diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..f1cdecb
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "nubus-to-ztex-gateware/XiBus"]
+	path = nubus-to-ztex-gateware/XiBus
+	url = git@github.com:rdolbeau/XiBus.git
diff --git a/README.md b/README.md
index d630526..d06f799 100644
--- a/README.md
+++ b/README.md
@@ -10,4 +10,4 @@ First prototype is working in a Quadra 650. It implements a single-screen-resolu
 
 Some basic acceleration now exists for 8/16/32 bits, doing rectangle screen-to-screen blits and pattern rectangle fills. 1/2/4 bits also has some acceleration, ut only for byte-aligned cases.
 
-There's also a basic RAM Disk using the 248 MiB of SDRAM not used by the framebuffer. So far this is by 32-bits accesses from the host; DMA using 1x block mode is still TBD.
\ No newline at end of file
+There's also a basic RAM Disk using the 248 MiB of SDRAM not used by the framebuffer. The driver can use either synchronous direct access to the memory bt the CPU, or asynchronous using DMA (using 16-bytes blocks). Frustratingly, the direct access methode seems faster.
\ No newline at end of file
diff --git a/nubus-to-ztex-gateware/XiBus b/nubus-to-ztex-gateware/XiBus
new file mode 160000
index 0000000..44d7267
--- /dev/null
+++ b/nubus-to-ztex-gateware/XiBus
@@ -0,0 +1 @@
+Subproject commit 44d7267ff802b54cebda7e0a643a90cff71247e4