samples: drivers: i2s: echo: add MAX32655 support

- reduced block length from 100ms to 33.33ms to compile for low ram
- add compile time conditional option to slave mode
- add overlay file for max32655fthr

Signed-off-by: Anuj Pathak <[email protected]>

Author: cx-anuj-pathak

samples/drivers/i2s/echo/boards/max32655fthr_max32655_m4.overlay

@@ -0,0 +1,16 @@
+/*
+ * Copyright (c) 2025 Croxel Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+i2s_rxtx: &i2s0 {
+	status = "okay";
+};
+
+&i2c1 {
+	max9867: max9867@18 {
+		compatible = "adi,max9867";
+		reg = <0x18>;
+	};
+};

samples/drivers/i2s/echo/src/main.c

@@ -21,12 +21,19 @@
 #define I2S_TX_NODE  DT_NODELABEL(i2s_tx)
 #endif
 
+/* Reduce echo delay when running on low ram devices */
+#if CONFIG_SRAM_SIZE <= 48
+#define ECHO_DELAY 30
+#else
+#define ECHO_DELAY 10
+#endif
+
 #define SAMPLE_FREQUENCY    44100
 #define SAMPLE_BIT_WIDTH    16
 #define BYTES_PER_SAMPLE    sizeof(int16_t)
 #define NUMBER_OF_CHANNELS  2
-/* Such block length provides an echo with the delay of 100 ms. */
-#define SAMPLES_PER_BLOCK   ((SAMPLE_FREQUENCY / 10) * NUMBER_OF_CHANNELS)
+/* Such block length provides an echo with the delay of 100ms or 33.33ms */
+#define SAMPLES_PER_BLOCK   ((SAMPLE_FREQUENCY / ECHO_DELAY) * NUMBER_OF_CHANNELS)
 #define INITIAL_BLOCKS      2
 #define TIMEOUT             1000
 
@@ -298,7 +305,15 @@ int main(void)
 	config.word_size = SAMPLE_BIT_WIDTH;
 	config.channels = NUMBER_OF_CHANNELS;
 	config.format = I2S_FMT_DATA_FORMAT_I2S;
+	/*
+	 * On MAX32655FTHR, MAX9867 MCLK is connected to external 12.2880 crystal
+	 * thus using slave mode
+	 */
+#if CONFIG_BOARD_MAX32655FTHR_MAX32655_M4
+	config.options = I2S_OPT_BIT_CLK_SLAVE | I2S_OPT_FRAME_CLK_SLAVE;
+#else
 	config.options = I2S_OPT_BIT_CLK_MASTER | I2S_OPT_FRAME_CLK_MASTER;
+#endif
 	config.frame_clk_freq = SAMPLE_FREQUENCY;
 	config.mem_slab = &mem_slab;
 	config.block_size = BLOCK_SIZE;