2 files changed, 23 insertions, 1 deletions
diff --git a/py/reader.c b/py/reader.c
index 151e04cac..8feb6d752 100644
--- a/py/reader.c
+++ b/py/reader.c
@@ -50,7 +50,7 @@ static mp_uint_t mp_reader_mem_readbyte(void *data) {
 
 static void mp_reader_mem_close(void *data) {
     mp_reader_mem_t *reader = (mp_reader_mem_t *)data;
-    if (reader->free_len > 0) {
+    if (reader->free_len > 0 && reader->free_len != MP_READER_IS_ROM) {
         m_del(char, (char *)reader->beg, reader->free_len);
     }
     m_del_obj(mp_reader_mem_t, reader);
@@ -67,6 +67,19 @@ void mp_reader_new_mem(mp_reader_t *reader, const byte *buf, size_t len, size_t
     reader->close = mp_reader_mem_close;
 }
 
+const uint8_t *mp_reader_try_read_rom(mp_reader_t *reader, size_t len) {
+    if (reader->readbyte != mp_reader_mem_readbyte) {
+        return NULL;
+    }
+    mp_reader_mem_t *m = reader->data;
+    if (m->free_len != MP_READER_IS_ROM) {
+        return NULL;
+    }
+    const uint8_t *data = m->cur;
+    m->cur += len;
+    return data;
+}
+
 #if MICROPY_READER_POSIX
 
 #include <sys/stat.h>
diff --git a/py/reader.h b/py/reader.h
index 5cb1e6796..301c70ab3 100644
--- a/py/reader.h
+++ b/py/reader.h
@@ -28,6 +28,10 @@
 
 #include "py/obj.h"
 
+// Pass to the `free_len` argument to `mp_reader_new_mem` to indicate that the data is in ROM.
+// This means that the data is addressable and will remain valid at least until a soft reset.
+#define MP_READER_IS_ROM ((size_t)-1)
+
 // the readbyte function must return the next byte in the input stream
 // it must return MP_READER_EOF if end of stream
 // it can be called again after returning MP_READER_EOF, and in that case must return MP_READER_EOF
@@ -43,4 +47,9 @@ void mp_reader_new_mem(mp_reader_t *reader, const byte *buf, size_t len, size_t
 void mp_reader_new_file(mp_reader_t *reader, qstr filename);
 void mp_reader_new_file_from_fd(mp_reader_t *reader, int fd, bool close_fd);
 
+// Try to efficiently read the given number of bytes from a ROM-based reader.
+// Returns a valid, non-NULL pointer to the requseted data if the reader points to ROM.
+// Returns NULL if the reader does not point to ROM.
+const uint8_t *mp_reader_try_read_rom(mp_reader_t *reader, size_t len);
+
 #endif // MICROPY_INCLUDED_PY_READER_H