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

[Phil Edworthy]

Hi Tom,

On 07 February 2017 14:23, Tom Rini wrote:
> On Tue, Feb 07, 2017 at 02:19:39PM +0000, Phil Edworthy wrote:
> > Hi Kamil,
> >
> > On 07 February 2017 14:12, Kamil Lulko wrote:
> > > On Mon, Feb 6, 2017 at 12:16 AM, Tom Rini <trini at konsulko.com> wrote:
> > > > On Fri, Feb 03, 2017 at 02:48:40PM +0000, Phil Edworthy wrote:
> > > >
> > > > > 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>
> > > > > ---
> > > > >  arch/arm/cpu/armv7m/Makefile        |  2 +
> > > > >  arch/arm/cpu/armv7m/systick-timer.c | 91
> > > +++++++++++++++++++++++++++++++++++++
> > > > >  2 files changed, 93 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..6ccc2fb
> > > > > --- /dev/null
> > > > > +++ b/arch/arm/cpu/armv7m/systick-timer.c
> > > > > @@ -0,0 +1,91 @@
> > > > > +/*
> > > > > + * 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+
> > > > > + */
> > > > > +
> > > > > +#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;
> > > > > +     uint32_t val;
> > > > > +     uint32_t calibration;
> > > > > +};
> > > > > +
> > > > > +#define TIMER_LOAD_VAL               0x00FFFFFF
> > > > > +#define SYSTICK_CTRL_EN              BIT(0)
> > > > > +/* Clock source: 0 = Ref clock, 1 = CPU clock */
> > > > > +#define SYSTICK_CTRL_CPU_CLK BIT(2)
> > > > > +
> > > > > +/* 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_LOAD_VAL - readl(&systick->val);
> > > > > +}
> > > > > +
> > > > > +int timer_init(void)
> > > > > +{
> > > > > +     struct cm3_systick *systick = (struct cm3_systick *)SYSTICK_BASE;
> > > > > +
> > > > > +     writel(TIMER_LOAD_VAL, &systick->reload);
> > > > > +     writel(TIMER_LOAD_VAL, &systick->val);
> > > > > +
> > > > > +#ifdef CONFIG_ARMCORTEXM3_SYSTICK_CPU
> > > > > +     /* 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);
> > > > > +#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 / CONFIG_SYS_HZ_CLOCK)) - 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_LOAD_VAL - gd->arch.lastinc) + now;
> > > > > +
> > > > > +     gd->arch.lastinc = now;
> > > > > +
> > > > > +     return gd->arch.tbl;
> > > > > +}
> > > > > +
> > > > > +ulong get_tbclk(void)
> > > > > +{
> > > > > +     return CONFIG_SYS_HZ_CLOCK;
> > > > > +}
> > > >
> > > > And (cc'ing maintainers) we could use this in place of
> > > > arch/arm/mach-stm32/*/timer.c I assume, yes?  Thanks!
> > > >
> > > > --
> > > > Tom
> > >
> > > Yes, however as far as I remember the systick is only 24-bit and
> > > usually runs on CPU clock so it will roll over too fast to be useful
> > > without using interrupts. Maybe I have missed something?
> >
> > Yes, it is only a 24-bit counter. On the device I am using, the clock
> > is not the cpu clock, but a low speed clock at 6.25MHz. Even at that
> > low clock it will still wrap every ~2.6 seconds.
> 
> So are you able to use the timer then, given the quick overflow?
Yes, I didn't see any problems. All of the udelay/mdelay calls should
work because they resolve to constantly calling get_ticks.

I guess it will not work if you attempt to time something that is
longer than 2.6 seconds though.

Thanks
Phil