Add hardware_gpio accessors for Schmitt, slew rate, drive strength (fixes #290) (#464)

src/host/hardware_gpio/gpio.c

@@ -39,6 +39,31 @@ void gpio_set_oeover(uint gpio, uint value) {
 
 }
 
+void gpio_set_input_hysteresis_enabled(uint gpio, bool enabled){
+
+}
+
+bool gpio_is_input_hysteresis_enabled(uint gpio){
+    return true;
+}
+
+void gpio_set_slew_rate(uint gpio, enum gpio_slew_rate slew){
+
+}
+
+enum gpio_slew_rate gpio_get_slew_rate(uint gpio){
+    return GPIO_SLEW_RATE_FAST;
+}
+
+void gpio_set_drive_strength(uint gpio, enum gpio_drive_strength drive){
+
+}
+
+enum gpio_drive_strength gpio_get_drive_strength(uint gpio){
+    return GPIO_DRIVE_STRENGTH_4MA;
+}
+
+
 void gpio_set_irq_enabled(uint gpio, uint32_t events, bool enable) {
 
 }

src/host/hardware_gpio/include/hardware/gpio.h

@@ -27,6 +27,17 @@ enum gpio_function {
     GPIO_FUNC_NULL = 0xf,
 };
 
+enum gpio_slew_rate {
+    GPIO_SLEW_RATE_SLOW = 0,  ///< Slew rate limiting enabled
+    GPIO_SLEW_RATE_FAST = 1   ///< Slew rate limiting disabled
+};
+
+enum gpio_drive_strength {
+    GPIO_DRIVE_STRENGTH_2MA = 0, ///< 2 mA nominal drive strength
+    GPIO_DRIVE_STRENGTH_4MA = 1, ///< 4 mA nominal drive strength
+    GPIO_DRIVE_STRENGTH_8MA = 2, ///< 8 mA nominal drive strength
+    GPIO_DRIVE_STRENGTH_12MA = 3 ///< 12 mA nominal drive strength
+};
 
 #define GPIO_OUT 1
 #define GPIO_IN 0
@@ -58,6 +69,18 @@ void gpio_set_oeover(uint gpio, uint value);
 
 void gpio_set_input_enabled(uint gpio, bool enable);
 
+void gpio_set_input_hysteresis_enabled(uint gpio, bool enabled);
+
+bool gpio_is_input_hysteresis_enabled(uint gpio);
+
+void gpio_set_slew_rate(uint gpio, enum gpio_slew_rate slew);
+
+enum gpio_slew_rate gpio_get_slew_rate(uint gpio);
+
+void gpio_set_drive_strength(uint gpio, enum gpio_drive_strength drive);
+
+enum gpio_drive_strength gpio_get_drive_strength(uint gpio);
+
 // Configure a GPIO for direct input/output from software
 void gpio_init(uint gpio);
 

src/rp2_common/hardware_gpio/gpio.c

@@ -82,6 +82,53 @@ void gpio_set_oeover(uint gpio, uint value) {
     );
 }
 
+void gpio_set_input_hysteresis_enabled(uint gpio, bool enabled) {
+    invalid_params_if(GPIO, gpio >= NUM_BANK0_GPIOS);
+    if (enabled)
+        hw_set_bits(&padsbank0_hw->io[gpio], PADS_BANK0_GPIO0_SCHMITT_BITS);
+    else
+        hw_clear_bits(&padsbank0_hw->io[gpio], PADS_BANK0_GPIO0_SCHMITT_BITS);
+}
+
+
+bool gpio_is_input_hysteresis_enabled(uint gpio) {
+    invalid_params_if(GPIO, gpio >= NUM_BANK0_GPIOS);
+    return (padsbank0_hw->io[gpio] & PADS_BANK0_GPIO0_SCHMITT_BITS) != 0;
+}
+
+void gpio_set_slew_rate(uint gpio, enum gpio_slew_rate slew) {
+    invalid_params_if(GPIO, gpio >= NUM_BANK0_GPIOS);
+    hw_write_masked(&padsbank0_hw->io[gpio],
+                    (uint)slew << PADS_BANK0_GPIO0_SLEWFAST_LSB,
+                    PADS_BANK0_GPIO0_SLEWFAST_BITS
+    );
+}
+
+enum gpio_slew_rate gpio_get_slew_rate(uint gpio) {
+    invalid_params_if(GPIO, gpio >= NUM_BANK0_GPIOS);
+    return (enum gpio_slew_rate)((padsbank0_hw->io[gpio]
+            & PADS_BANK0_GPIO0_SLEWFAST_BITS)
+            >> PADS_BANK0_GPIO0_SLEWFAST_LSB);
+}
+
+
+// Enum encoding should match hardware encoding on RP2040
+static_assert(PADS_BANK0_GPIO0_DRIVE_VALUE_8MA == GPIO_DRIVE_STRENGTH_8MA, "");
+void gpio_set_drive_strength(uint gpio, enum gpio_drive_strength drive) {
+    invalid_params_if(GPIO, gpio >= NUM_BANK0_GPIOS);
+    hw_write_masked(&padsbank0_hw->io[gpio],
+                    (uint)drive << PADS_BANK0_GPIO0_DRIVE_LSB,
+                    PADS_BANK0_GPIO0_DRIVE_BITS
+    );
+}
+
+enum gpio_drive_strength gpio_get_drive_strength(uint gpio) {
+    invalid_params_if(GPIO, gpio >= NUM_BANK0_GPIOS);
+    return (enum gpio_drive_strength)((padsbank0_hw->io[gpio]
+            & PADS_BANK0_GPIO0_DRIVE_BITS)
+            >> PADS_BANK0_GPIO0_DRIVE_LSB);
+}
+
 static void gpio_irq_handler(void) {
     io_irq_ctrl_hw_t *irq_ctrl_base = get_core_num() ?
                                            &iobank0_hw->proc1_irq_ctrl : &iobank0_hw->proc0_irq_ctrl;

