diff --git a/src/libc/src/lib.rs b/src/libc/src/lib.rs
index 7b53b850..2175a656 100644
--- a/src/libc/src/lib.rs
+++ b/src/libc/src/lib.rs
@@ -4,7 +4,9 @@
 
 use libboard_zynq::stdio;
 
+pub type c_char = i8;
 pub type c_int = i32;
+pub type size_t = usize;
 pub type uintptr_t = usize;
 pub type c_void = core::ffi::c_void;
 
diff --git a/src/runtime/src/analyzer.rs b/src/runtime/src/analyzer.rs
index 1c8f4f0a..3db7f9b3 100644
--- a/src/runtime/src/analyzer.rs
+++ b/src/runtime/src/analyzer.rs
@@ -71,7 +71,7 @@ async fn handle_connection(stream: &mut TcpStream) -> Result<(), Error> {
         total_byte_count: total_byte_count,
         sent_bytes: if wraparound { BUFFER_SIZE as u32 } else { total_byte_count as u32 },
         overflow_occurred: overflow_occurred,
-        log_channel: 255,
+        log_channel: pl::csr::CONFIG_RTIO_LOG_CHANNEL as u8,
         dds_onehot_sel: true  // kept for backward compatibility of analyzer dumps
     };
     debug!("{:?}", header);
diff --git a/src/runtime/src/kernel/api.rs b/src/runtime/src/kernel/api.rs
index 0153d7ab..aba60193 100644
--- a/src/runtime/src/kernel/api.rs
+++ b/src/runtime/src/kernel/api.rs
@@ -37,6 +37,7 @@ pub fn resolve(required: &[u8]) -> Option<u32> {
         api!(rtio_input_timestamp = rtio::input_timestamp),
         api!(rtio_input_data = rtio::input_data),
         api!(rtio_input_timestamped_data = rtio::input_timestamped_data),
+        api!(rtio_log = rtio::log),
 
         // Double-precision floating-point arithmetic helper functions
         // RTABI chapter 4.1.2, Table 2
diff --git a/src/runtime/src/main.rs b/src/runtime/src/main.rs
index ecd09705..40370946 100644
--- a/src/runtime/src/main.rs
+++ b/src/runtime/src/main.rs
@@ -3,6 +3,7 @@
 #![recursion_limit="1024"]  // for futures_util::select!
 #![feature(alloc_error_handler)]
 #![feature(panic_info_message)]
+#![feature(c_variadic)]
 
 extern crate alloc;
 
diff --git a/src/runtime/src/rtio.rs b/src/runtime/src/rtio.rs
index ef5b9d18..0918d669 100644
--- a/src/runtime/src/rtio.rs
+++ b/src/runtime/src/rtio.rs
@@ -1,5 +1,9 @@
-use core::ptr::{read_volatile, write_volatile};
+use core::ptr::{self, read_volatile, write_volatile};
+use core::ffi::VaList;
+use alloc::vec;
 use cslice::CSlice;
+use libc::{c_char, c_int, size_t};
+
 use crate::artiq_raise;
 
 use crate::pl::csr;
@@ -198,3 +202,34 @@ pub extern fn input_timestamped_data(timeout: i64, channel: i32) -> TimestampedD
         }
     }
 }
+
+extern "C" {
+    fn vsnprintf_(buffer: *mut c_char, count: size_t, format: *const c_char, va: VaList) -> c_int;
+}
+
+fn write_rtio_log(data: &[i8]) {
+    unsafe {
+        csr::rtio::target_write(csr::CONFIG_RTIO_LOG_CHANNEL << 8);
+
+        let mut word: u32 = 0;
+        for i in 0..data.len() {
+            word <<= 8;
+            word |= data[i] as u32;
+            if i % 4 == 3 {
+                rtio_o_data_write(0, word);
+                word = 0;
+            }
+        }
+
+        if word != 0 {
+            rtio_o_data_write(0, word);
+        }
+    }
+}
+
+pub unsafe extern fn log(fmt: *const c_char, mut args: ...) {
+    let size = vsnprintf_(ptr::null_mut(), 0, fmt, args.as_va_list()) as usize;
+    let mut buf = vec![0; size + 1];
+    vsnprintf_(buf.as_mut_ptr(), size + 1, fmt, args.as_va_list());
+    write_rtio_log(buf.as_slice());
+}