-arm-none-eabi/lib/gcc/arm-none-eabi/13.3.1/thumb/v6-m/nofp\libgcc.a
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(_thumb1_case_sqi.o)
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.\libstm32.a(printf.o) (__gnu_thumb1_case_sqi)
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D:/Program Files (x86)/GNU Arm Embedded Toolchain/arm-gnu-toolchain-13.3.rel1-mi
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ngw-w64-i686-arm-none-eabi/lib/gcc/arm-none-eabi/13.3.1/thumb/v6-m/nofp\libgcc.a
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(_udivsi3.o)
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uptime.o (__aeabi_uidiv)
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D:/Program Files (x86)/GNU Arm Embedded Toolchain/arm-gnu-toolchain-13.3.rel1-mi
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ngw-w64-i686-arm-none-eabi/lib/gcc/arm-none-eabi/13.3.1/thumb/v6-m/nofp\libgcc.a
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(_divsi3.o)
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uptime.o (__aeabi_idiv)
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D:/Program Files (x86)/GNU Arm Embedded Toolchain/arm-gnu-toolchain-13.3.rel1-mi
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ngw-w64-i686-arm-none-eabi/lib/gcc/arm-none-eabi/13.3.1/thumb/v6-m/nofp\libgcc.a
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(_dvmd_tls.o)
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D:/Program Files (x86)/GNU Arm Embedded Toolchain/
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arm-gnu-toolchain-13.3.rel1-mingw-w64-i686-arm-none-eabi/lib/gcc/arm-none-eabi/1
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3.3.1/thumb/v6-m/nofp\libgcc.a(_udivsi3.o) (__aeabi_idiv0)
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</pre>
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<h2>Building hello</h2>
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I can rebuild my <b>hello</b> application using the latest system
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implementation and the newly made library.
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<pre>SRCS = startup.c uplow.2.c hello.c</pre>
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Build terminates successfully, the changes in size are due to the
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difference in the system implementation.
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<pre>
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$ make
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f030f4.elf from startup.o uplow.2.o hello.o
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text data bss dec hex filename
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445 0 8 453 1c5 f030f4.elf
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f030f4.hex
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f030f4.bin
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</pre>
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Checking the map file produced in the link phase, I can see that only
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<b>puts.o</b> has been fetched from my local library.
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<pre>
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Archive member included to satisfy reference by file (symbol)
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.\libstm32.a(puts.o) hello.o (puts)
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</pre>
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<h2>Checkpoint</h2>
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I had to deal with linking with <b>gcc</b> library
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<a href="25_prototype.html">before</a>, so introducing my own library
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implementation of the standard C library output functions is a simple step.
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<p>
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<a href="28_clocks.html">Next</a>, I will continue on the topic of asynchronous serial
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transmission and look into baud rate and clock configuration.
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<hr>© 2020-2024 Renaud Fivet
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</body>
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</html>
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