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[rcc] Add HSE prescaler to RTC clock source #1282

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Merged
salkinium merged 2 commits into from
Aug 16, 2025
Merged

[rcc] Add HSE prescaler to RTC clock source #1282

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302d3f3
[rcc] Add HSE prescaler to RTC clock source
salkinium Aug 15, 2025
aeee675
[board] Use HSE as RTC clock source when possible
salkinium Aug 15, 2025
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6 changes: 3 additions & 3 deletions src/modm/board/disco_f303vc/board.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,7 @@ using namespace modm::literals;
/// supplied by the on-board st-link
struct SystemClock
{
static constexpr uint32_t Hse = 8_MHz;
static constexpr uint32_t Frequency = 72_MHz;
static constexpr uint32_t Ahb = Frequency;
static constexpr uint32_t Apb1 = Frequency / 2;
Expand Down Expand Up @@ -89,13 +90,12 @@ struct SystemClock

static constexpr uint32_t Usb = Ahb / 1.5;
static constexpr uint32_t Iwdg = Rcc::LsiFrequency;
static constexpr uint32_t Rtc = Rcc::LsiFrequency;
static constexpr uint32_t Rtc = Hse / 32;

static bool inline
enable()
{
Rcc::enableLowSpeedInternalClock();
Rcc::enableRealTimeClock(Rcc::RealTimeClockSource::Lsi);
Rcc::enableRealTimeClock(Rcc::RealTimeClockSource::ExternalClock);

Rcc::enableExternalClock(); // 8MHz
const Rcc::PllFactors pllFactors{
Expand Down
8 changes: 4 additions & 4 deletions src/modm/board/disco_f401vc/board.hpp
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Expand Up @@ -36,6 +36,7 @@ using namespace modm::literals;
/// STM32F401 running at 168MHz generated from the external 8MHz crystal
struct SystemClock
{
static constexpr uint32_t Hse = 8_MHz;
static constexpr uint32_t Frequency = 84_MHz;
static constexpr uint32_t Ahb = Frequency;
static constexpr uint32_t Apb1 = Frequency / 4;
Expand Down Expand Up @@ -72,15 +73,14 @@ struct SystemClock

static constexpr uint32_t Usb = 48_MHz;
static constexpr uint32_t Iwdg = Rcc::LsiFrequency;
static constexpr uint32_t Rtc = Rcc::LsiFrequency;
static constexpr uint32_t Rtc = Hse / 25;

static bool inline
enable()
{
Rcc::enableLowSpeedInternalClock();
Rcc::enableRealTimeClock(Rcc::RealTimeClockSource::Lsi);

Rcc::enableExternalCrystal(); // 8MHz
Rcc::enableRealTimeClock(Rcc::RealTimeClockSource::ExternalClock, 25);

const Rcc::PllFactors pllFactors{
.pllM = 4, // 8MHz / M=4 -> 2MHz
.pllN = 168, // 2MHz * N=168 -> 336MHz
Expand Down
8 changes: 4 additions & 4 deletions src/modm/board/disco_f407vg/board.hpp
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Expand Up @@ -34,6 +34,7 @@ using namespace modm::literals;
/// STM32F407 running at 168MHz generated from the external 8MHz crystal
struct SystemClock
{
static constexpr uint32_t Hse = 8_MHz;
static constexpr uint32_t Frequency = 168_MHz;
static constexpr uint32_t Ahb = Frequency;
static constexpr uint32_t Apb1 = Frequency / 4;
Expand Down Expand Up @@ -83,15 +84,14 @@ struct SystemClock

static constexpr uint32_t Usb = 48_MHz;
static constexpr uint32_t Iwdg = Rcc::LsiFrequency;
static constexpr uint32_t Rtc = Rcc::LsiFrequency;
static constexpr uint32_t Rtc = Hse / 25;

static bool inline
enable()
{
Rcc::enableLowSpeedInternalClock();
Rcc::enableRealTimeClock(Rcc::RealTimeClockSource::Lsi);

