[U-Boot] [PATCH v2] armv7m: Add SysTick timer driver

[Phil Edworthy]

The SysTick is a 24-bit down counter that is found on all ARM Cortex
M3, M4, M7 devices and is always located at a fixed address.

Signed-off-by: Phil Edworthy <phil.edworthy at renesas.com>
---
v2:
 - Variables & constant renamed.
 - Use the calibration reg to determine if we use the cpu or ref clk
 - Use the calibration reg to get the clk rate, unless specified
---
 arch/arm/cpu/armv7m/Makefile        |   2 +
 arch/arm/cpu/armv7m/systick-timer.c | 107 ++++++++++++++++++++++++++++++++++++
 2 files changed, 109 insertions(+)
 create mode 100644 arch/arm/cpu/armv7m/systick-timer.c

diff --git a/arch/arm/cpu/armv7m/Makefile b/arch/arm/cpu/armv7m/Makefile
index aff60e8..e1a6c40 100644
--- a/arch/arm/cpu/armv7m/Makefile
+++ b/arch/arm/cpu/armv7m/Makefile
@@ -7,3 +7,5 @@
 
 extra-y := start.o
 obj-y += cpu.o
+
+obj-$(CONFIG_SYS_ARCH_TIMER) += systick-timer.o
diff --git a/arch/arm/cpu/armv7m/systick-timer.c b/arch/arm/cpu/armv7m/systick-timer.c
new file mode 100644
index 0000000..62308f9
--- /dev/null
+++ b/arch/arm/cpu/armv7m/systick-timer.c
@@ -0,0 +1,107 @@
+/*
+ * ARM Cortex M3/M4/M7 SysTick timer driver
+ * (C) Copyright 2017 Renesas Electronics Europe Ltd
+ *
+ * Based on arch/arm/mach-stm32/stm32f1/timer.c
+ * (C) Copyright 2015
+ * Kamil Lulko, <kamil.lulko at gmail.com>
+ *
+ * Copyright 2015 ATS Advanced Telematics Systems GmbH
+ * Copyright 2015 Konsulko Group, Matt Porter <mporter at konsulko.com>
+ *
+ * SPDX-License-Identifier:     GPL-2.0+
+ *
+ * The SysTick timer is a 24-bit count down timer. The clock can be either the
+ * CPU clock or a reference clock. Since the timer will wrap around very quickly
+ * when using the CPU clock, and we do not handle the timer interrupts, it is
+ * expected that this driver is only ever used with a slow reference clock.
+ */
+
+#include <common.h>
+#include <asm/io.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+/* SysTick Base Address - fixed for all Cortex M3, M4 and M7 devices */
+#define SYSTICK_BASE		0xE000E010
+
+struct cm3_systick {
+	uint32_t ctrl;
+	uint32_t reload_val;
+	uint32_t current_val;
+	uint32_t calibration;
+};
+
+#define TIMER_MAX_VAL		0x00FFFFFF
+#define SYSTICK_CTRL_EN		BIT(0)
+/* Clock source: 0 = Ref clock, 1 = CPU clock */
+#define SYSTICK_CTRL_CPU_CLK	BIT(2)
+#define SYSTICK_CAL_NOREF	BIT(31)
+#define SYSTICK_CAL_SKEW	BIT(30)
+#define SYSTICK_CAL_TENMS_MASK	0x00FFFFFF
+
+/* read the 24-bit timer */
+static ulong read_timer(void)
+{
+	struct cm3_systick *systick = (struct cm3_systick *)SYSTICK_BASE;
+
+	/* The timer counts down, therefore convert to an incrementing timer */
+	return TIMER_MAX_VAL - readl(&systick->current_val);
+}
+
+int timer_init(void)
+{
+	struct cm3_systick *systick = (struct cm3_systick *)SYSTICK_BASE;
+	u32 cal;
+
+	writel(TIMER_MAX_VAL, &systick->reload_val);
+	/* Any write to current_val reg clears it to 0 */
+	writel(0, &systick->current_val);
+
+	cal = readl(&systick->calibration);
+	if (cal & SYSTICK_CAL_NOREF)
+		/* Use CPU clock, no interrupts */
+		writel(SYSTICK_CTRL_EN | SYSTICK_CTRL_CPU_CLK, &systick->ctrl);
+	else
+		/* Use external clock, no interrupts */
+		writel(SYSTICK_CTRL_EN, &systick->ctrl);
+
+#if defined(CONFIG_SYS_HZ_CLOCK)
+	gd->arch.timer_rate_hz = CONFIG_SYS_HZ_CLOCK;
+#else
+	gd->arch.timer_rate_hz = (cal & SYSTICK_CAL_TENMS_MASK) * 100;
+#endif
+
+	gd->arch.tbl = 0;
+	gd->arch.tbu = 0;
+	gd->arch.lastinc = read_timer();
+
+	return 0;
+}
+
+/* return milli-seconds timer value */
+ulong get_timer(ulong base)
+{
+	unsigned long long t = get_ticks() * 1000;
+
+	return (ulong)((t / gd->arch.timer_rate_hz)) - base;
+}
+
+unsigned long long get_ticks(void)
+{
+	u32 now = read_timer();
+
+	if (now >= gd->arch.lastinc)
+		gd->arch.tbl += (now - gd->arch.lastinc);
+	else
+		gd->arch.tbl += (TIMER_MAX_VAL - gd->arch.lastinc) + now;
+
+	gd->arch.lastinc = now;
+
+	return gd->arch.tbl;
+}
+
+ulong get_tbclk(void)
+{
+	return gd->arch.timer_rate_hz;
+}
-- 
2.7.4