diff --git a/py/emitbc.c b/py/emitbc.c
index ebc2ba500..365ec458a 100644
--- a/py/emitbc.c
+++ b/py/emitbc.c
@@ -50,7 +50,6 @@
 struct _emit_t {
     pass_kind_t pass : 8;
     uint last_emit_was_return_value : 8;
-    byte dummy_data[DUMMY_DATA_SIZE];
 
     int stack_size;
 
@@ -67,6 +66,8 @@ struct _emit_t {
     uint bytecode_offset;
     uint bytecode_size;
     byte *code_base; // stores both byte code and code info
+    // Accessed as uint, so must be aligned as such
+    byte dummy_data[DUMMY_DATA_SIZE];
 };
 
 STATIC void emit_bc_rot_two(emit_t *emit);
@@ -207,6 +208,8 @@ STATIC void emit_write_bytecode_byte_ptr(emit_t* emit, byte b, void *ptr) {
     emit_write_bytecode_byte(emit, b);
     emit_align_bytecode_to_machine_word(emit);
     mp_uint_t *c = (mp_uint_t*)emit_get_cur_to_write_bytecode(emit, sizeof(mp_uint_t));
+    // Verify thar c is already uint-aligned
+    assert(c == MP_ALIGN(c, sizeof(mp_uint_t)));
     *c = (mp_uint_t)ptr;
 }
 
diff --git a/py/misc.h b/py/misc.h
index c8ccdaa02..94a3ffaaf 100644
--- a/py/misc.h
+++ b/py/misc.h
@@ -84,6 +84,9 @@ int m_get_peak_bytes_allocated(void);
 // get the number of elements in a fixed-size array
 #define MP_ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0]))
 
+// align ptr to the nearest multiple of "alignment"
+#define MP_ALIGN(ptr, alignment) (void*)(((mp_uint_t)(ptr) + ((alignment) - 1)) & ~((alignment) - 1))
+
 /** unichar / UTF-8 *********************************************/
 
 typedef int unichar; // TODO
diff --git a/py/stream.c b/py/stream.c
index 98f62518a..2b4410728 100644
--- a/py/stream.c
+++ b/py/stream.c
@@ -98,18 +98,15 @@ STATIC mp_obj_t stream_read(uint n_args, const mp_obj_t *args) {
     }
 }
 
-STATIC mp_obj_t stream_write(mp_obj_t self_in, mp_obj_t arg) {
+mp_obj_t mp_stream_write(mp_obj_t self_in, const void *buf, mp_uint_t len) {
     struct _mp_obj_base_t *o = (struct _mp_obj_base_t *)self_in;
     if (o->type->stream_p == NULL || o->type->stream_p->write == NULL) {
         // CPython: io.UnsupportedOperation, OSError subclass
         nlr_raise(mp_obj_new_exception_msg(&mp_type_OSError, "Operation not supported"));
     }
 
-    mp_buffer_info_t bufinfo;
-    mp_get_buffer_raise(arg, &bufinfo, MP_BUFFER_READ);
-
     int error;
-    mp_int_t out_sz = o->type->stream_p->write(self_in, bufinfo.buf, bufinfo.len, &error);
+    mp_int_t out_sz = o->type->stream_p->write(self_in, buf, len, &error);
     if (out_sz == -1) {
         if (is_nonblocking_error(error)) {
             // http://docs.python.org/3/library/io.html#io.RawIOBase.write
@@ -125,6 +122,12 @@ STATIC mp_obj_t stream_write(mp_obj_t self_in, mp_obj_t arg) {
     }
 }
 
+STATIC mp_obj_t stream_write_method(mp_obj_t self_in, mp_obj_t arg) {
+    mp_buffer_info_t bufinfo;
+    mp_get_buffer_raise(arg, &bufinfo, MP_BUFFER_READ);
+    return mp_stream_write(self_in, bufinfo.buf, bufinfo.len);
+}
+
 STATIC mp_obj_t stream_readall(mp_obj_t self_in) {
     struct _mp_obj_base_t *o = (struct _mp_obj_base_t *)self_in;
     if (o->type->stream_p == NULL || o->type->stream_p->read == NULL) {
@@ -248,4 +251,4 @@ mp_obj_t mp_stream_unbuffered_iter(mp_obj_t self) {
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_read_obj, 1, 2, stream_read);
 MP_DEFINE_CONST_FUN_OBJ_1(mp_stream_readall_obj, stream_readall);
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_unbuffered_readline_obj, 1, 2, stream_unbuffered_readline);
-MP_DEFINE_CONST_FUN_OBJ_2(mp_stream_write_obj, stream_write);
+MP_DEFINE_CONST_FUN_OBJ_2(mp_stream_write_obj, stream_write_method);
diff --git a/py/stream.h b/py/stream.h
index e52508daa..4cdc1b4dc 100644
--- a/py/stream.h
+++ b/py/stream.h
@@ -32,3 +32,5 @@ MP_DECLARE_CONST_FUN_OBJ(mp_stream_write_obj);
 
 // Iterator which uses mp_stream_unbuffered_readline_obj
 mp_obj_t mp_stream_unbuffered_iter(mp_obj_t self);
+
+mp_obj_t mp_stream_write(mp_obj_t self_in, const void *buf, mp_uint_t len);
diff --git a/tests/run-tests b/tests/run-tests
index c6bc4020d..71a94f946 100755
--- a/tests/run-tests
+++ b/tests/run-tests
@@ -20,7 +20,7 @@ def rm_f(fname):
     if os.path.exists(fname):
         os.remove(fname)
 
