diff --git a/Cargo.lock b/Cargo.lock
index 36d2eff..f5302f4 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -24,6 +24,21 @@ dependencies = [
  "avr-hal-generic",
 ]
 
+[[package]]
+name = "atomic-polyfill"
+version = "1.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8cf2bce30dfe09ef0bfaef228b9d414faaf7e563035494d7fe092dba54b300f4"
+dependencies = [
+ "critical-section",
+]
+
+[[package]]
+name = "autocfg"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c08606f8c3cbf4ce6ec8e28fb0014a2c086708fe954eaa885384a6165172e7e8"
+
 [[package]]
 name = "avr-device"
 version = "0.7.0"
@@ -81,6 +96,15 @@ version = "1.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9555578bc9e57714c812a1f84e4fc5b4d21fcb063490c624de019f7464c91268"
 
+[[package]]
+name = "cobs"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0fa961b519f0b462e3a3b4a34b64d119eeaca1d59af726fe450bbba07a9fc0a1"
+dependencies = [
+ "thiserror",
+]
+
 [[package]]
 name = "critical-section"
 version = "1.2.0"
@@ -121,24 +145,37 @@ checksum = "723dce4e9f25b6e6c5f35628e144794e5b459216ed7da97b7c4b66cdb3fa82ca"
 
 [[package]]
 name = "hash32"
-version = "0.3.1"
+version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "47d60b12902ba28e2730cd37e95b8c9223af2808df9e902d4df49588d1470606"
+checksum = "b0c35f58762feb77d74ebe43bdbc3210f09be9fe6742234d573bacc26ed92b67"
 dependencies = [
  "byteorder",
 ]
 
 [[package]]
 name = "heapless"
-version = "0.8.0"
+version = "0.7.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0bfb9eb618601c89945a70e254898da93b13be0388091d42117462b265bb3fad"
+checksum = "cdc6457c0eb62c71aac4bc17216026d8410337c4126773b9c5daba343f17964f"
 dependencies = [
+ "atomic-polyfill",
  "hash32",
+ "rustc_version",
  "serde",
+ "spin",
  "stable_deref_trait",
 ]
 
+[[package]]
+name = "lock_api"
+version = "0.4.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "96936507f153605bddfcda068dd804796c84324ed2510809e5b2a624c81da765"
+dependencies = [
+ "autocfg",
+ "scopeguard",
+]
+
 [[package]]
 name = "nb"
 version = "0.1.3"
@@ -166,6 +203,17 @@ version = "1.0.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "57c0d7b74b563b49d38dae00a0c37d4d6de9b432382b2892f0574ddcae73fd0a"
 
+[[package]]
+name = "postcard"
+version = "1.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c1de96e20f51df24ca73cafcc4690e044854d803259db27a00a461cb3b9d17a"
+dependencies = [
+ "cobs",
+ "heapless",
+ "serde",
+]
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.95"
@@ -193,16 +241,31 @@ dependencies = [
  "embedded-hal 1.0.0",
  "nb 1.1.0",
  "panic-halt",
+ "postcard",
  "serde",
- "serde-json-core",
  "ufmt",
 ]
 
 [[package]]
-name = "ryu"
-version = "1.0.20"
+name = "rustc_version"
+version = "0.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "28d3b2b1366ec20994f1fd18c3c594f05c5dd4bc44d8bb0c1c632c8d6829481f"
+checksum = "cfcb3a22ef46e85b45de6ee7e79d063319ebb6594faafcf1c225ea92ab6e9b92"
+dependencies = [
+ "semver",
+]
+
+[[package]]
+name = "scopeguard"
+version = "1.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "94143f37725109f92c262ed2cf5e59bce7498c01bcc1502d7b9afe439a4e9f49"
+
+[[package]]
+name = "semver"
+version = "1.0.26"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "56e6fa9c48d24d85fb3de5ad847117517440f6beceb7798af16b4a87d616b8d0"
 
 [[package]]
 name = "serde"
@@ -213,17 +276,6 @@ dependencies = [
  "serde_derive",
 ]
 
-[[package]]
-name = "serde-json-core"
-version = "0.6.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5b81787e655bd59cecadc91f7b6b8651330b2be6c33246039a65e5cd6f4e0828"
-dependencies = [
- "heapless",
- "ryu",
- "serde",
-]
-
 [[package]]
 name = "serde_derive"
 version = "1.0.219"
@@ -235,6 +287,15 @@ dependencies = [
  "syn 2.0.104",
 ]
 
+[[package]]
+name = "spin"
+version = "0.9.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6980e8d7511241f8acf4aebddbb1ff938df5eebe98691418c4468d0b72a96a67"
+dependencies = [
+ "lock_api",
+]
+
 [[package]]
 name = "stable_deref_trait"
 version = "1.2.0"
@@ -263,6 +324,26 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "thiserror"
+version = "2.0.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "567b8a2dae586314f7be2a752ec7474332959c6460e02bde30d702a66d488708"
+dependencies = [
+ "thiserror-impl",
+]
+
+[[package]]
+name = "thiserror-impl"
+version = "2.0.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7f7cf42b4507d8ea322120659672cf1b9dbb93f8f2d4ecfd6e51350ff5b17a1d"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.104",
+]
+
 [[package]]
 name = "ufmt"
 version = "0.2.0"
diff --git a/Cargo.toml b/Cargo.toml
index 8a90070..6c2bb1c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,8 +16,8 @@ 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"] }
+postcard = "1.1.2"
 
 [dependencies.arduino-hal]
 git = "https://github.com/rahix/avr-hal"
@@ -35,4 +35,4 @@ panic = "abort"
 codegen-units = 1
 debug = true
 lto = true
-opt-level = "s"
+opt-level = "z"
diff --git a/src/main.rs b/src/main.rs
index bca5f27..509b889 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -14,7 +14,6 @@ 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 {
@@ -56,7 +55,7 @@ unsafe fn USART_RX() {
     static mut N: usize = 0; // index into line
 
     if let Ok(val) = rx.read() {
-        if val == b'\n' {
+        if val == b'\0' {
 
             interrupt::free(|cs| {
                 let mut line = INPUT_LINE.borrow(cs).borrow_mut();
@@ -68,6 +67,9 @@ unsafe fn USART_RX() {
         } else {
             BUF[N] = val;
             N += 1;
+            if N == 20 {
+                N = 0;
+            }
         }
     }
 }
@@ -162,13 +164,11 @@ struct Command {
 }
 
 fn decode_command() -> Command {
-    let input = interrupt::free(|cs| {
+    let mut 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
+    postcard::from_bytes_cobs(&mut input[..length]).unwrap_or(Default::default())
 }