doc: document project

README.md

@@ -1,9 +1,48 @@
-this is a template firmware for [ESP32-S2](https://www.espressif.com/en/products/socs/esp32-s2)-based micro-controller projects.
+this project is about interfacing the GM-1352 sound level meter using an ESP32-S2-based board, so to read the sound level measurements digitally.
+
+GM-1352
+=======
+
+the GM-1352 is the successor of the GM-1351, and very similar to it.
+the main difference is that the power is not delivered by a 9V battery, but by 3x1.5V AA batteries.
+
+[CuVoodoo #030](https://www.cuvoodoo.info/cuvoodoo-030-audio-is-killing-the-music/) already explained how to interface it.
+basically just tap on the lines between the MCU (a EFM8BB10F8G-QFN20) and LCD controller (a Chip-on-Board under a blob of epoxy).
+there are test points available for that:
+
+- CS: chip select, to start data communication
+- DATA: the actual data bits
+- WR: the data clock (not periodic)
+
+there are additional test points to read (or assert) button presses:
+
+- 1: HOLD button (press low)
+- 2: MIN/MAX button (press low)
+- 3: POWER button (press low)
+
+there is another test point marked S, but I don't know what this is for.
+
+also note that the LCD has segments for Bluetooth and USB.
+there might be variants of the GM-1352 with these options.
 
 board
 =====
 
-the board used is a [WEMOS](https://www.wemos.cc/en/latest/index.html) [S2 mini](https://www.wemos.cc/en/latest/s2/s2_mini.html).
+this repository is the firmware for [ESP32-S2](https://www.espressif.com/en/products/socs/esp32-s2)-based [WEMOS](https://www.wemos.cc/en/latest/index.html) [S2 mini](https://www.wemos.cc/en/latest/s2/s2_mini.html) board.
+
+connect the GM-1352 to the S2 mini as follows:
+
+- B+ to 5V: to power or get power from the device
+- B- to GND: ground reference
+- POWER to 16: to wake up the S2 when the device is powered (the S2 will shut down shortly after the GM-1352)
+- DATA to 18: this will be the SPI MOSI line to read the measurments
+- CS to 33: this will be the SPI CS line to identify transactions
+- WR to 35: this will be the SPI SCK line to clock the data bits (not periodic)
+
+I soldered wires to the pads, and broke them out on a 8-pin female header, located above the battery compartment.
+this also to easily connect on row of the S2 mini to it on the back of the GM-1352.
+
+now you can power the sound level meter through the S2 mini USB port, and read the measurements over its serial CDC ACM interface.
 
 compile and flash
 =================

main/main.c

@@ -3,9 +3,11 @@
  */
 #include <stdio.h>
 #include <stdlib.h>
+#include <unistd.h>
 #include <sys/reent.h>
 #include "esp_log.h"
 #include "esp_mac.h"
+#include "esp_sleep.h"
 
 #include "freertos/FreeRTOS.h"
 #include "freertos/task.h"
@@ -28,19 +30,14 @@
 // GPIO for on-board LED (WEMOS S2 mini, source on)
 #define LED_BOARD 15
 
-/* GM1352 test pads:
- * - CS: LCD chip select, to start data communication
- * - DATA: LCD data bits
- * - WR: LCD data clock (not periodic)
- * - S: ??? (low)
- * - 1: HOLD button (press low)
- * - 2: MIN/MAX button (press low)
- * - 3: POWER button (press low)
- */
-#define GPIO_POWER (35U)
-#define GPIO_MOSI (16U)
-#define GPIO_SCLK (33U)
-#define GPIO_CS (18U)
+// connect GPIO to test pad 3
+#define GPIO_POWER (16U)
+// connect GPIO to test pad DATA
+#define GPIO_MOSI (18U)
+// connect GPIO to test pad WR
+#define GPIO_SCLK (35U)
+// connect GPIO to test pad CS
+#define GPIO_CS (33U)
 
 static const char *TAG = "main";
 
@@ -283,6 +280,16 @@ void app_main(void)
 	ESP_ERROR_CHECK( tusb_dfu_rf_init() ); // configure DFU runtime (ensures we can use it)
 	ESP_LOGI(TAG, "USB initialized");
 
+	// configure shutdown
+	io_conf.pin_bit_mask = (1ULL << GPIO_POWER); // GPIO to configure
+	io_conf.intr_type = GPIO_INTR_DISABLE; // disable interrupt
+	io_conf.mode = GPIO_MODE_INPUT; // set as input
+	io_conf.pull_down_en = 0; // don't use pull-down
+	io_conf.pull_up_en = 0; // there is already an external pull-up
+	ESP_ERROR_CHECK( gpio_config(&io_conf) ); // configure GPIO
+	ESP_ERROR_CHECK( esp_sleep_disable_wakeup_source(ESP_SLEEP_WAKEUP_ALL) ); // make sure all sources are disabled
+	ESP_ERROR_CHECK( esp_sleep_enable_ext0_wakeup(GPIO_POWER, 0) ); // use power button to wake up (low when pressed)
+
 	// task to decode and show the measurements
 	meas_queue = xQueueCreate(MEAS_QUEUE_SIZE, sizeof(spi_slave_transaction_t));
 	ESP_ERROR_CHECK( NULL == meas_queue );
@@ -323,5 +330,19 @@ void app_main(void)
 		} else {
 			gpio_set_level(LED_BOARD, 1);
 		}
+
+		if (timeout > 0) {
+			printf(".");
+			fflush(stdout);
+			fsync(fileno(stdout));
+		}
+		timeout++;
+		if (timeout > 10) {
+			printf("\nshutting down due to inactivity\n");
+			fflush(stdout);
+			fsync(fileno(stdout));
+			gpio_set_level(LED_BOARD, 1); // ensure run LED is off
+			esp_deep_sleep_start(); // go to deep sleep
+		}
 	}
 }