-def run_tests(pyb, tests):
+def run_tests(pyb, tests, args):
     test_count = 0
     testcase_count = 0
     passed_count = 0
@@ -54,9 +54,15 @@ def run_tests(pyb, tests):
             # run CPython to work out expected output
             try:
                 output_expected = subprocess.check_output([CPYTHON3, '-B', test_file])
+                if args.write_exp:
+                    with open(test_file_expected, 'wb') as f:
+                        f.write(output_expected)
             except subprocess.CalledProcessError:
                 output_expected = b'CPYTHON3 CRASH'
 
+        if args.write_exp:
+            continue
+
         # run Micro Python
         if pyb is None:
             # run on PC
@@ -113,6 +119,7 @@ def main():
     cmd_parser = argparse.ArgumentParser(description='Run tests for Micro Python.')
     cmd_parser.add_argument('--pyboard', action='store_true', help='run the tests on the pyboard')
     cmd_parser.add_argument('-d', '--test-dirs', nargs='*', help='input test directories (if no files given)')
+    cmd_parser.add_argument('--write-exp', action='store_true', help='save .exp files to run tests w/o CPython')
     cmd_parser.add_argument('files', nargs='*', help='input test files')
     args = cmd_parser.parse_args()
 
@@ -139,7 +146,7 @@ def main():
         # tests explicitly given
         tests = args.files
 
-    if not run_tests(pyb, tests):
+    if not run_tests(pyb, tests, args):
         sys.exit(1)
 
 if __name__ == "__main__":
diff --git a/tests/run-tests-exp.sh b/tests/run-tests-exp.sh
new file mode 100755
index 000000000..032c42dd3
--- /dev/null
+++ b/tests/run-tests-exp.sh
@@ -0,0 +1,57 @@
+#!/bin/sh
+#
+# This is plain shell variant of run-tests script, which uses .exp files
+# as generated by run-tests --write-exp. It is useful to run testsuite
+# on embedded systems which doesn't have CPython3.
+#
+
+RM="rm -f"
+MP_PY=micropython
+
+numtests=0
+numtestcases=0
+numpassed=0
+numfailed=0
+namefailed=
+
+if [ $# -eq 0 ]
+then
+    tests="basics/*.py micropython/*.py float/*.py import/*.py io/*.py misc/*.py"
+else
+    tests="$@"
+fi
+
+for infile in $tests
+do
+    basename=`basename $infile .py`
+    outfile=${basename}.out
+    expfile=$infile.exp
+
+    $MP_PY $infile > $outfile
+    numtestcases=$(expr $numtestcases + $(cat $expfile | wc -l))
+
+    diff --brief $expfile $outfile > /dev/null
+
+    if [ $? -eq 0 ]
+    then
+        echo "pass  $infile"
+        $RM $outfile
+        numpassed=$(expr $numpassed + 1)
+    else
+        echo "FAIL  $infile"
+        numfailed=$(expr $numfailed + 1)
+        namefailed="$namefailed $basename"
+    fi
+
+    numtests=$(expr $numtests + 1)
+done
+
+echo "$numtests tests performed ($numtestcases individual testcases)"
+echo "$numpassed tests passed"
+if [ $numfailed != 0 ]
+then
+    echo "$numfailed tests failed -$namefailed"
+    exit 1
+else
+    exit 0
+fi
diff --git a/unix/file.c b/unix/file.c
index 62e3253b7..056a7b6e8 100644
--- a/unix/file.c
+++ b/unix/file.c
@@ -82,6 +82,17 @@ STATIC mp_int_t fdfile_write(mp_obj_t o_in, const void *buf, mp_uint_t size, int
     return r;
 }
 
+STATIC mp_obj_t fdfile_flush(mp_obj_t self_in) {
+#ifndef _WIN32
+    mp_obj_fdfile_t *self = self_in;
+    fsync(self->fd);
+#else
+    //TODO
+#endif
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(fdfile_flush_obj, fdfile_flush);
+
 STATIC mp_obj_t fdfile_close(mp_obj_t self_in) {
     mp_obj_fdfile_t *self = self_in;
     close(self->fd);
@@ -166,6 +177,7 @@ STATIC const mp_map_elem_t rawfile_locals_dict_table[] = {
     { MP_OBJ_NEW_QSTR(MP_QSTR_readline), (mp_obj_t)&mp_stream_unbuffered_readline_obj},
     { MP_OBJ_NEW_QSTR(MP_QSTR_readlines), (mp_obj_t)&mp_stream_unbuffered_readlines_obj},
     { MP_OBJ_NEW_QSTR(MP_QSTR_write), (mp_obj_t)&mp_stream_write_obj },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_flush), (mp_obj_t)&fdfile_flush_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_close), (mp_obj_t)&fdfile_close_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR___enter__), (mp_obj_t)&mp_identity_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR___exit__), (mp_obj_t)&fdfile___exit___obj },
diff --git a/unix/mpconfigport.h b/unix/mpconfigport.h
index 73435863b..0831e3fd3 100644
--- a/unix/mpconfigport.h
+++ b/unix/mpconfigport.h
@@ -27,7 +27,9 @@
 // options to control how Micro Python is built
 
 #define MICROPY_ALLOC_PATH_MAX      (PATH_MAX)
+#ifndef MICROPY_EMIT_X64
 #define MICROPY_EMIT_X64            (1)
+#endif
 #define MICROPY_EMIT_THUMB          (0)
 #define MICROPY_EMIT_INLINE_THUMB   (0)
 #define MICROPY_ENABLE_GC           (1)
diff --git a/unix/qstrdefsport.h b/unix/qstrdefsport.h
index de0b3d8fa..05c918017 100644
--- a/unix/qstrdefsport.h
+++ b/unix/qstrdefsport.h
@@ -32,6 +32,7 @@ Q(fileno)
 Q(makefile)
 
 Q(FileIO)
+Q(flush)
 
 Q(_os)
 Q(stat)