ravedude: Make avrdude -e optional

It seems that actually some boards _don't_ want the -e option (which
instructs avrdude to do a chip erase before flashing).  For those
boards, make it possible to omit the flag.

ravedude/src/avrdude/mod.rs

@@ -7,6 +7,7 @@ pub struct AvrdudeOptions<'a> {
     pub programmer: &'a str,
     pub partno: &'a str,
     pub baudrate: Option<u32>,
+    pub do_chip_erase: bool,
 }
 
 #[derive(Debug)]
@@ -56,7 +57,11 @@ impl Avrdude {
         flash_instruction.push(bin);
         flash_instruction.push(":e");
 
-        command = command.arg("-e").arg("-D").arg("-U").arg(flash_instruction);
+        if options.do_chip_erase {
+            command = command.arg("-e");
+        }
+
+        command = command.arg("-D").arg("-U").arg(flash_instruction);
 
         let process = command.spawn().context("failed starting avrdude")?;
 

ravedude/src/board.rs

@@ -53,6 +53,7 @@ impl Board for ArduinoUno {
             programmer: "arduino",
             partno: "atmega328p",
             baudrate: None,
+            do_chip_erase: true,
         }
     }
 
@@ -82,6 +83,7 @@ impl Board for ArduinoNano {
             programmer: "arduino",
             partno: "atmega328p",
             baudrate: Some(57600),
+            do_chip_erase: true,
         }
     }
 
@@ -106,6 +108,7 @@ impl Board for ArduinoLeonardo {
             programmer: "avr109",
             partno: "atmega32u4",
             baudrate: None,
+            do_chip_erase: true,
         }
     }