firmware: allow building without system UART.

artiq/firmware/libboard/lib.rs

@@ -18,6 +18,7 @@ include!(concat!(env!("BUILDINC_DIRECTORY"), "/generated/sdram_phy.rs"));
 pub mod sdram;
 pub mod ident;
 pub mod clock;
+#[cfg(has_uart)]
 pub mod uart;
 #[cfg(has_spiflash)]
 pub mod spiflash;

artiq/firmware/libboard/uart_console.rs

@@ -1,16 +1,24 @@
 use core::fmt;
-use csr;
 
 pub struct Console;
 
 impl fmt::Write for Console {
+    #[cfg(has_uart)]
     fn write_str(&mut self, s: &str) -> Result<(), fmt::Error> {
+        use csr;
+
         for c in s.bytes() {
             unsafe {
                 while csr::uart::txfull_read() != 0 {}
                 csr::uart::rxtx_write(c)
             }
         }
+
+        Ok(())
+    }
+
+    #[cfg(not(has_uart))]
+    fn write_str(&mut self, _s: &str) -> Result<(), fmt::Error> {
         Ok(())
     }
 }

artiq/firmware/runtime/main.rs

@@ -77,6 +77,7 @@ fn startup() {
     #[cfg(has_serwb_phy_amc)]
     board_artiq::serwb::wait_init();
 
+    #[cfg(has_uart)] {
         let t = board::clock::get_ms();
         info!("press 'e' to erase startup and idle kernels...");
         while board::clock::get_ms() < t + 1000 {
@@ -88,6 +89,7 @@ fn startup() {
             }
         }
         info!("continuing boot");
+    }
 
     #[cfg(has_i2c)]
     board_artiq::i2c::init();