cpu/rpx0xx: add minimal ADC support

Signed-off-by: Dylan Laduranty <dylan.laduranty@mesotic.com>

boards/rpi-pico/Makefile.features

@@ -1,5 +1,6 @@
 CPU := rpx0xx
 
 # Put defined MCU peripherals here (in alphabetical order)
+FEATURES_PROVIDED += periph_adc
 FEATURES_PROVIDED += periph_timer
 FEATURES_PROVIDED += periph_uart

boards/rpi-pico/include/periph_conf.h

@@ -78,6 +78,21 @@ static const timer_conf_t timer_config[] = {
 
 #define TIMER_NUMOF     ARRAY_SIZE(timer_config)
 
+/**
+ * @name   ADC configuration
+ *
+ * The configuration consists simply of a list of channels that should be used
+ * @{
+ */
+static const adc_conf_t adc_config[] = {
+                                        { .pin = GPIO_PIN(0, 26), .chan = 0},
+                                        { .pin = GPIO_PIN(0, 27), .chan = 1},
+                                        { .pin = GPIO_PIN(0, 28), .chan = 2},
+                                        };
+
+#define ADC_NUMOF           ARRAY_SIZE(adc_config)
+/** @} */
+
 #ifdef __cplusplus
 }
 #endif

cpu/rpx0xx/include/periph_cpu.h

@@ -390,6 +390,14 @@ typedef struct {
 } gpio_io_ctrl_t;
 /** @} */
 
+/**
+ * @brief   ADC channel configuration data
+ */
+typedef struct {
+    gpio_t pin;             /**< Pin connected to the channel */
+    uint8_t chan;           /**< CPU ADC channel connected to the pin */
+} adc_conf_t;
+
 /**
  * @brief   Configuration details for an UART interface needed by the RPX0XX peripheral
  */

cpu/rpx0xx/periph/adc.c

@@ -0,0 +1,97 @@
+/*
+ * Copyright (C) 2023 Mesotic SAS
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     cpu_rpx0xx
+ * @ingroup     drivers_periph_adc
+ * @{
+ *
+ * @file
+ * @brief       Low-level ADC driver implementation
+ *
+ * @author      Dylan Laduranty <dylan.laduranty@mesotic.com>
+ * @}
+ */
+
+#include <errno.h>
+#include "cpu.h"
+#include "mutex.h"
+#include "periph/adc.h"
+#include "periph_conf.h"
+
+/**
+ * @brief   Lock to prevent concurrency issues when used from different threads
+ */
+static mutex_t lock;
+
+static inline void _prep(void)
+{
+    mutex_lock(&lock);
+}
+
+static inline void _done(void)
+{
+    mutex_unlock(&lock);
+}
+
+static void _disable_digital_func(gpio_t pin)
+{
+
+    const gpio_pad_ctrl_t disable_digital_pad = {
+        .input_enable = 0,
+        .output_disable = 1,
+    };
+
+    gpio_set_pad_config(pin, disable_digital_pad);
+}
+
+int adc_init(adc_t line)
+{
+    if (line >= ADC_NUMOF) {
+        return -ENODEV;
+    }
+    /* Lock mutex for exclusive access */
+    _prep();
+    /* Reset ADC peripheral */
+    periph_reset(RESETS_RESET_adc_Msk);
+    periph_reset_done(RESETS_RESET_adc_Msk);
+
+    /* Enable ADC peripheral and its clock */
+    io_reg_atomic_set(&ADC->CS, 1 << ADC_CS_EN_Pos);
+    /* Disable associated GPIO functionality as requested by datasheet */
+    _disable_digital_func(adc_config[line].pin);
+    /* Unlock mutex */
+    _done();
+    return 0;
+}
+
+int32_t adc_sample(adc_t line, adc_res_t res)
+{
+    int val = 0;
+
+    /* rpx0xx MCU only supports 12 bits resolution */
+    if (res != ADC_RES_12BIT) {
+        return -EINVAL;
+    }
+    /* Lock mutex for exclusive access */
+    _prep();
+    /* Select the channel */
+    io_reg_write_dont_corrupt(&ADC->CS, adc_config[line].chan << ADC_CS_AINSEL_Pos,
+                              ADC_CS_AINSEL_Msk);
+    /* Wait for ADC to be ready */
+    while (!(ADC->CS & ADC_CS_READY_Msk)) {}
+    /* Trigger one-shot sample */
+    io_reg_atomic_set(&ADC->CS, 1 << ADC_CS_START_ONCE_Pos);
+    /* Wait for completion */
+    while (!(ADC->CS & ADC_CS_READY_Msk)) {}
+    /* Get the result */
+    val = ADC->RESULT & ADC_RESULT_RESULT_Msk;
+    /* Unlock mutex */
+    _done();
+    return val;
+}