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Date: Thu, 13 Nov 2008 19:15:52 +0100
From: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
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Subject: Re: [Xenomai-help] Mode switch when using RT heap on ARM
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To: Wolfgang Grandegger <wg@domain.hid>
Cc: xenomai-help <xenomai@xenomai.org>

Wolfgang Grandegger wrote:
> Hello,
> 
> I realized that accessing memory allocated with rt_heap_alloc() causes
> mode switches on ARM i.mx31. The attached patch provides a demo program
> to demonstrate the problem, which actually does *not* show up on my
> PowerPC TQM5200 board.

Index: xenomai-2.4.x/examples/native/rtheap.c
===================================================================
--- /dev/null
+++ xenomai-2.4.x/examples/native/rtheap.c
@@ -0,0 +1,164 @@
+#include <stdio.h>
+#include <signal.h>
+#include <unistd.h>
+#include <sys/mman.h>
+
+#include <native/task.h>
+#include <native/timer.h>
+#include <native/heap.h>
+
+#define USE_HEAP
+//#define USE_SIGXCPU
+
+#define HEAP_SIZE (1024*1024)
+#define HEAP_MODE 0		/* Local heap. */
+
+RT_HEAP heap_desc;
+RT_TASK demo_task;
+
+
+static int block_sizes[] = {16, 20, 90, 150, 310, 800, 1000};
+
+/* NOTE: error handling omitted. */
+
+void demo(void *arg)
+{
+	RTIME now, previous;
+	void *block;
+	int sizes = sizeof(block_sizes) / sizeof(int);
+	int count = 0;
+	int size, err;
+	int *ptr;
+
+#ifdef USE_SIGXCPU
+	/* Ask Xenomai to warn us upon switches to secondary mode. */
+	rt_task_set_mode(0, T_WARNSW, NULL);
+#endif
+
+	/*
+	 * Arguments: &task (NULL=self),
+	 *            start time,
+	 *            period (here: 1 s)
+	 */
+	rt_task_set_periodic(NULL, TM_NOW, 10000000);
+	previous = rt_timer_read();
+
+	while (1) {
+		rt_task_wait_period(NULL);
+		now = rt_timer_read();
+
+		size = block_sizes[count % sizes];
+#ifdef USE_HEAP
+		/*
+		 * Request a 16-bytes block, asking for a non-blocking call
+		 * since only Xenomai tasks may block.
+		 */
+		err = rt_heap_alloc(&heap_desc, size, TM_NONBLOCK, &block);
+		if (err) {
+			printf("rt_heap_alloc() failed with %d\n", err);
+			break;
+		}
+
+		ptr = (int *)block;
+		*ptr = 0xdeadbeef;
+		if (*ptr != 0xdeadbeef) {
+			printf("Write/read test to heap failed\n");
+			break;
+		}
+
+		ptr = (int *)(block + size - sizeof(int));

This is not guaranteed to be aligned on an int. Could you try:

		ptr = (int *)(((unsigned long) block + size - sizeof(int)) & ~3);

-- 
                                                 Gilles.