[sw/bootloader] add feature switches to makefile

sw/bootloader/makefile

@@ -18,6 +18,32 @@ USER_FLAGS += \
 -DMAKE_BOOTLOADER \
 -flto
 
+# Set which bootloader features to compile and associated settings.
+# Warning: Enabling them all while sticking to the minimal RISC-V ISA will result in a too-large binary!
+
+#USER_FLAGS += -DUART_EN=1
+#USER_FLAGS += -DUART_EN=19200
+#USER_FLAGS += -DUART_HW_HANDSHAKE_EN=0
+
+#USER_FLAGS += -DSTATUS_LED_EN=1
+#USER_FLAGS += -DSTATUS_LED_PIN=0
+
+#USER_FLAGS += -DAUTO_BOOT_TIMEOUT=10
+
+#USER_FLAGS += -DSPI_EN=0
+#USER_FLAGS += -DSPI_FLASH_CS=0
+#USER_FLAGS += -DSPI_FLASH_ADDR_BYTES=3
+#USER_FLAGS += -DSPI_FLASH_SECTOR_SIZE=65536
+#USER_FLAGS += -DSPI_FLASH_CLK_PRSC=CLK_PRSC_8
+#USER_FLAGS += -DSPI_BOOT_BASE_ADDR=0x00400000UL
+
+#USER_FLAGS += -DXIP_EN=1
+
+#USER_FLAGS += -DTWI_EN=1
+#USER_FLAGS += -DTWI_CLK_PRSC=CLK_PRSC_64
+#USER_FLAGS += -DTWI_CLK_DIV=3
+#USER_FLAGS += -DTWI_SLAVE_ID=0x50
+
 # Set path to NEORV32 root directory
 NEORV32_HOME ?= ../..