Rcc::enableExternalCrystal(); // 8MHz
Rcc::enableRealTimeClock(Rcc::RealTimeClockSource::ExternalClock, 25);

const Rcc::PllFactors pllFactors{
.pllM = 4, // 8MHz / M=4 -> 2MHz
.pllN = 168, // 2MHz * N=168 -> 336MHz
Expand Down
8 changes: 4 additions & 4 deletions src/modm/board/disco_f411ve/board.hpp
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Expand Up @@ -29,6 +29,7 @@ using namespace modm::literals;
/// STM32F411 running at 96MHz generated from the external 8MHz crystal
struct SystemClock
{
static constexpr uint32_t Hse = 8_MHz;
static constexpr uint32_t Frequency = 96_MHz;
static constexpr uint32_t Ahb = Frequency;
static constexpr uint32_t Apb1 = Frequency / 2;
Expand Down Expand Up @@ -68,15 +69,14 @@ struct SystemClock

static constexpr uint32_t Usb = 48_MHz;
static constexpr uint32_t Iwdg = Rcc::LsiFrequency;
static constexpr uint32_t Rtc = Rcc::LsiFrequency;
static constexpr uint32_t Rtc = Hse / 25;

static bool inline
enable()
{
Rcc::enableLowSpeedInternalClock();
Rcc::enableRealTimeClock(Rcc::RealTimeClockSource::Lsi);

Rcc::enableExternalCrystal(); // 8MHz
Rcc::enableRealTimeClock(Rcc::RealTimeClockSource::ExternalClock, 25);

const Rcc::PllFactors pllFactors{
.pllM = 7, // 8MHz / M=7 -> ~1.14MHz
.pllN = 336, // 1.14MHz * N=336 -> 384MHz
Expand Down
8 changes: 4 additions & 4 deletions src/modm/board/disco_f429zi/board.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,7 @@ using namespace modm::literals;
/// STM32F429 running at 168MHz from the external 8MHz crystal
struct SystemClock
{
static constexpr uint32_t Hse = 8_MHz;
static constexpr uint32_t Frequency = 168_MHz;
static constexpr uint32_t Apb1 = Frequency / 4;
static constexpr uint32_t Apb2 = Frequency / 2;
Expand Down Expand Up @@ -80,15 +81,14 @@ struct SystemClock

static constexpr uint32_t Usb = 48_MHz;
static constexpr uint32_t Iwdg = Rcc::LsiFrequency;
static constexpr uint32_t Rtc = Rcc::LsiFrequency;
static constexpr uint32_t Rtc = Hse / 25;

static bool inline
enable()
{
Rcc::enableLowSpeedInternalClock();
Rcc::enableRealTimeClock(Rcc::RealTimeClockSource::Lsi);

Rcc::enableExternalCrystal(); // 8 MHz
Rcc::enableRealTimeClock(Rcc::RealTimeClockSource::ExternalClock, 25);

const Rcc::PllFactors pllFactors{
.pllM = 4, // 8MHz / M -> 2MHz
.pllN = 168, // 2MHz * N -> 336MHz
Expand Down
7 changes: 3 additions & 4 deletions src/modm/board/stm32f030f4p6_demo/board.hpp
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Expand Up @@ -31,6 +31,7 @@ using namespace modm::literals;
/// STM32F030 running at 48MHz generated from the external 8MHz crystal
struct SystemClock
{
static constexpr uint32_t Hse = 8_MHz;
static constexpr uint32_t Frequency = 48_MHz;
static constexpr uint32_t Ahb = Frequency;
static constexpr uint32_t Apb = Frequency;
Expand All @@ -52,15 +53,13 @@ struct SystemClock
static constexpr uint32_t Timer16 = Apb;
static constexpr uint32_t Timer17 = Apb;
static constexpr uint32_t Iwdg = Rcc::LsiFrequency;
static constexpr uint32_t Rtc = Rcc::LsiFrequency;
static constexpr uint32_t Rtc = Hse / 32;

static bool inline
enable()
{
Rcc::enableLowSpeedInternalClock();
Rcc::enableRealTimeClock(Rcc::RealTimeClockSource::Lsi);

Rcc::enableExternalCrystal(); // 8MHz
Rcc::enableRealTimeClock(Rcc::RealTimeClockSource::ExternalClock);

