std: xous: use constants for stdout and stderr

Use constants for the opcodes when writing to stdout or stderr.

There still is no stdin operation.

Signed-off-by: Sean Cross <sean@xobs.io>

library/std/src/os/xous/services/log.rs

@@ -45,6 +45,17 @@ impl<'a> Into<[usize; 5]> for LogScalar<'a> {
     }
 }
 
+pub(crate) enum LogLend {
+    StandardOutput = 1,
+    StandardError = 2,
+}
+
+impl Into<usize> for LogLend {
+    fn into(self) -> usize {
+        self as usize
+    }
+}
+
 /// Return a `Connection` to the log server, which is used for printing messages to
 /// the console and reporting panics. If the log server has not yet started, this
 /// will block until the server is running. It is safe to call this multiple times,

library/std/src/sys/pal/xous/stdio.rs

@@ -5,7 +5,7 @@ pub struct Stdout {}
 pub struct Stderr;
 
 use crate::os::xous::ffi::{lend, try_lend, try_scalar, Connection};
-use crate::os::xous::services::{log_server, try_connect, LogScalar};
+use crate::os::xous::services::{log_server, try_connect, LogLend, LogScalar};
 
 impl Stdin {
     pub const fn new() -> Stdin {
@@ -35,7 +35,8 @@ impl io::Write for Stdout {
             for (dest, src) in lend_buffer.0.iter_mut().zip(chunk) {
                 *dest = *src;
             }
-            lend(connection, 1, &lend_buffer.0, 0, chunk.len()).unwrap();
+            lend(connection, LogLend::StandardOutput.into(), &lend_buffer.0, 0, chunk.len())
+                .unwrap();
         }
         Ok(buf.len())
     }
@@ -61,7 +62,8 @@ impl io::Write for Stderr {
             for (dest, src) in lend_buffer.0.iter_mut().zip(chunk) {
                 *dest = *src;
             }
-            lend(connection, 1, &lend_buffer.0, 0, chunk.len()).unwrap();
+            lend(connection, LogLend::StandardError.into(), &lend_buffer.0, 0, chunk.len())
+                .unwrap();
         }
         Ok(buf.len())
     }