diff --git a/artiq/runtime.rs/libksupport/i2c.rs b/artiq/runtime.rs/libksupport/i2c.rs
index 8a9f6da2d..0f299e6cf 100644
--- a/artiq/runtime.rs/libksupport/i2c.rs
+++ b/artiq/runtime.rs/libksupport/i2c.rs
@@ -75,7 +75,9 @@ mod imp {
 
 use self::imp::*;
 
-pub extern fn init(busno: u32) {
+pub extern fn init(busno: i32) {
+    let busno = busno as u32;
+
     // Set SCL as output, and high level
     scl_o(busno, true);
     scl_oe(busno, true);
@@ -92,7 +94,9 @@ pub extern fn init(busno: u32) {
     }
 }
 
-pub extern fn start(busno: u32) {
+pub extern fn start(busno: i32) {
+    let busno = busno as u32;
+
     // Set SCL high then SDA low
     scl_o(busno, true);
     half_period();
@@ -100,7 +104,9 @@ pub extern fn start(busno: u32) {
     half_period();
 }
 
-pub extern fn stop(busno: u32) {
+pub extern fn stop(busno: i32) {
+    let busno = busno as u32;
+
     // First, make sure SCL is low, so that the target releases the SDA line
     scl_o(busno, false);
     half_period();
@@ -112,7 +118,9 @@ pub extern fn stop(busno: u32) {
     half_period();
 }
 
-pub extern fn write(busno: u32, data: u8) -> bool {
+pub extern fn write(busno: i32, data: i8) -> bool {
+    let (busno, data) = (busno as u32, data as u8);
+
     // MSB first
     for bit in (0..8).rev() {
         // Set SCL low and set our bit on SDA
@@ -135,7 +143,9 @@ pub extern fn write(busno: u32, data: u8) -> bool {
     !sda_i(busno)
 }
 
-pub extern fn read(busno: u32, ack: bool) -> u8 {
+pub extern fn read(busno: i32, ack: bool) -> i8 {
+    let busno = busno as u32;
+
     // Set SCL low first, otherwise setting SDA as input may cause a transition
     // on SDA with SCL high which will be interpreted as START/STOP condition.
     scl_o(busno, false);
@@ -162,5 +172,5 @@ pub extern fn read(busno: u32, ack: bool) -> u8 {
     scl_o(busno, true);
     half_period();
 
-    data
+    data as i8
 }
diff --git a/artiq/runtime.rs/libksupport/lib.rs b/artiq/runtime.rs/libksupport/lib.rs
index 7c0db38c1..e8499982a 100644
--- a/artiq/runtime.rs/libksupport/lib.rs
+++ b/artiq/runtime.rs/libksupport/lib.rs
@@ -224,26 +224,26 @@ pub extern fn __artiq_terminate(exception: *const kernel_proto::Exception,
     loop {}
 }
 
-extern fn watchdog_set(ms: i64) -> usize {
+extern fn watchdog_set(ms: i64) -> i32 {
     if ms < 0 {
         artiq_raise!("ValueError", "cannot set a watchdog with a negative timeout")
     }
 
     send(&WatchdogSetRequest { ms: ms as u64 });
-    recv!(&WatchdogSetReply { id } => id)
+    recv!(&WatchdogSetReply { id } => id) as i32
 }
 
-extern fn watchdog_clear(id: usize) {
-    send(&WatchdogClear { id: id })
+extern fn watchdog_clear(id: i32) {
+    send(&WatchdogClear { id: id as usize })
 }
 
