I think this is pretty much completed for the rp2xxx with the radio 2 module. I'll add support for a few others next.

CMakeLists.txt

@@ -15,7 +15,7 @@ add_compile_definitions(PICO_RP2350A=0)
 
 pico_sdk_init()
 
-set(CS_MIDI_HID_MOUSE ON CACHE BOOL "" FORCE)
+set(CS_MIDI_HID_KEYBOARD ON CACHE BOOL "" FORCE)
 add_subdirectory(lib/cs-midi)
 
 # cs_midi's BTstack sources need project-level btstack_config.h and lwipopts.h
@@ -33,8 +33,8 @@ target_include_directories(fractional_looper PRIVATE
 
 target_compile_definitions(fractional_looper PRIVATE
     PICO_STDIO_USB_STDOUT_TIMEOUT_US=0
-    PICO_DEFAULT_UART_TX_PIN=12
+    # PICO_DEFAULT_UART_TX_PIN=12
-    PICO_DEFAULT_UART_RX_PIN=13
+    # PICO_DEFAULT_UART_RX_PIN=13
 )
 
 target_link_libraries(fractional_looper
@@ -48,7 +48,7 @@ target_link_libraries(fractional_looper
     cs_midi
 )
 
-pico_enable_stdio_usb(fractional_looper 0)
+pico_enable_stdio_usb(fractional_looper 1)
-pico_enable_stdio_uart(fractional_looper 1)
+pico_enable_stdio_uart(fractional_looper 0)
 
 pico_add_extra_outputs(fractional_looper)

lib/cs-midi

@@ -1 +1 @@
-Subproject commit 517cbbb3180bc446ac919f7e787f8df10d90cbc0
+Subproject commit 2187943124823e896b67084dbe8b2e87be2165ec

main.cpp

@@ -1,6 +1,7 @@
 #include <cstdio>
 #include "pico/stdlib.h"
 #include "pico/cyw43_arch.h"
+#include "hardware/adc.h"
 #include <cs_midi.h>
 #include "spp_midi.h"
 
@@ -45,6 +46,37 @@ void apply_map(const CCMap &m) {
     btn4.setAddressUnsafe({m.btn[2], Channel_1});
 }
 
+constexpr float BATT_V_MIN = 3.0f;
+constexpr float BATT_V_MAX = 4.2f;
+constexpr uint32_t BATT_INTERVAL_MS = 60000;
+constexpr uint32_t BATT_SETTLE_MS  = 200;
+constexpr uint BATT_SINK_PIN = 41;
+constexpr uint BATT_ADC_INPUT = 2; // GP42 = ADC2
+
+enum BattState { BATT_IDLE, BATT_SETTLING };
+BattState batt_state = BATT_IDLE;
+uint32_t  batt_timer = 0;
+
+void batt_sink_enable() {
+    gpio_put(BATT_SINK_PIN, 0);
+    gpio_set_dir(BATT_SINK_PIN, GPIO_OUT);
+}
+
+void batt_sink_float() {
+    gpio_set_dir(BATT_SINK_PIN, GPIO_IN);
+    gpio_disable_pulls(BATT_SINK_PIN);
+}
+
+uint8_t read_battery_percent() {
+    adc_select_input(BATT_ADC_INPUT);
+    uint16_t raw = adc_read();
+    float voltage = raw * (3.3f / 4096.0f) * 2.0f;
+    float pct = (voltage - BATT_V_MIN) / (BATT_V_MAX - BATT_V_MIN) * 100.0f;
+    if (pct < 0.0f) pct = 0.0f;
+    if (pct > 100.0f) pct = 100.0f;
+    return static_cast<uint8_t>(pct);
+}
+
 int main() {
     stdio_init_all();
     if (cyw43_arch_init()) {
@@ -52,6 +84,11 @@ int main() {
         return 1;
     }
 
+    adc_init();
+    adc_gpio_init(42);
+    gpio_init(BATT_SINK_PIN);
+    batt_sink_float();
+
     RelativeCCSender::setMode(relativeCCmode::MACKIE_CONTROL_RELATIVE);
     ble_midi.setName("FractionalLooper");
     Control_Surface.begin();
@@ -67,6 +104,25 @@ int main() {
             apply_map(maps[state]);
         }
 
+        uint32_t now = to_ms_since_boot(get_absolute_time());
+        switch (batt_state) {
+        case BATT_IDLE:
+            if (now - batt_timer >= BATT_INTERVAL_MS) {
+                batt_sink_enable();
+                batt_timer = now;
+                batt_state = BATT_SETTLING;
+            }
+            break;
+        case BATT_SETTLING:
+            if (now - batt_timer >= BATT_SETTLE_MS) {
+                setBLEBatteryLevel(read_battery_percent());
+                batt_sink_float();
+                batt_timer = now;
+                batt_state = BATT_IDLE;
+            }
+            break;
+        }
+
         sleep_ms(1);
     }
 }