diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5478126..a489cef 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -4,33 +4,27 @@ on:
   - push
   - pull_request
 
-jobs:
-  CI:
-    runs-on: ubuntu-22.04
-    steps:
-      - name: 'Check out code'
-        uses: actions/checkout@v4
+env:
+  DEFAULT_PYTHON: 3.9
 
-      - name: 'Install dependencies'
+jobs:
+  pico:
+    name: RPi Pico compilation
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Check out code from GitHub
+        uses: actions/checkout@v2
+
+      - name: Install dependencies
         run: |
           sudo apt-get install cmake gcc-arm-none-eabi libnewlib-arm-none-eabi
 
-      - name: 'Update Submodules'
+      - name: Generate RPi Pico binaries
         run: |
-          git submodule sync --recursive
-          git submodule update --init --recursive
+          ./build.sh
 
-      - name: 'Configure'
-        run: |
-          mkdir -p build
-          cmake -B build
-
-      - name: 'Build'
-        run: |
-          make -C build
-
-      - name: 'Upload binary'
-        uses: actions/upload-artifact@v4
+      - name: 'Upload RPi Pico binary'
+        uses: actions/upload-artifact@v2
         with:
           name: pico-uart-bridge.uf2
           path: build/uart_bridge.uf2
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 881c3f6..eda4f18 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -7,7 +7,7 @@ include(pico-sdk/pico_sdk_init.cmake)
 project(pico_uart_bridge)
 
 pico_sdk_init()
-
+  
 add_executable(uart_bridge uart-bridge.c usb-descriptors.c)
 
 target_include_directories(uart_bridge PUBLIC
@@ -15,7 +15,6 @@ target_include_directories(uart_bridge PUBLIC
 	pico-sdk/lib/tinyusb/src)
 
 target_link_libraries(uart_bridge
-	hardware_flash
 	pico_multicore
 	pico_stdlib
 	tinyusb_device)
diff --git a/README.md b/README.md
index 8c5d87d..c6a3967 100644
--- a/README.md
+++ b/README.md
@@ -13,7 +13,7 @@ Raspberry Pi Pico Pinout
 
 | Raspberry Pi Pico GPIO | Function |
 |:----------------------:|:--------:|
-| GPIO16 (Pin 21)        | UART0 TX |
-| GPIO17 (Pin 22)        | UART0 RX |
+| GPIO0 (Pin 1)          | UART0 TX |
+| GPIO1 (Pin 2)          | UART0 RX |
 | GPIO4 (Pin 6)          | UART1 TX |
 | GPIO5 (Pin 7)          | UART1 RX |
diff --git a/build.sh b/build.sh
index c361db0..a88b320 100755
--- a/build.sh
+++ b/build.sh
@@ -1,17 +1,21 @@
-#!/bin/bash
+#!/bin/sh
 
-BASE_DIR="$(dirname ${BASH_SOURCE[0]})"
-BUILD_DIR=$BASE_DIR/build
-PICO_SDK_DIR=$BASE_DIR/pico-sdk
+BUILD_DIR=build
+PICO_SDK_DIR=pico-sdk
+
+main () {
+	local cur_dir=$PWD
 
-main() {
 	if [ ! -d "$PICO_SDK_DIR/.git" ]; then
-		git submodule sync --recursive
 		git submodule update --init --recursive
 	fi
 
-	cmake -B $BUILD_DIR -S $BASE_DIR
-	make -C $BUILD_DIR
+	mkdir -p $BUILD_DIR
+	cd $BUILD_DIR
+	cmake ../
+	make
+
+	cd $cur_dir
 }
 
 main $@
diff --git a/pico-sdk b/pico-sdk
index 6a7db34..2d5789e 160000
--- a/pico-sdk
+++ b/pico-sdk
@@ -1 +1 @@
-Subproject commit 6a7db34ff63345a7badec79ebea3aaef1712f374
+Subproject commit 2d5789eca89658a7f0a01e2d6010c0f254605d72
diff --git a/tusb_config.h b/tusb_config.h
index 80eeb52..7e0ec54 100644
--- a/tusb_config.h
+++ b/tusb_config.h
@@ -13,9 +13,7 @@
 #define CFG_TUSB_RHPORT0_MODE OPT_MODE_DEVICE
 
 #define CFG_TUD_CDC 2
-#define CFG_TUD_CDC_RX_BUFSIZE 1024
-#define CFG_TUD_CDC_TX_BUFSIZE 1024
-
-void usbd_serial_init(void);
+#define CFG_TUD_CDC_RX_BUFSIZE 256
+#define CFG_TUD_CDC_TX_BUFSIZE 256
 
 #endif /* _TUSB_CONFIG_H_ */
diff --git a/uart-bridge.c b/uart-bridge.c
index c4e0805..8bdd592 100644
--- a/uart-bridge.c
+++ b/uart-bridge.c
@@ -17,7 +17,7 @@
 