-extern fn cache_get(key: *const u8) -> (usize, *const i32) {
+extern fn cache_get(key: *const u8) -> ArtiqList<i32> {
     extern { fn strlen(s: *const c_char) -> size_t; }
     let key = unsafe { slice::from_raw_parts(key, strlen(key as *const c_char)) };
     let key = unsafe { str::from_utf8_unchecked(key) };
 
     send(&CacheGetRequest { key: key });
-    recv!(&CacheGetReply { value } => (value.len(), value.as_ptr()))
+    recv!(&CacheGetReply { value } => ArtiqList::from_slice(value))
 }
 
 extern fn cache_put(key: *const u8, list: ArtiqList<i32>) {
diff --git a/artiq/runtime.rs/libksupport/rtio.rs b/artiq/runtime.rs/libksupport/rtio.rs
index 01c400427..9bd788962 100644
--- a/artiq/runtime.rs/libksupport/rtio.rs
+++ b/artiq/runtime.rs/libksupport/rtio.rs
@@ -39,7 +39,7 @@ pub unsafe fn rtio_i_data_read(offset: usize) -> u32 {
 }
 
 #[inline(never)]
-unsafe fn process_exceptional_status(timestamp: i64, channel: u32, status: u32) {
+unsafe fn process_exceptional_status(timestamp: i64, channel: i32, status: u32) {
     if status & RTIO_O_STATUS_FULL != 0 {
         while csr::rtio::o_status_read() & RTIO_O_STATUS_FULL != 0 {}
     }
@@ -69,12 +69,12 @@ unsafe fn process_exceptional_status(timestamp: i64, channel: u32, status: u32)
     }
 }
 
-pub extern fn output(timestamp: i64, channel: u32, addr: u32, data: u32) {
+pub extern fn output(timestamp: i64, channel: i32, addr: i32, data: i32) {
     unsafe {
-        csr::rtio::chan_sel_write(channel);
+        csr::rtio::chan_sel_write(channel as u32);
         csr::rtio::o_timestamp_write(timestamp as u64);
-        csr::rtio::o_address_write(addr);
-        rtio_o_data_write(0, data);
+        csr::rtio::o_address_write(addr as u32);
+        rtio_o_data_write(0, data as u32);
         csr::rtio::o_we_write(1);
         let status = csr::rtio::o_status_read();
         if status != 0 {
@@ -83,11 +83,11 @@ pub extern fn output(timestamp: i64, channel: u32, addr: u32, data: u32) {
     }
 }
 
-pub extern fn output_wide(timestamp: i64, channel: u32, addr: u32, list: ArtiqList<i32>) {
+pub extern fn output_wide(timestamp: i64, channel: i32, addr: i32, list: ArtiqList<i32>) {
     unsafe {
-        csr::rtio::chan_sel_write(channel);
+        csr::rtio::chan_sel_write(channel as u32);
         csr::rtio::o_timestamp_write(timestamp as u64);
-        csr::rtio::o_address_write(addr);
+        csr::rtio::o_address_write(addr as u32);
         let data = list.as_slice();
         for i in 0..data.len() {
             rtio_o_data_write(i, data[i] as u32)
@@ -100,9 +100,9 @@ pub extern fn output_wide(timestamp: i64, channel: u32, addr: u32, list: ArtiqLi
     }
 }
 
-pub extern fn input_timestamp(timeout: i64, channel: u32) -> u64 {
+pub extern fn input_timestamp(timeout: i64, channel: i32) -> u64 {
     unsafe {
-        csr::rtio::chan_sel_write(channel);
+        csr::rtio::chan_sel_write(channel as u32);
         let mut status;
         loop {
             status = csr::rtio::i_status_read();
@@ -136,9 +136,9 @@ pub extern fn input_timestamp(timeout: i64, channel: u32) -> u64 {
     }
 }
 
-pub extern fn input_data(channel: u32) -> u32 {
+pub extern fn input_data(channel: i32) -> i32 {
     unsafe {
-        csr::rtio::chan_sel_write(channel);
+        csr::rtio::chan_sel_write(channel as u32);
         loop {
             let status = csr::rtio::i_status_read();
             if status == 0 { break }
@@ -153,7 +153,7 @@ pub extern fn input_data(channel: u32) -> u32 {
 
         let data = rtio_i_data_read(0);
         csr::rtio::i_re_write(1);
-        data
+        data as i32
     }
 }