Add migration guide for developers of CCM alternative implementation
Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/docs/3.0-migration-guide.d/ccm-alt.md b/docs/3.0-migration-guide.d/ccm-alt.md
new file mode 100644
index 0000000..1abac7a
--- /dev/null
+++ b/docs/3.0-migration-guide.d/ccm-alt.md
@@ -0,0 +1,9 @@
+CCM interface changes: impact for alternative implementations
+-------------------------------------------------------------
+
+The CCM interface has changed with the addition of support for
+multi-part operations. Five new API functions have been defined:
+mbedtls_ccm_starts(), mbedtls_ccm_set_lengths(),
+mbedtls_ccm_update_ad(), mbedtls_ccm_update() and mbedtls_ccm_finish().
+Alternative implementations of CCM (`MBEDTLS_CCM_ALT`) have now to
+implement those additional five API functions.