diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..36d2eff
--- /dev/null
+++ b/Cargo.lock
@@ -0,0 +1,315 @@
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diff --git a/Cargo.toml b/Cargo.toml
index af04678..8a90070 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -15,6 +15,9 @@ panic-halt = "1.0.0"
 ufmt = "0.2.0"
 nb = "1.1.0"
 embedded-hal = "1.0"
+avr-device = "0.7.0"
+serde-json-core = "0.6.0"
+serde = { version = "1.0.219", default-features = false, features = ["serde_derive", "derive"] }
 
 [dependencies.arduino-hal]
 git = "https://github.com/rahix/avr-hal"
diff --git a/src/main.rs b/src/main.rs
index 0eac177..bca5f27 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -2,6 +2,7 @@
 #![no_main]
 #![feature(abi_avr_interrupt)]
 
+use core::cell::RefCell;
 use core::mem::MaybeUninit;
 
 use arduino_hal::clock::MHz16;
@@ -10,7 +11,10 @@ use arduino_hal::hal::usart::UsartReader;
 use arduino_hal::pac::USART0;
 use arduino_hal::port::mode::*;
 use arduino_hal::prelude::*;
+use avr_device::interrupt::{self, Mutex};
 use panic_halt as _;
+use serde::Deserialize;
+use serde_json_core::from_str;
 
 fn shift_out(data_pin: &mut Pin<Output, PB0>, clock_pin: &mut Pin<Output, PD4>, data: &u8) {
     for i in 0..8 {
@@ -42,11 +46,30 @@ fn update_shift_register(
 
 static mut UART_RX: MaybeUninit<UsartReader<USART0, Pin<Input, PD0>, Pin<Output, PD1>, MHz16>> = MaybeUninit::uninit();
 
-#[avr_device::interrupt(atmega328p)]
-fn USART_RX() {
-    let rx = unsafe{ &mut *UART_RX.as_mut_ptr() };
+static INPUT_LINE: Mutex<RefCell<[u8; 20]>> = Mutex::new(RefCell::new([0;20]));
 
-    rx.read();
+#[avr_device::interrupt(atmega328p)]
+unsafe fn USART_RX() {
+    let rx = &mut *UART_RX.as_mut_ptr();
+
+    static mut BUF: [u8; 20] = [0;20];
+    static mut N: usize = 0; // index into line
+
+    if let Ok(val) = rx.read() {
+        if val == b'\n' {
+
+            interrupt::free(|cs| {
+                let mut line = INPUT_LINE.borrow(cs).borrow_mut();
+                *line = BUF;
+                line[N] = b'\0';
+            });
+
+            N = 0;
+        } else {
+            BUF[N] = val;
+            N += 1;
+        }
+    }
 }
 
 
@@ -102,15 +125,50 @@ fn main() -> ! {
 
         led.toggle();
 
-        // fwd left
-        shift_register |= LEFT_FWD | RIGHT_FWD;
+        let command = decode_command();
+
+        if command.left > 0. {
+            shift_register |= LEFT_FWD;
+        }
+        if command.left < 0. {
+            shift_register |= LEFT_REV;
+        }
+
+        if command.right > 0. {
+            shift_register |= RIGHT_FWD;
+        }
+        if command.right < 0. {
+            shift_register |= RIGHT_REV;
+        }
+
+        fn to_pwm(val: f32) -> u8 {
+            (val.abs() * 255.0) as u8
+        }
 
         // 16/255
-        tc2.ocr2a.write(|w| w.bits(000)); // left
-        tc2.ocr2b.write(|w| w.bits(000)); // right
+        tc2.ocr2a.write(|w| w.bits(to_pwm(command.left))); // left
+        tc2.ocr2b.write(|w| w.bits(to_pwm(command.right))); // right
 
         update_shift_register(&mut data_pin, &mut latch_pin, &mut clock_pin, &shift_register);
 
         arduino_hal::delay_ms(1000);
     }
 }
+
+#[derive(Deserialize, Default)]
+struct Command {
+    left: f32,
+    right: f32,
+}
+
+fn decode_command() -> Command {
+    let input = interrupt::free(|cs| {
+        INPUT_LINE.borrow(cs).borrow().clone()
+    });
+
+    let Some(length) = input.iter().position(|n| *n == 0) else { return Default::default() };
+
+    let Ok(input) = str::from_utf8(&input[..length]) else { return Default::default() };
+
+    from_str(input.trim()).unwrap_or((Default::default(),0)).0
+}