https://github.com/Optiboot/optiboot/issues/131 UARTCMD was defined in

Makefile, but UART_CMD was used in Makefile.1280.  Make sure that all the
command-line options are consistantly named with the "_CMD" syntax.

optiboot/bootloaders/optiboot/Makefile

@@ -187,15 +187,15 @@ dummy = FORCE
 endif
 
 ifdef SINGLESPEED
-SSCMD = -DSINGLESPEED=1
+SS_CMD = -DSINGLESPEED=1
 endif
 
 COMMON_OPTIONS = $(BAUD_RATE_CMD) $(LED_START_FLASHES_CMD) $(BIGBOOT_CMD)
-COMMON_OPTIONS += $(SOFT_UART_CMD) $(LED_DATA_FLASH_CMD) $(LED_CMD) $(SSCMD)
+COMMON_OPTIONS += $(SOFT_UART_CMD) $(LED_DATA_FLASH_CMD) $(LED_CMD) $(SS_CMD)
 
 #UART is handled separately and only passed for devices with more than one.
 ifdef UART
-UARTCMD = -DUART=$(UART)
+UART_CMD = -DUART=$(UART)
 endif
 
 # Not supported yet

optiboot/bootloaders/optiboot/Makefile.1284

@@ -12,7 +12,7 @@ atmega644p: MCU_TARGET = atmega644p
 atmega644p: CFLAGS += $(COMMON_OPTIONS) -DBIGBOOT
 atmega644p: AVR_FREQ ?= 16000000L
 atmega644p: LDSECTIONS  = -Wl,--section-start=.text=0xfc00 -Wl,--section-start=.version=0xfffe
-atmega644p: CFLAGS += $(UARTCMD)
+atmega644p: CFLAGS += $(UART_CMD)
 atmega644p: $(PROGRAM)_atmega644p.hex
 atmega644p: $(PROGRAM)_atmega644p.lst
 
@@ -21,7 +21,7 @@ atmega1284: MCU_TARGET = atmega1284p
 atmega1284: CFLAGS += $(COMMON_OPTIONS) -DBIGBOOT
 atmega1284: AVR_FREQ ?= 16000000L
 atmega1284: LDSECTIONS  = -Wl,--section-start=.text=0x1fc00 -Wl,--section-start=.version=0x1fffe
-atmega1284: CFLAGS += $(UARTCMD)
+atmega1284: CFLAGS += $(UART_CMD)
 atmega1284: $(PROGRAM)_atmega1284p.hex
 atmega1284: $(PROGRAM)_atmega1284p.lst