Add missing padding to core interface

The padding is important to separate the read- and write indices by
at least one cache line, to prevent cache clean and invalidation to
corrupt data for the remote CPU.

Change-Id: I1d50ac6c63ef4cb3e11b0c293aefaac34ac8eb1f

1 files changed, 9 insertions, 0 deletions

diff --git a/kernel/ethosu_core_interface.h b/kernel/ethosu_core_interface.h
index 057e3c2..193b296 100644
--- a/kernel/ethosu_core_interface.h
+++ b/kernel/ethosu_core_interface.h
@@ -75,10 +75,19 @@ struct ethosu_core_msg {
 
 /**
  * struct ethosu_core_queue_header - Message queue header
+ *
+ * The read and write indices must be separated by at least one cache line,
+ * else updating the read index would also overwrite the write index when
+ * the cache line is flushed. Because of this the message queues should be
+ * placed on cache line aligned addresses.
+ *
+ * The cache line length for Cortex-M is typically fixed at 32 bytes. The
+ * kernel driver is setup to allocated non cached memory.
  */
 struct ethosu_core_queue_header {
 	uint32_t size;
 	uint32_t read;
+	uint32_t pad[6];
 	uint32_t write;
 };