hw/watchdog/cmsdk_apb_watchdog: Implement CMSDK APB watchdog module

The Arm Cortex-M System Design Kit includes a simple watchdog module
based on a 32-bit down-counter. Implement this.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 59 insertions, 0 deletions

diff --git a/include/hw/watchdog/cmsdk-apb-watchdog.h b/include/hw/watchdog/cmsdk-apb-watchdog.h
new file mode 100644
index 0000000..ab8b598
--- /dev/null
+++ b/include/hw/watchdog/cmsdk-apb-watchdog.h
@@ -0,0 +1,59 @@
+/*
+ * ARM CMSDK APB watchdog emulation
+ *
+ * Copyright (c) 2018 Linaro Limited
+ * Written by Peter Maydell
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License version 2 or
+ *  (at your option) any later version.
+ */
+
+/*
+ * This is a model of the "APB watchdog" which is part of the Cortex-M
+ * System Design Kit (CMSDK) and documented in the Cortex-M System
+ * Design Kit Technical Reference Manual (ARM DDI0479C):
+ * https://developer.arm.com/products/system-design/system-design-kits/cortex-m-system-design-kit
+ *
+ * QEMU interface:
+ *  + QOM property "wdogclk-frq": frequency at which the watchdog is clocked
+ *  + sysbus MMIO region 0: the register bank
+ *  + sysbus IRQ 0: watchdog interrupt
+ *
+ * In real hardware the watchdog's reset output is just a GPIO line
+ * which can then be masked by the board or treated as a simple interrupt.
+ * (For instance the IoTKit does this with the non-secure watchdog, so that
+ * secure code can control whether non-secure code can perform a system
+ * reset via its watchdog.) In QEMU, we just wire up the watchdog reset
+ * to watchdog_perform_action(), at least for the moment.
+ */
+
+#ifndef CMSDK_APB_WATCHDOG_H
+#define CMSDK_APB_WATCHDOG_H
+
+#include "hw/sysbus.h"
+#include "hw/ptimer.h"
+
+#define TYPE_CMSDK_APB_WATCHDOG "cmsdk-apb-watchdog"
+#define CMSDK_APB_WATCHDOG(obj) OBJECT_CHECK(CMSDKAPBWatchdog, (obj), \
+                                              TYPE_CMSDK_APB_WATCHDOG)
+
+typedef struct CMSDKAPBWatchdog {
+    /*< private >*/
+    SysBusDevice parent_obj;
+
+    /*< public >*/
+    MemoryRegion iomem;
+    qemu_irq wdogint;
+    uint32_t wdogclk_frq;
+    struct ptimer_state *timer;
+
+    uint32_t control;
+    uint32_t intstatus;
+    uint32_t lock;
+    uint32_t itcr;
+    uint32_t itop;
+    uint32_t resetstatus;
+} CMSDKAPBWatchdog;
+
+#endif