 #define LED_PIN 25
 
-#define BUFFER_SIZE 2560
+#define BUFFER_SIZE 64
 
 #define DEF_BIT_RATE 115200
 #define DEF_STOP_BITS 1
@@ -26,8 +26,6 @@
 
 typedef struct {
 	uart_inst_t *const inst;
-	uint irq;
-	void *irq_fn;
 	uint8_t tx_pin;
 	uint8_t rx_pin;
 } uart_id_t;
@@ -44,20 +42,13 @@ typedef struct {
 	mutex_t usb_mtx;
 } uart_data_t;
 
-void uart0_irq_fn(void);
-void uart1_irq_fn(void);
-
 const uart_id_t UART_ID[CFG_TUD_CDC] = {
 	{
 		.inst = uart0,
-		.irq = UART0_IRQ,
-		.irq_fn = &uart0_irq_fn,
-		.tx_pin = 16,
-		.rx_pin = 17,
+		.tx_pin = 0,
+		.rx_pin = 1,
 	}, {
 		.inst = uart1,
-		.irq = UART1_IRQ,
-		.irq_fn = &uart1_irq_fn,
 		.tx_pin = 4,
 		.rx_pin = 5,
 	}
@@ -128,18 +119,19 @@ void update_uart_cfg(uint8_t itf)
 	mutex_exit(&ud->lc_mtx);
 }
 
-void usb_read_bytes(uint8_t itf)
-{
-	uart_data_t *ud = &UART_DATA[itf];
+void usb_read_bytes(uint8_t itf) {
 	uint32_t len = tud_cdc_n_available(itf);
 
-	if (len &&
-	    mutex_try_enter(&ud->usb_mtx, NULL)) {
+	if (len) {
+		uart_data_t *ud = &UART_DATA[itf];
+
+		mutex_enter_blocking(&ud->usb_mtx);
+
 		len = MIN(len, BUFFER_SIZE - ud->usb_pos);
 		if (len) {
 			uint32_t count;
 
-			count = tud_cdc_n_read(itf, &ud->usb_buffer[ud->usb_pos], len);
+			count = tud_cdc_n_read(itf, ud->usb_buffer, len);
 			ud->usb_pos += count;
 		}
 
@@ -147,17 +139,17 @@ void usb_read_bytes(uint8_t itf)
 	}
 }
 
-void usb_write_bytes(uint8_t itf)
-{
+void usb_write_bytes(uint8_t itf) {
 	uart_data_t *ud = &UART_DATA[itf];
 
-	if (ud->uart_pos &&
-	    mutex_try_enter(&ud->uart_mtx, NULL)) {
+	if (ud->uart_pos) {
 		uint32_t count;
 
+		mutex_enter_blocking(&ud->uart_mtx);
+
 		count = tud_cdc_n_write(itf, ud->uart_buffer, ud->uart_pos);
 		if (count < ud->uart_pos)
-			memmove(ud->uart_buffer, &ud->uart_buffer[count],
+			memcpy(ud->uart_buffer, &ud->uart_buffer[count],
 			       ud->uart_pos - count);
 		ud->uart_pos -= count;
 
@@ -189,7 +181,7 @@ void core1_entry(void)
 		int con = 0;
 
 		tud_task();
-
+	
 		for (itf = 0; itf < CFG_TUD_CDC; itf++) {
 			if (tud_cdc_n_connected(itf)) {
 				con = 1;
@@ -201,16 +193,16 @@ void core1_entry(void)
 	}
 }
 
-static inline void uart_read_bytes(uint8_t itf)
-{
-	uart_data_t *ud = &UART_DATA[itf];
+void uart_read_bytes(uint8_t itf) {
 	const uart_id_t *ui = &UART_ID[itf];
 
 	if (uart_is_readable(ui->inst)) {
+		uart_data_t *ud = &UART_DATA[itf];
+
 		mutex_enter_blocking(&ud->uart_mtx);
 
 		while (uart_is_readable(ui->inst) &&
-		       (ud->uart_pos < BUFFER_SIZE)) {
+			ud->uart_pos < BUFFER_SIZE) {
 			ud->uart_buffer[ud->uart_pos] = uart_getc(ui->inst);
 			ud->uart_pos++;
 		}
@@ -219,42 +211,22 @@ static inline void uart_read_bytes(uint8_t itf)
 	}
 }
 
-void uart0_irq_fn(void)
-{
-	uart_read_bytes(0);
-}
-
-void uart1_irq_fn(void)
-{
-	uart_read_bytes(1);
-}
-
-void uart_write_bytes(uint8_t itf)
-{
+void uart_write_bytes(uint8_t itf) {
 	uart_data_t *ud = &UART_DATA[itf];
 
-	if (ud->usb_pos &&
-	    mutex_try_enter(&ud->usb_mtx, NULL)) {
+	if (ud->usb_pos) {
 		const uart_id_t *ui = &UART_ID[itf];
-		uint32_t count = 0;
 
-		while (uart_is_writable(ui->inst) &&
-		       count < ud->usb_pos) {
-			uart_putc_raw(ui->inst, ud->usb_buffer[count]);
-			count++;
-		}
+		mutex_enter_blocking(&ud->usb_mtx);
 
