runtime: add support for targets without SPI flash

artiq/firmware/runtime/config_dummy.rs

@@ -0,0 +1,19 @@
+pub fn read<F: FnOnce(Result<&[u8], ()>) -> R, R>(_key: &str, f: F) -> R {
+    f(Err(()))
+}
+
+pub fn read_str<F: FnOnce(Result<&str, ()>) -> R, R>(_key: &str, f: F) -> R {
+    f(Err(()))
+}
+
+pub fn write(_key: &str, _value: &[u8]) -> Result<(), ()> {
+    Err(())
+}
+
+pub fn remove(_key: &str) -> Result<(), ()> {
+    Err(())
+}
+
+pub fn erase() -> Result<(), ()> {
+    Err(())
+}

artiq/firmware/runtime/lib.rs

@@ -36,7 +36,10 @@ macro_rules! borrow_mut {
     })
 }
 
+#[cfg(has_spiflash)]
 mod config;
+#[cfg(not(has_spiflash))]
+#[path="config_dummy.rs"] mod config;
 mod ethmac;
 mod rtio_mgt;