Add Makefile targets to program MCU

Also include the codgen-units=1 workaround for a rustc segfault when building
this crate in release mode. Some details here:

rust-lang/rust#62896

Cargo.toml

@@ -7,3 +7,9 @@ edition = "2018"
 [dependencies]
 # this is broken
 #ruduino = "0.2"
+
+[profile.release]
+codegen-units = 1
+lto = true
+debug = false
+opt-level = "s"

Makefile

@@ -0,0 +1,30 @@
+.PHONY: upload
+
+BIN=rust-test
+DEVICE=/dev/ttyUSB0
+RELEASE_DIR=target/avr-unknown-gnu-atmega2560/release
+ELF=$(RELEASE_DIR)/$(BIN).elf
+HEX=$(RELEASE_DIR)/$(BIN).hex
+EEP=$(RELEASE_DIR)/$(BIN).eep
+SRC=$(wildcard **/*.rs)
+
+build: $(HEX)
+
+upload: $(HEX)
+	avrdude -patmega2560 -cwiring -P$(DEVICE) -b115200 -D -Uflash:w:$(HEX):i
+
+# rust builds a .elf file
+$(ELF): $(SRC)
+	cargo build --release
+
+# convert elf to hex for the programmer, pull .eeprom out because that is
+# programmed separately
+# ihex is short for "intel hex", which is recognized by avrdude
+$(HEX): $(ELF)
+	avr-objcopy -O ihex -R .eeprom $(ELF) $(HEX)
+
+# pull .eeprom from the elf and create a separate file representing what should
+# be written to the eeprom (this file is currently unused in the build process)
+# eeprom can also be programmed by avrdude's -U
+$(EEP): $(ELF)
+	avr-objcopy -O ihex -j .eeprom --set-section-flags=.eeprom=alloc,load --no-change-warnings --change-section-lma .eeprom=0 $(ELF) $(EEP)

avr-unknown-gnu-atmega2560.json

@@ -11,7 +11,8 @@
   "late-link-args": {
       "gcc": [
           "-lgcc",
-          "-lc"
+          "-lc",
+          "-flto"
       ]
   },
   "linker": "avr-gcc",
@@ -24,7 +25,8 @@
   "pre-link-args": {
     "gcc": [
       "-mmcu=atmega2560",
-      "-Wl,--as-needed"
+      "-Wl,--as-needed",
+      "-Wl,--gc-sections"
     ]
   },
   "target-c-int-width": "16",