xtensa/esp/rmt: Add the lower-half implementation of the RMT driver

The lower-half implementation of the RMT character driver based on
Espressif HAL enables using the RMT peripheral of ESP32, ESP32-S2
and ESP32-S3 as a common xtensa-based Espressif driver.

The RMT packages on Espressif SoCs are 4-byte long and are known as
"items". Please check the Techinal Reference Manual of the chip to
obtain more details.

Kconfig

@@ -1729,7 +1729,7 @@ endif # DEBUG_REGMAP
 config DEBUG_RMT
 	bool "RMT Debug Features"
 	default n
-	depends on ESP32_RMT
+	depends on RMT
 	---help---
 		Enable RMT debug features.
 

arch/xtensa/src/Makefile

@@ -129,6 +129,7 @@ endif
 
 VPATH += chip
 VPATH += common
+VPATH += common/espressif
 VPATH += $(ARCH_SUBDIR)
 VPATH += $(CHIP_DIR)
 

arch/xtensa/src/common/espressif/Kconfig

@@ -0,0 +1,7 @@
+config ESP_RMT
+	bool "Remote Control Module (RMT)"
+	default n
+	depends on RMT
+	---help---
+		Remote Control Module is currently used to control WS2812
+		RGB LED normally used on LED strips.

arch/xtensa/src/common/espressif/Make.defs

@@ -0,0 +1,26 @@
+############################################################################
+# arch/xtensa/src/common/espressif/Make.defs
+#
+# 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.
+#
+############################################################################
+
+ifeq ($(CONFIG_ESP_RMT),y)
+CHIP_CSRCS += esp_rmt.c
+ifeq ($(CONFIG_WS2812_NON_SPI_DRIVER),y)
+CHIP_CSRCS += esp_ws2812.c
+endif
+endif

arch/xtensa/src/common/espressif/esp_rmt.h

@@ -0,0 +1,109 @@
+/****************************************************************************
+ * arch/xtensa/src/common/espressif/esp_rmt.h
+ *
+ * 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.
+ *
+ ****************************************************************************/
+
+#ifndef __ARCH_XTENSA_SRC_COMMON_ESPRESSIF_ESP_RMT_H
+#define __ARCH_XTENSA_SRC_COMMON_ESPRESSIF_ESP_RMT_H
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+#include <semaphore.h>
+#include <nuttx/spinlock.h>
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+#define RMT_MEM_ITEM_NUM SOC_RMT_MEM_WORDS_PER_CHANNEL
+
+#define RMT_DEFAULT_CLK_DIV 1
+
+/* Channel can work during APB clock scaling */
+
+#define RMT_CHANNEL_FLAGS_AWARE_DFS (1 << 0)
+
+/* Invert RMT signal */
+
+#define RMT_CHANNEL_FLAGS_INVERT_SIG (1 << 1)
+
+/****************************************************************************
+ * Public Types
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Data
+ ****************************************************************************/
+
+#ifndef __ASSEMBLY__
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+/****************************************************************************
+ * Public Functions Prototypes
+ ****************************************************************************/
+
+#if defined(CONFIG_ESP_RMT)
+
+/****************************************************************************
+ * Name: esp_rmt_tx_init
+ *
+ * Description:
+ *   Initialize the selected RMT device in TX mode
+ *
+ * Input Parameters:
+ *   ch   - the RMT's channel that will be used
+ *   pin  - The pin used for the TX channel
+ *
+ * Returned Value:
+ *   Valid RMT device structure reference on success; NULL, otherwise.
+ *
+ ****************************************************************************/
+
+struct rmt_dev_s *esp_rmt_tx_init(int ch, int pin);
+
+/****************************************************************************
+ * Name: esp_rmt_rx_init
+ *
+ * Description:
+ *   Initialize the selected RMT device in RC mode
+ *
+ * Input Parameters:
+ *   ch   - the RMT's channel that will be used
+ *   pin  - The pin used for the RX channel
+ *
+ * Returned Value:
+ *   Valid RMT device structure reference on success; NULL, otherwise.
+ *
+ ****************************************************************************/
+
+struct rmt_dev_s *esp_rmt_rx_init(int ch, int pin);
+
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* __ASSEMBLY__ */
+
+#endif /* __ARCH_XTENSA_SRC_COMMON_ESPRESSIF_ESP_RMT_H */

drivers/rmt/Kconfig

@@ -33,4 +33,15 @@ config RMT_DEFAULT_RX_BUFFER_SIZE
 		The RMT RX default buffer size. This is the expected buffer size
 		that should be returned on a `read()` operation.
 
+config RMT_LOOP_TEST_MODE
+	bool "RMT character driver loopback test mode (for testing only)"
+	depends on EXPERIMENTAL
+	default n
+	---help---
+		This enables a lower-half driver-specific loopback test
+		mode that attaches the transmitter to the receiver, being
+		able to test the RMT peripheral without any external
+		connection. This feature depends on lower-half driver
+		implementation.
+
 endif # RMT