src/rp2_common/hardware_gpio/include/hardware/gpio.h

@@ -140,6 +140,31 @@ enum gpio_override {
     GPIO_OVERRIDE_HIGH = 3,        ///< drive high/enable output
 };
 
+/*! \brief Slew rate limiting levels for GPIO outputs
+ *  \ingroup hardware_gpio
+ *
+ * Slew rate limiting increases the minimum rise/fall time when a GPIO output
+ * is lightly loaded, which can help to reduce electromagnetic emissions.
+ * \sa gpio_set_slew_rate
+ */
+enum gpio_slew_rate {
+    GPIO_SLEW_RATE_SLOW = 0,  ///< Slew rate limiting enabled
+    GPIO_SLEW_RATE_FAST = 1   ///< Slew rate limiting disabled
+};
+
+/*! \brief Drive strength levels for GPIO outputs
+ *  \ingroup hardware_gpio
+ *
+ * Drive strength levels for GPIO outputs.
+ * \sa gpio_set_drive_strength
+ */
+enum gpio_drive_strength {
+    GPIO_DRIVE_STRENGTH_2MA = 0, ///< 2 mA nominal drive strength
+    GPIO_DRIVE_STRENGTH_4MA = 1, ///< 4 mA nominal drive strength
+    GPIO_DRIVE_STRENGTH_8MA = 2, ///< 8 mA nominal drive strength
+    GPIO_DRIVE_STRENGTH_12MA = 3 ///< 12 mA nominal drive strength
+};
+
 // ----------------------------------------------------------------------------
 // Pad Controls + IO Muxing
 // ----------------------------------------------------------------------------
@@ -246,6 +271,65 @@ void gpio_set_oeover(uint gpio, uint value);
  */
 void gpio_set_input_enabled(uint gpio, bool enabled);
 
+/*! \brief Enable/disable GPIO input hysteresis (Schmitt trigger)
+ *  \ingroup hardware_gpio
+ *
+ * Enable or disable the Schmitt trigger hysteresis on a given GPIO. This is
+ * enabled on all GPIOs by default. Disabling input hysteresis can lead to
+ * inconsistent readings when the input signal has very long rise or fall
+ * times, but slightly reduces the GPIO's input delay.
+ *
+ * \sa gpio_is_input_hysteresis_enabled
+ * \param gpio GPIO number
+ * \param enabled true to enable input hysteresis on specified GPIO
+ */
+void gpio_set_input_hysteresis_enabled(uint gpio, bool enabled);
+
+/*! \brief Determine whether input hysteresis is enabled on a specified GPIO
+ *  \ingroup hardware_gpio
+ *
+ * \sa gpio_set_input_hysteresis_enabled
+ * \param gpio GPIO number
+ */
+bool gpio_is_input_hysteresis_enabled(uint gpio);
+
+
+/*! \brief Set slew rate for a specified GPIO
+ *  \ingroup hardware_gpio
+ *
+ * \sa gpio_get_slew_rate
+ * \param gpio GPIO number
+ * \param slew GPIO output slew rate
+ */
+void gpio_set_slew_rate(uint gpio, enum gpio_slew_rate slew);
+
+/*! \brief Determine current slew rate for a specified GPIO
+ *  \ingroup hardware_gpio
+ *
+ * \sa gpio_set_slew_rate
+ * \param gpio GPIO number
+ * \return Current slew rate of that GPIO
+ */
+enum gpio_slew_rate gpio_get_slew_rate(uint gpio);
+
+/*! \brief Set drive strength for a specified GPIO
+ *  \ingroup hardware_gpio
+ *
+ * \sa gpio_get_drive_strength
+ * \param gpio GPIO number
+ * \param drive GPIO output drive strength
+ */
+void gpio_set_drive_strength(uint gpio, enum gpio_drive_strength drive);
+
+/*! \brief Determine current slew rate for a specified GPIO
+ *  \ingroup hardware_gpio
+ *
+ * \sa gpio_set_drive_strength
+ * \param gpio GPIO number
+ * \return Current drive strength of that GPIO
+ */
+enum gpio_drive_strength gpio_get_drive_strength(uint gpio);
+
 /*! \brief Enable or disable interrupts for specified GPIO
  *  \ingroup hardware_gpio
  *