firmware: eliminate non-io uses of std_artiq from runtime.

Just replace these with references to alloc.

artiq/firmware/runtime/cache.rs

@@ -1,6 +1,4 @@
-use std::vec::Vec;
-use std::string::String;
-use std::btree_map::BTreeMap;
+use alloc::{Vec, String, BTreeMap};
 
 #[derive(Debug)]
 struct Entry {

artiq/firmware/runtime/moninj.rs

@@ -1,6 +1,6 @@
-use std::io::{self, Read};
-use std::btree_map::BTreeMap;
+use alloc::btree_map::BTreeMap;
 
+use std::io::{self, Read};
 use sched::Io;
 use sched::{TcpListener, TcpStream};
 use board_misoc::{clock, csr};

artiq/firmware/runtime/rtio_dma.rs

@@ -1,7 +1,6 @@
-use std::mem;
-use std::vec::Vec;
-use std::string::String;
-use std::btree_map::BTreeMap;
+use core::mem;
+use alloc::{Vec, String, BTreeMap};
+
 use std::io::Write;
 
 const ALIGNMENT: usize = 64;

artiq/firmware/runtime/sched.rs

@@ -3,14 +3,14 @@
 use core::mem;
 use core::result;
 use core::cell::{Cell, RefCell};
+use alloc::Vec;
 use fringe::OwnedStack;
 use fringe::generator::{Generator, Yielder, State as GeneratorState};
 use smoltcp::wire::IpEndpoint;
 use smoltcp::socket::{SocketHandle, SocketRef};
 
-use std::vec::Vec;
-use std::io::{Read, Write, Result, Error, ErrorKind};
 use board_misoc::clock;
+use std::io::{Read, Write, Result, Error, ErrorKind};
 use urc::Urc;
 
 type SocketSet = ::smoltcp::socket::SocketSet<'static, 'static, 'static>;

artiq/firmware/runtime/session.rs

@@ -1,11 +1,9 @@
-use std::prelude::v1::*;
-use std::{mem, str};
-use std::cell::{Cell, RefCell};
-use std::io::{self, Read, Write};
-use std::error::Error;
+use core::{mem, str, cell::{Cell, RefCell}, fmt::Write as FmtWrite};
+use alloc::{Vec, String};
 use byteorder::{ByteOrder, NetworkEndian};
 
 use board_misoc::{ident, cache, config};
+use std::io::{self, Read, Write};
 use {mailbox, rpc_queue, kernel};
 use urc::Urc;
 use sched::{ThreadHandle, Io};
@@ -289,7 +287,9 @@ fn process_host_message(io: &Io,
             match unsafe { kern_load(io, session, &kernel) } {
                 Ok(()) => host_write(stream, host::Reply::LoadCompleted),
                 Err(error) => {
-                    host_write(stream, host::Reply::LoadFailed(error.description()))?;
+                    let mut description = String::new();
+                    write!(&mut description, "{}", error).unwrap();
+                    host_write(stream, host::Reply::LoadFailed(&description))?;
                     kern_acknowledge()
                 }
             },

artiq/firmware/runtime/urc.rs

@@ -1,6 +1,6 @@
-use std::rc::Rc;
-use std::ops::Deref;
-use std::fmt;
+use core::ops::Deref;
+use core::fmt;
+use alloc::rc::Rc;
 
 pub struct Urc<T: ?Sized>(Rc<T>);