STM32H7: driver for LPTIM peripheral

platform/mcu/STM32H7xx/drivers/Lptim.hpp

@@ -0,0 +1,115 @@
+/***************************************************************************
+ *   Copyright (C) 2024 by Federico Amedeo Izzo IU2NUO,                    *
+ *                         Niccolò Izzo IU2KIN                             *
+ *                         Frederik Saraci IU2NRO                          *
+ *                         Silvano Seva IU2KWO                             *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 3 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ *   This program is distributed in the hope that it will be useful,       *
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
+ *   GNU General Public License for more details.                          *
+ *                                                                         *
+ *   You should have received a copy of the GNU General Public License     *
+ *   along with this program; if not, see <http://www.gnu.org/licenses/>   *
+ ***************************************************************************/
+
+#ifndef LPTIM_H
+#define LPTIM_H
+
+/**
+ * Handler class for STM32H7 LPTIM peripheral.
+ */
+class Lptim
+{
+public:
+
+    /**
+     * Constructor.
+     *
+     * @param tim: base address of timer peripheral to manage.
+     * @param baseFreq: timer base input frequency, in Hz.
+     */
+    constexpr Lptim(const uint32_t tim, const uint32_t baseFreq) : tim(tim),
+            baseFreq(baseFreq) {}
+
+    ~Lptim() = default;
+
+    /**
+     * Configure timer prescaler and auto-reload registers for a given update
+     * frequency.
+     *
+     * @param updFreq: desidered update frequency, in Hz.
+     * @return effective timer update frequency, in Hz.
+     */
+    uint32_t setUpdateFrequency(const uint32_t updFreq) const
+    {
+        /*
+         * Timer update frequency is given by:
+         * Fupd = (Fbus / prescaler) / autoreload
+         *
+         * In LPTIM the prescaler can only assume values being powers of two up
+         * to 128. To find the correct prescaler and autoreload values we start
+         * by setting the the prescaler to 1 and proceed iteratively until the
+         * autoreload value is less than the maximum allowed.
+         */
+        uint32_t div;
+        uint32_t arr;
+        uint32_t psc;
+        for(div = 0; div < 8; div += 1)
+        {
+            psc = 1 << div;
+            arr = (baseFreq / psc) / updFreq;
+            if(arr < 0xFFFF)
+                break;
+        }
+
+        // Timer needs to be enabled before configuring the other registers.
+        reinterpret_cast< LPTIM_TypeDef * >(tim)->CR   = LPTIM_CR_ENABLE;
+        reinterpret_cast< LPTIM_TypeDef * >(tim)->CFGR = div << 9;
+        reinterpret_cast< LPTIM_TypeDef * >(tim)->ARR  = arr - 1;
+
+        return (baseFreq / psc) / arr;
+    }
+
+    /**
+     * Clear and start the timer's counter.
+     */
+    inline void start() const
+    {
+        reinterpret_cast< LPTIM_TypeDef * >(tim)->CNT = 0;
+        reinterpret_cast< LPTIM_TypeDef * >(tim)->CR |= LPTIM_CR_CNTSTRT;
+    }
+
+    /**
+     * Stop the timer's counter.
+     */
+    inline void stop() const
+    {
+        // It seems that the only way to stop the LPTIM is to turn it off. Then
+        // we have to turn it on again to allow writing the configuration registers.
+        reinterpret_cast< LPTIM_TypeDef * >(tim)->CR = 0;
+        reinterpret_cast< LPTIM_TypeDef * >(tim)->CR = LPTIM_CR_ENABLE;
+    }
+
+    /**
+     * Get current value of timer's counter.
+     *
+     * @return value of timer's counter.
+     */
+    inline uint16_t value() const
+    {
+        return reinterpret_cast< LPTIM_TypeDef * >(tim)->CNT = 0;
+    }
+
+private:
+
+    const uint32_t tim;
+    const uint32_t baseFreq;
+};
+
+#endif /* LPTIM_H */