diff --git a/firmware/src/board/delay.rs b/firmware/src/board/delay.rs
index e0d7305..0201681 100644
--- a/firmware/src/board/delay.rs
+++ b/firmware/src/board/delay.rs
@@ -11,9 +11,9 @@ pub struct Delay {
 }
 
 impl Delay {
-    pub fn new() -> Self {
-        let mut cp = unsafe { tm4c129x::CorePeripherals::steal() };
-        let mut syst = cp.SYST;
+    /// unsafe: must only be used once to avoid concurrent use of systick
+    pub unsafe fn new() -> Self {
+        let mut syst = CorePeripherals::steal().SYST;
         // PIOSC
         syst.set_clock_source(SystClkSource::External);
         syst.disable_interrupt();
diff --git a/firmware/src/board/softspi.rs b/firmware/src/board/softspi.rs
index f5bd286..d222634 100644
--- a/firmware/src/board/softspi.rs
+++ b/firmware/src/board/softspi.rs
@@ -137,6 +137,7 @@ impl<'d, SCK: OutputPin, MOSI: OutputPin, MISO: InputPin, D: FnMut()> SyncSoftSp
 }
 
 impl<'d, SCK: OutputPin, MOSI: OutputPin, MISO: InputPin, D: FnMut()> Transfer<u8> for SyncSoftSpi<'d, SCK, MOSI, MISO, D> {
+    // TODO: proper type
     type Error = ();
     fn transfer<'w>(&mut self, words: &'w mut [u8]) -> Result<&'w [u8], Self::Error> {
         for b in words.iter_mut() {
diff --git a/firmware/src/main.rs b/firmware/src/main.rs
index deb0bbf..d0aa4b2 100644
--- a/firmware/src/main.rs
+++ b/firmware/src/main.rs
@@ -53,6 +53,7 @@ mod ethmac;
 
 static ADC_IRQ_COUNT: Mutex<Cell<u64>> = Mutex::new(Cell::new(0));
 
+// TODO: remove
 fn get_time_ms() -> u64 {
     let adc_irq_count = cortex_m::interrupt::free(|cs| {
         ADC_IRQ_COUNT.borrow(cs).get()
@@ -115,8 +116,8 @@ fn main() -> ! {
                | |
                |_|
 "#);
-    let mut delay = board::delay::Delay::new();
-    // SCK
+    let mut delay = unsafe { board::delay::Delay::new() };
+    // CSn
     let pb4 = board::gpio::PB4.into_output();
     // SCLK
     let pb5 = board::gpio::PB5.into_output();