[U-Boot] [PATCH] armv7m: Add SysTick timer driver
Vikas MANOCHA
vikas.manocha at st.com
Sun Feb 12 21:09:49 UTC 2017
Hi Phil,
> -----Original Message-----
> From: Phil Edworthy [mailto:phil.edworthy at renesas.com]
> Sent: Tuesday, February 07, 2017 6:34 AM
> To: Tom Rini <trini at konsulko.com>
> Cc: Kamil Lulko <kamil.lulko at gmail.com>; Vikas MANOCHA <vikas.manocha at st.com>; Michael Kurz <michi.kurz at gmail.com>;
> Albert Aribaud <albert.u.boot at aribaud.net>; U-Boot Mailing List <u-boot at lists.denx.de>
> Subject: RE: [U-Boot] [PATCH] armv7m: Add SysTick timer driver
>
> 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.
Hmm, I wish it had some way to increase overflow time...it doesn't have the pre-scalar to divide the clock..
As this timer is same for all cortex-Mx, It makes sense to use this timer for stm32 and other cortexMx.
I didn't check calibration register : could it be useful here ?
Cheers,
Vikas
>
> Thanks
> Phil
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