arch/arm/ameba: add shared ADC driver for RTL8721Dx / RTL8720F / RTL8721F

Documentation/platforms/arm/rtl8720f/boards/rtl8720f_evb/index.rst

@@ -41,6 +41,8 @@ Supported in this NuttX port:
   on the SDK fwlib register layer
 * PWM output exposed as a ``/dev/pwm0`` character device, driven directly on
   the SDK fwlib timer register layer
+* ADC channels exposed as an ``/dev/adc0`` character device, driven directly
+  on the SDK fwlib register layer
 
 Buttons and LEDs
 ================
@@ -144,6 +146,21 @@ example::
 
     nsh> pwm -d 25 -f 1000     # 1 kHz, 25% duty on /dev/pwm0
 
+adc
+---
+
+Minimal NSH with the ADC driver and the ``adc`` example enabled (no Wi-Fi).
+The board registers its channels from a table (see
+``boards/arm/rtl8720f/rtl8720f_evb/src/rtl8720f_adc.c``): ``/dev/adc0`` samples
+CH0 on PA13 and CH1 on PA14. Edit that table -- channel numbers and the analog
+pad each is wired to -- to match a board's wiring; the external channels
+CH0..CH5 map to pads PA13..PA18 and are muxed to the ADC function through the
+SDK ROM, while internal channels carry ``AMEBA_ADC_PIN_NC``. Every listed
+channel is sampled, in order, on each trigger. Read the channels with the
+example::
+
+    nsh> adc -n 1                        # one sweep of /dev/adc0
+
 nsh
 ---
 

Documentation/platforms/arm/rtl8721dx/boards/pke8721daf/index.rst

@@ -43,6 +43,8 @@ Supported in this NuttX port:
   on the SDK fwlib register layer
 * PWM output exposed as a ``/dev/pwm0`` character device, driven directly on
   the SDK fwlib timer register layer
+* ADC channels exposed as an ``/dev/adc0`` character device, driven directly
+  on the SDK fwlib register layer
 
 Buttons and LEDs
 ================
@@ -153,6 +155,21 @@ example::
 
     nsh> pwm -d 25 -f 1000     # 1 kHz, 25% duty on /dev/pwm0
 
+adc
+---
+
+Minimal NSH with the ADC driver and the ``adc`` example enabled (no Wi-Fi).
+The board registers its channels from a table (see
+``boards/arm/rtl8721dx/pke8721daf/src/rtl8721dx_adc.c``): ``/dev/adc0`` samples
+CH0 on PB19 and CH1 on PB18. Edit that table -- channel numbers and the analog
+pad each is wired to -- to match a board's wiring; the external channels
+CH0..CH6 map to pads PB19..PB13 and are muxed to the ADC function through the
+SDK ROM, while internal channels carry ``AMEBA_ADC_PIN_NC``. Every listed
+channel is sampled, in order, on each trigger. Read the channels with the
+example::
+
+    nsh> adc -n 1                        # one sweep of /dev/adc0
+
 Wi-Fi
 =====
 

Documentation/platforms/arm/rtl8721f/boards/rtl8721f_evb/index.rst

@@ -42,6 +42,8 @@ Supported in this NuttX port:
   on the SDK fwlib register layer
 * PWM output exposed as a ``/dev/pwm0`` character device, driven directly on
   the SDK fwlib timer register layer
+* ADC channels exposed as an ``/dev/adc0`` character device, driven directly
+  on the SDK fwlib register layer
 
 Buttons and LEDs
 ================
@@ -147,6 +149,21 @@ example::
 
     nsh> pwm -d 25 -f 1000     # 1 kHz, 25% duty on /dev/pwm0
 
+adc
+---
+
+Minimal NSH with the ADC driver and the ``adc`` example enabled (no Wi-Fi).
+The board registers its channels from a table (see
+``boards/arm/rtl8721f/rtl8721f_evb/src/rtl8721f_adc.c``): ``/dev/adc0`` samples
+CH0 on PA20 and CH1 on PA19. Edit that table -- channel numbers and the analog
+pad each is wired to -- to match a board's wiring; the external channels
+CH0..CH7 map to pads PA20,PA19,PA18,PA17,PA15,PA14,PA13,PA12 and are muxed to
+the ADC function through the SDK ROM, while internal channels carry
+``AMEBA_ADC_PIN_NC``. Every listed channel is sampled, in order, on each
+trigger. Read the channels with the example::
+
+    nsh> adc -n 1                        # one sweep of /dev/adc0
+
 nsh
 ---
 

arch/arm/src/common/ameba/Kconfig

@@ -100,4 +100,21 @@ config AMEBA_PWM
 		The driver (arch/arm/src/common/ameba/ameba_pwm.c) sits on the SDK
 		fwlib RTIM register layer and runs in polling task context.
 
+config AMEBA_ADC
+	bool "ADC"
+	default n
+	select ANALOG
+	select ADC
+	---help---
+		Expose the Ameba SAR ADC as a NuttX ADC input at /dev/adc0.  The
+		converter has one channel-switch list; the board selects which
+		channels are sampled and which analog pad each external channel is
+		wired to in its bring-up code.  Every channel is sampled, in list
+		order, on each ANIOC_TRIGGER.
+
+		The driver (arch/arm/src/common/ameba/ameba_adc.c) sits on the SDK
+		fwlib register layer and reads the auto channel-switch FIFO by
+		polling in task context (the chip does not enable a hardware
+		software-trigger path).
+
 endmenu # Ameba Peripheral Support