From 470bee59a7508565ecc87e6011a39e15ce8363f7 Mon Sep 17 00:00:00 2001
From: Benjamin Valentin <benjamin.valentin@ml-pa.com>
Date: Wed, 18 Jan 2023 01:41:41 +0100
Subject: [PATCH] cpu/sam0_common: implement 16 bit mode by oversampling

---
 cpu/sam0_common/include/periph_cpu_common.h | 15 +++++++++--
 cpu/sam0_common/periph/adc.c                | 30 ++++++++++++++-------
 2 files changed, 34 insertions(+), 11 deletions(-)

diff --git a/cpu/sam0_common/include/periph_cpu_common.h b/cpu/sam0_common/include/periph_cpu_common.h
index 9e992b18438b..758f80497f51 100644
--- a/cpu/sam0_common/include/periph_cpu_common.h
+++ b/cpu/sam0_common/include/periph_cpu_common.h
@@ -821,9 +821,20 @@ typedef enum {
     ADC_RES_10BIT = ADC_CTRLC_RESSEL_10BIT_Val, /**< ADC resolution: 10 bit */
     ADC_RES_12BIT = ADC_CTRLC_RESSEL_12BIT_Val, /**< ADC resolution: 12 bit */
 #endif
-    ADC_RES_14BIT = 0xfe,                       /**< not supported */
-    ADC_RES_16BIT = 0xfd                        /**< not supported */
+    ADC_RES_16BIT_2SAMPL    = ( 0x1 << 2) | 0x1, /**< sum of 2 12 bit samples    */
+    ADC_RES_16BIT_4SAMPL    = ( 0x2 << 2) | 0x1, /**< sum of 4 12 bit samples    */
+    ADC_RES_16BIT_8SAMPL    = ( 0x3 << 2) | 0x1, /**< sum of 8 12 bit samples    */
+    ADC_RES_16BIT_16SAMPL   = ( 0x4 << 2) | 0x1, /**< sum of 16 12 bit samples   */
+    ADC_RES_16BIT_32SAMPL   = ( 0x5 << 2) | 0x1, /**< sum of 32 12 bit samples   */
+    ADC_RES_16BIT_64SAMPL   = ( 0x6 << 2) | 0x1, /**< sum of 64 12 bit samples   */
+    ADC_RES_16BIT_128SAMPL  = ( 0x7 << 2) | 0x1, /**< sum of 128 12 bit samples  */
+    ADC_RES_16BIT_256SAMPL  = ( 0x8 << 2) | 0x1, /**< sum of 256 12 bit samples  */
+    ADC_RES_16BIT_512SAMPL  = ( 0x9 << 2) | 0x1, /**< sum of 512 12 bit samples  */
+    ADC_RES_16BIT_1024SAMPL = ( 0xA << 2) | 0x1, /**< sum of 1024 12 bit samples */
+    ADC_RES_14BIT = 0xfe,                        /**< not supported */
 } adc_res_t;
+
+#define ADC_RES_16BIT   ADC_RES_16BIT_16SAMPL   /**< default to 16x oversampling */
 #endif /* DOXYGEN */
 
 /**
diff --git a/cpu/sam0_common/periph/adc.c b/cpu/sam0_common/periph/adc.c
index 3c906842b03c..59c236a7e811 100644
--- a/cpu/sam0_common/periph/adc.c
+++ b/cpu/sam0_common/periph/adc.c
@@ -23,6 +23,7 @@
 #include "periph/gpio.h"
 #include "periph/adc.h"
 #include "periph_conf.h"
+#include "macros/utils.h"
 #include "mutex.h"
 
 #define ENABLE_DEBUG 0
@@ -181,11 +182,7 @@ static void _setup_calibration(Adc *dev)
 
 static int _adc_configure(Adc *dev, adc_res_t res)
 {
-    /* Individual comparison necessary because ADC Resolution Bits are not
-     * numerically in order and 16Bit (averaging - not currently supported)
-     * falls between 12bit and 10bit.  See datasheet for details */
-    if (!((res == ADC_RES_8BIT) || (res == ADC_RES_10BIT) ||
-          (res == ADC_RES_12BIT))){
+    if ((res == ADC_RES_6BIT) || (res == ADC_RES_14BIT)) {
         return -1;
     }
 
@@ -203,10 +200,10 @@ static int _adc_configure(Adc *dev, adc_res_t res)
     /* Set ADC resolution */
 #ifdef ADC_CTRLC_RESSEL
     /* Reset resolution bits in CTRLC */
-    dev->CTRLC.bit.RESSEL = res;
+    dev->CTRLC.bit.RESSEL = res & 0x3;
 #else
     /* Reset resolution bits in CTRLB */
-    dev->CTRLB.bit.RESSEL = res;
+    dev->CTRLB.bit.RESSEL = res & 0x3;
 #endif
 
     /* Set Voltage Reference */
@@ -241,6 +238,12 @@ static int _adc_configure(Adc *dev, adc_res_t res)
     }
 #endif
 
+    if ((res & 0x3) == 1) {
+        dev->AVGCTRL.reg = ADC_AVGCTRL_SAMPLENUM(res >> 2);
+    } else {
+        dev->AVGCTRL.reg = 0;
+    }
+
     /*  Enable ADC Module */
     dev->CTRLA.reg |= ADC_CTRLA_ENABLE;
     _wait_syncbusy(dev);
@@ -325,14 +328,23 @@ int32_t adc_sample(adc_t line, adc_res_t res)
     /* Wait for the result */
     while (!(dev->INTFLAG.reg & ADC_INTFLAG_RESRDY)) {}
 
-    int16_t result = dev->RESULT.reg;
+    uint16_t sample = dev->RESULT.reg;
+    int result;
 
     _adc_poweroff(dev);
     _done();
 
     /* in differential mode we lose one bit for the sign */
     if (diffmode) {
-        result *= 2;
+        result = 2 * (int16_t)sample;
+    } else {
+        result = sample;
+    }
+
+    /* 16 bit mode is implemented as oversampling */
+    if ((res & 0x3) == 1) {
+        /* ADC does automatic right shifts beyond 16 samples */
+        result <<= (4 - MIN(4, res >> 2));
     }
 
     return result;