boards/arm/stm32f4discovery: Add support to HX711 ADC

This commit adds support for the HX711 ADC in the STM32F4-Discovery
board and updates the board documentation accordingly.

Signed-off-by: Rodrigo Sim <rcsim10@gmail.com>

Documentation/platforms/arm/stm32f4/boards/stm32f4discovery/index.rst

@@ -2203,3 +2203,60 @@ NOTES:
    Host Compiler:  I use the MingW compiler which can be downloaded from
    http://www.mingw.org/.  If you are using GNUWin32, then it is recommended
    the you not install the optional MSYS components as there may be conflicts.
+
+HX711
+-----
+
+HX711 is a precision 24-bit analog-to-digital converter (ADC)
+designed for weigh scales and industrial control applications.
+It interfaces load cells via a simple two-wire serial interface
+(clock and data) and provides high-resolution digital weight
+measurements.
+
+**Enable the following options using ``make menuconfig``:**
+
+::
+
+    CONFIG_ADC=y
+    CONFIG_ANALOG=y
+    CONFIG_ADC_HX711=y
+    CONFIG_EXAMPLES_HX711=y
+
+**Wiring:**
+
+Connect the HX711 to the STM32F4 board using the following pins:
+
++--------+------+
+| HX711  | PIN  |
++========+======+
+| SCK    | PB1  |
++--------+------+
+| DT     | PB2  |
++--------+------+
+
+**NSH usage:**
+
+::
+
+    NuttShell (NSH) NuttX-12.10.0 
+    nsh> hx711 -D
+    Current settings for: /dev/hx711_0
+    average.............: 1
+    channel.............: a
+    gain................: 128
+    value per unit......: 0
+    nsh> hx711 -v 813 -t 10
+    Taring with *float*g precision
+    nsh> hx711 -r 10
+    -2
+    0
+    0
+    -1
+    -3
+    -3
+    -2
+    -2
+    -4
+    -4
+
+For more details, refer to the official `HX711 NuttX documentation <https://nuttx.apache.org/docs/latest/components/drivers/character/analog/adc/hx711/index.html>`_.

boards/arm/stm32/stm32f4discovery/src/CMakeLists.txt

@@ -171,6 +171,10 @@ if(CONFIG_LCD_ST7789)
   list(APPEND SRCS stm32_st7789.c)
 endif()
 
+if(CONFIG_ADC_HX711)
+  list(APPEND SRCS stm32_hx711.c)
+endif()
+
 target_sources(board PRIVATE ${SRCS})
 
 # TODO: make this the default and then allow boards to redefine

boards/arm/stm32/stm32f4discovery/src/Make.defs

@@ -189,6 +189,10 @@ ifeq ($(CONFIG_USBDEV_COMPOSITE),y)
   CSRCS += stm32_composite.c
 endif
 
+ifeq ($(CONFIG_ADC_HX711),y)
+CSRCS += stm32_hx711.c
+endif
+
 DEPPATH += --dep-path board
 VPATH += :board
 CFLAGS += ${INCDIR_PREFIX}$(TOPDIR)$(DELIM)arch$(DELIM)$(CONFIG_ARCH)$(DELIM)src$(DELIM)board$(DELIM)board

boards/arm/stm32/stm32f4discovery/src/stm32_bringup.c

@@ -637,5 +637,13 @@ int stm32_bringup(void)
     }
 #endif
 
+#ifdef CONFIG_ADC_HX711
+  ret = stm32_hx711_initialize();
+  if (ret != OK)
+    {
+      aerr("ERROR: Failed to initialize hx711: %d\n", ret);
+    }
+#endif
+
   return ret;
 }

boards/arm/stm32/stm32f4discovery/src/stm32_hx711.c

@@ -0,0 +1,104 @@
+/****************************************************************************
+ * boards/arm/stm32/stm32f4discovery/src/stm32_hx711.c
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+#include <nuttx/analog/hx711.h>
+#include <nuttx/compiler.h>
+#include <arch/board/board.h>
+#include <arch/stm32/chip.h>
+#include <debug.h>
+
+#include "stm32_gpio.h"
+#include "stm32f4discovery.h"
+
+/****************************************************************************
+ * Private Function Prototypes
+ ****************************************************************************/
+
+static int stm32_hx711_clock_set(unsigned char minor, int value);
+static int stm32_hx711_data_read(unsigned char minor);
+static int stm32_hx711_data_irq(unsigned char minor,
+                                xcpt_t handler, void *arg);
+
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+struct hx711_lower_s g_lower =
+{
+  .data_read = stm32_hx711_data_read,
+  .clock_set = stm32_hx711_clock_set,
+  .data_irq  = stm32_hx711_data_irq,
+  .cleanup = NULL
+};
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+static int stm32_hx711_clock_set(unsigned char minor, int value)
+{
+  UNUSED(minor);
+
+  stm32_gpiowrite(HX711_CLK_PIN, value);
+  return OK;
+}
+
+static int stm32_hx711_data_read(unsigned char minor)
+{
+  UNUSED(minor);
+
+  return stm32_gpioread(HX711_DATA_PIN);
+}
+
+static int stm32_hx711_data_irq(unsigned char minor,
+                                xcpt_t handler, void *arg)
+{
+  UNUSED(minor);
+
+  return stm32_gpiosetevent(HX711_DATA_PIN, false, true, true, handler, arg);
+};
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+int stm32_hx711_initialize(void)
+{
+  int ret;
+
+  stm32_configgpio(HX711_DATA_PIN);
+  stm32_configgpio(HX711_CLK_PIN);
+
+  ret = hx711_register(0, &g_lower);
+  if (ret != 0)
+    {
+      aerr("ERROR: Failed to register hx711 device: %d\n", ret);
+      return -1;
+    }
+
+  return OK;
+}

boards/arm/stm32/stm32f4discovery/src/stm32f4discovery.h

@@ -243,6 +243,15 @@
 
 #define GPIO_SX127X_RESET   (GPIO_OUTPUT|GPIO_PUSHPULL|GPIO_OUTPUT_CLEAR|\
                              GPIO_SPEED_50MHz|GPIO_PORTD|GPIO_PIN4)
+/* HX711 PINs */
+
+#ifdef CONFIG_ADC_HX711
+#  define HX711_CLK_PIN     (GPIO_OUTPUT|GPIO_PUSHPULL|GPIO_OUTPUT_SET|\
+                            GPIO_SPEED_2MHz|GPIO_PULLUP|\
+                            GPIO_PORTB|GPIO_PIN1)
+#  define HX711_DATA_PIN    (GPIO_INPUT|GPIO_SPEED_2MHz|GPIO_PULLUP|GPIO_EXTI|\
+                            GPIO_PORTB|GPIO_PIN2)
+#endif /* CONFIG_ADC_HX711 */
 
 /* PWM
  *
@@ -902,5 +911,17 @@ int stm32_gs2200m_initialize(const char *devpath, int bus);
 int stm32_djoy_initialize(void);
 #endif
 
+/****************************************************************************
+ * Name: stm32_hx711_initialize
+ *
+ * Description:
+ *   Initialize hx711 chip
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_ADC_HX711
+int stm32_hx711_initialize(void);
+#endif
+
 #endif /* __ASSEMBLY__ */
 #endif /* __BOARDS_ARM_STM32_STM32F4DISCOVERY_SRC_STM32F4DISCOVERY_H */