1 files changed, 52 insertions, 0 deletions
diff --git a/crates/stdio-semihosting/src/lib.rs b/crates/stdio-semihosting/src/lib.rs
new file mode 100644
index 0000000..1a18b84
--- /dev/null
+++ b/crates/stdio-semihosting/src/lib.rs
@@ -0,0 +1,52 @@
+//! ThreadX stdio implemented over semihosting
+
+#![no_std]
+
+#[unsafe(no_mangle)]
+fn __rust_threadx_stdout_write(buf: &[u8]) -> usize {
+    use cortex_m_semihosting::hio;
+    // `write_all` loops until the whole buffer is sent or the host reports an
+    // error, so a success means every byte was written.
+    let Ok(mut out) = hio::hstdout() else {
+        return 0;
+    };
+    match out.write_all(buf) {
+        Ok(()) => buf.len(),
+        Err(()) => 0,
+    }
+}
+
+#[unsafe(no_mangle)]
+fn __rust_threadx_stderr_write(buf: &[u8]) -> usize {
+    use cortex_m_semihosting::hio;
+    let Ok(mut out) = hio::hstderr() else {
+        return 0;
+    };
+    match out.write_all(buf) {
+        Ok(()) => buf.len(),
+        Err(()) => 0,
+    }
+}
+
+#[unsafe(no_mangle)]
+fn __rust_threadx_stdin_read(buf: &mut [u8]) -> usize {
+    use cortex_m_semihosting::{nr, syscall};
+
+    if buf.is_empty() {
+        return 0;
+    }
+
+    // `hio` only opens the host console for writing, so open it for reading
+    // directly. `:tt` is the special semihosting path for the console.
+    let name = b":tt\0";
+    let fd = match unsafe { syscall!(OPEN, name.as_ptr(), nr::open::R, name.len() - 1) } as isize {
+        -1 => return 0,
+        fd => fd as usize,
+    };
+
+    // SYS_READ returns the number of bytes that were *not* read; on error it
+    // returns a value larger than the request, which `saturating_sub` maps to 0.
+    let not_read = unsafe { syscall!(READ, fd, buf.as_mut_ptr(), buf.len()) };
+    let _ = unsafe { syscall!(CLOSE, fd) };
+    buf.len().saturating_sub(not_read)
+}