Added support for USER_LIBS in the command SW makefile. (#551)

docs/datasheet/software.adoc

@@ -169,6 +169,7 @@ Make sure to add the bin folder of RISC-V GCC to your PATH variable.
 
 === Variables ===
  USER_FLAGS   - Custom toolchain flags [append only], default ""
+ USER_LIBS    - Custom libraries [append only], default ""
  EFFORT       - Optimization level, default "-Os"
  MARCH        - Machine architecture, default "rv32i_zicsr"
  MABI         - Machine binary interface, default "ilp32"
@@ -212,6 +213,8 @@ MARCH ?= rv32i_zicsr
 MABI  ?= ilp32
 # User flags for additional configuration (will be added to compiler flags)
 USER_FLAGS ?=
+# User libraries (will be included by linker)
+USER_LIBS ?=
 # Relative or absolute path to the NEORV32 home folder
 NEORV32_HOME ?= ../../..
 # *****************************************************************************
@@ -229,6 +232,7 @@ NEORV32_HOME ?= ../../..
 | `MARCH`        | The targeted RISC-V architecture/ISA
 | `MABI`         | Application binary interface (default: 32-bit integer ABI `ilp32`)
 | `USER_FLAGS`   | Additional flags that will be forwarded to the compiler tools
+| `USER_LIBS`    | Additional libraries to include during linking (`*.a`)
 | `NEORV32_HOME` | Relative or absolute path to the NEORV32 project home folder; adapt this if the makefile/project is not in the project's default `sw/example` folder
 |=======================
 

sw/common/common.mk

@@ -86,7 +86,7 @@ CORE_SRC  = $(wildcard $(NEORV32_SRC_PATH)/*.c)
 CORE_SRC += $(NEORV32_COM_PATH)/crt0.S
 
 # Linker script
-LD_SCRIPT = $(NEORV32_COM_PATH)/neorv32.ld
+LD_SCRIPT ?= $(NEORV32_COM_PATH)/neorv32.ld
 
 # Main output files
 APP_EXE  = neorv32_exe.bin
@@ -126,8 +126,10 @@ IMAGE_GEN = $(NEORV32_EXG_PATH)/image_gen
 
 # Compiler & linker flags
 CC_OPTS  = -march=$(MARCH) -mabi=$(MABI) $(EFFORT) -Wall -ffunction-sections -fdata-sections -nostartfiles -mno-fdiv
-CC_OPTS += -Wl,--gc-sections -lm -lc -lgcc -lc -g
+CC_OPTS += -g -Wl,--gc-sections
 CC_OPTS += $(USER_FLAGS)
+LD_LIBS =  -lm -lc -lgcc
+LD_LIBS += $(USER_LIBS)
 
 
 # -----------------------------------------------------------------------------
@@ -184,7 +186,7 @@ $(IMAGE_GEN): $(NEORV32_EXG_PATH)/image_gen.c
 
 # Link object files and show memory utilization
 $(APP_ELF): $(OBJ)
-	@$(CC) $(CC_OPTS) -T $(LD_SCRIPT) $(OBJ) -o $@ -lm
+	@$(CC) $(CC_OPTS) -T $(LD_SCRIPT) $(OBJ) $(LD_LIBS) -o $@
 	@echo "Memory utilization:"
 	@$(SIZE) $(APP_ELF)
 
@@ -342,6 +344,9 @@ info:
 	@echo "---------------- Info: Flags ----------------"
 	@echo "USER_FLAGS: $(USER_FLAGS)"
 	@echo "CC_OPTS:    $(CC_OPTS)"
+	@echo "---------------- Info: Libraries ----------------"
+	@echo "USER_LIBS: $(USER_LIBS)"
+	@echo "LD_LIBS:   $(LD_LIBS)"
 	@echo "---------------- Info: Host Native GCC Flags ----------------"
 	@echo "CC_X86:     $(CC_X86)"
 
@@ -374,6 +379,7 @@ help:
 	@echo ""
 	@echo "=== Variables ==="
 	@echo " USER_FLAGS   - Custom toolchain flags [append only]: \"$(USER_FLAGS)\""
+	@echo " USER_LIBS    - Custom libraries [append only]: \"$(USER_LIBS)\""
 	@echo " EFFORT       - Optimization level: \"$(EFFORT)\""
 	@echo " MARCH        - Machine architecture: \"$(MARCH)\""
 	@echo " MABI         - Machine binary interface: \"$(MABI)\""