sandbox: Allow reading/writing of RAM buffer

It is useful to be able to save and restore the RAM contents of sandbox
U-Boot either for setting up tests, for later analysys, or for chaining
together multiple tests which need to keep the same memory contents.

Add a function to provide a memory file for U-Boot. This is read on
start-up and written when shutting down. If the file does not exist
on start-up, it will be created when shutting down.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/cpu/state.c b/arch/sandbox/cpu/state.c
index 56d5041..0380fe2 100644
--- a/arch/sandbox/cpu/state.c
+++ b/arch/sandbox/cpu/state.c
@@ -4,6 +4,7 @@
  */
 
 #include <common.h>
+#include <os.h>
 #include <asm/state.h>
 
 /* Main state record for the sandbox */
@@ -25,6 +26,10 @@
 {
 	state = &main_state;
 
+	state->ram_size = CONFIG_SYS_SDRAM_SIZE;
+	state->ram_buf = os_malloc(state->ram_size);
+	assert(state->ram_buf);
+
 	/*
 	 * Example of how to use GPIOs:
 	 *
@@ -33,3 +38,20 @@
 	 */
 	return 0;
 }
+
+int state_uninit(void)
+{
+	int err;
+
+	state = &main_state;
+
+	if (state->write_ram_buf) {
+		err = os_write_ram_buf(state->ram_buf_fname);
+		if (err) {
+			printf("Failed to write RAM buffer\n");
+			return err;
+		}
+	}
+
+	return 0;
+}