// external clock / 1 * 6 = 48MHz
const Rcc::PllFactors pllFactors{
Expand Down
4 changes: 4 additions & 0 deletions src/modm/platform/clock/stm32/module.lb
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Original file line number Diff line number Diff line change
Expand Up @@ -89,6 +89,10 @@ def build(env):
(target["family"] == "l4" and target["name"][0] in ["p", "q", "r", "s"])
properties["pllsai_p_usb"] = (target["family"] == "f7") or \
((target["family"] == "f4") and target["name"] in ["46", "69", "79"])
properties["rtcpre"] = target.family in ["f2", "f4", "f7", "h7", "l0", "l1"]
properties["cfgr_rtc"] = "CR" if target.family in ["l0", "l1"] else \
("CFGR1" if target.family in ["h5"] else "CFGR")


if target.family in ["h7"]:
if target.name in ["a3", "b0", "b3"]:
Expand Down
15 changes: 14 additions & 1 deletion src/modm/platform/clock/stm32/rcc.hpp.in
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Original file line number Diff line number Diff line change
Expand Up @@ -204,6 +204,16 @@ public:
LowSpeedExternalClock = Lse,
LowSpeedExternalCrystal = Lse
};
%% if target.family in ["l0", "l1"]
enum class
RealTimeClockHsePrescaler : uint8_t
{
Div2 = 0,
Div4 = 1,
Div8 = 2,
Div16 = 3,
};
%% endif

enum class
WatchdogClockSource : uint32_t
Expand Down Expand Up @@ -788,8 +798,11 @@ public:
enableSystemClock(SystemClockSource src, uint32_t waitCycles = 2048);

static inline bool
enableRealTimeClock(RealTimeClockSource src)
enableRealTimeClock(RealTimeClockSource src{% if rtcpre %}, {% if target.family in ["l0", "l1"] %}RealTimeClockHsePrescaler hseDiv = RealTimeClockHsePrescaler::Div16{% else %}uint8_t hseDiv = 0xff{% endif %}{% endif %})
{
%% if rtcpre
RCC->{{cfgr_rtc}} = (RCC->{{cfgr_rtc}} & ~RCC_{{cfgr_rtc}}_RTCPRE_Msk) | ((uint8_t(hseDiv) << RCC_{{cfgr_rtc}}_RTCPRE_Pos) & RCC_{{cfgr_rtc}}_RTCPRE_Msk);
%% endif
RCC->{{bdcr}} = (RCC->{{bdcr}} & ~RCC_{{bdcr}}_RTCSEL) | RCC_{{bdcr}}_RTCEN | uint32_t(src);
return true;
}
Expand Down
6 changes: 6 additions & 0 deletions src/modm/platform/rtc/stm32/rtc_impl.hpp.in
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Expand Up @@ -54,6 +54,12 @@ Rtc::initialize(bool forced)
case 320: t2ms = [](uint32_t ticks) -> uint32_t { return ((c_prediv_s - ticks) * 25u) >> 3; }; break;
// 37kHz: prediv_a=74, prediv_s=500 -> 1000/500 = 2
case 500: t2ms = [](uint32_t ticks) -> uint32_t { return (c_prediv_s - ticks) << 1; }; break;
// 250kHz: prediv_a=125, prediv_s=2000 -> 1000/2000 = 1 >> 1
case 2000: t2ms = [](uint32_t ticks) -> uint32_t { return (c_prediv_s - ticks) >> 1; }; break;
// 320kHz: prediv_a=125, prediv_s=2560 -> 1000/2560 = 25 >> 6
case 2560: t2ms = [](uint32_t ticks) -> uint32_t { return ((c_prediv_s - ticks) * 25u) >> 6; }; break;
// 1MHz: prediv_a=125, prediv_s=8000 -> 1000/8000 = 1 >> 3
case 8000: t2ms = [](uint32_t ticks) -> uint32_t { return (c_prediv_s - ticks) >> 3; }; break;
// Otherwise just do the division
default: t2ms = [](uint32_t ticks) -> uint32_t { return ((c_prediv_s - ticks) * 1000u) / (c_prediv_s + 1); }; break;
}
Expand Down
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