-		if (count < ud->usb_pos)
-			memmove(ud->usb_buffer, &ud->usb_buffer[count],
-			       ud->usb_pos - count);
-		ud->usb_pos -= count;
+		uart_write_blocking(ui->inst, ud->usb_buffer, ud->usb_pos);
+		ud->usb_pos = 0;
 
 		mutex_exit(&ud->usb_mtx);
 	}
 }
 
-void init_uart_data(uint8_t itf)
-{
+void init_uart_data(uint8_t itf) {
 	const uart_id_t *ui = &UART_ID[itf];
 	uart_data_t *ud = &UART_DATA[itf];
 
@@ -289,20 +261,12 @@ void init_uart_data(uint8_t itf)
 	uart_set_format(ui->inst, databits_usb2uart(ud->usb_lc.data_bits),
 			stopbits_usb2uart(ud->usb_lc.stop_bits),
 			parity_usb2uart(ud->usb_lc.parity));
-	uart_set_fifo_enabled(ui->inst, false);
-
-	/* UART RX Interrupt */
-	irq_set_exclusive_handler(ui->irq, ui->irq_fn);
-	irq_set_enabled(ui->irq, true);
-	uart_set_irq_enables(ui->inst, true, false);
 }
 
 int main(void)
 {
 	int itf;
 
-	usbd_serial_init();
-
 	for (itf = 0; itf < CFG_TUD_CDC; itf++)
 		init_uart_data(itf);
 
@@ -314,6 +278,7 @@ int main(void)
 	while (1) {
 		for (itf = 0; itf < CFG_TUD_CDC; itf++) {
 			update_uart_cfg(itf);
+			uart_read_bytes(itf);
 			uart_write_bytes(itf);
 		}
 	}
diff --git a/usb-descriptors.c b/usb-descriptors.c
index 738f9d0..5c10798 100644
--- a/usb-descriptors.c
+++ b/usb-descriptors.c
@@ -9,7 +9,6 @@
  * Copyright (c) 2019 Damien P. George
  */
 
-#include <hardware/flash.h>
 #include <tusb.h>
 
 #define DESC_STR_MAX 20
@@ -18,21 +17,18 @@
 #define USBD_PID 0x000A /* Raspberry Pi Pico SDK CDC */
 
 #define USBD_DESC_LEN (TUD_CONFIG_DESC_LEN + TUD_CDC_DESC_LEN * CFG_TUD_CDC)
-#define USBD_MAX_POWER_MA 500
+#define USBD_MAX_POWER_MA 250
 
 #define USBD_ITF_CDC_0 0
 #define USBD_ITF_CDC_1 2
 #define USBD_ITF_MAX 4
 
 #define USBD_CDC_0_EP_CMD 0x81
-#define USBD_CDC_1_EP_CMD 0x83
-
-#define USBD_CDC_0_EP_OUT 0x01
-#define USBD_CDC_1_EP_OUT 0x03
-
+#define USBD_CDC_1_EP_CMD 0x84
+#define USBD_CDC_0_EP_OUT 0x02
+#define USBD_CDC_1_EP_OUT 0x05
 #define USBD_CDC_0_EP_IN 0x82
-#define USBD_CDC_1_EP_IN 0x84
-
+#define USBD_CDC_1_EP_IN 0x85
 #define USBD_CDC_CMD_MAX_SIZE 8
 #define USBD_CDC_IN_OUT_MAX_SIZE 64
 
@@ -40,7 +36,6 @@
 #define USBD_STR_MANUF 0x01
 #define USBD_STR_PRODUCT 0x02
 #define USBD_STR_SERIAL 0x03
-#define USBD_STR_SERIAL_LEN 17
 #define USBD_STR_CDC 0x04
 
 static const tusb_desc_device_t usbd_desc_device = {
@@ -73,12 +68,10 @@ static const uint8_t usbd_desc_cfg[USBD_DESC_LEN] = {
 		USBD_CDC_IN_OUT_MAX_SIZE),
 };
 
-static char usbd_serial[USBD_STR_SERIAL_LEN] = "000000000000";
-
 static const char *const usbd_desc_str[] = {
 	[USBD_STR_MANUF] = "Raspberry Pi",
 	[USBD_STR_PRODUCT] = "Pico",
-	[USBD_STR_SERIAL] = usbd_serial,
+	[USBD_STR_SERIAL] = "000000000000",
 	[USBD_STR_CDC] = "Board CDC",
 };
 
@@ -102,7 +95,6 @@ const uint16_t *tud_descriptor_string_cb(uint8_t index, uint16_t langid)
 		len = 1;
 	} else {
 		const char *str;
-		char serial[USBD_STR_SERIAL_LEN];
 
 		if (index >= sizeof(usbd_desc_str) / sizeof(usbd_desc_str[0]))
 			return NULL;
@@ -116,13 +108,3 @@ const uint16_t *tud_descriptor_string_cb(uint8_t index, uint16_t langid)
 
 	return desc_str;
 }
-
-void usbd_serial_init(void)
-{
-	uint8_t id[8];
-
-	flash_get_unique_id(id);
-
-	snprintf(usbd_serial, USBD_STR_SERIAL_LEN, "%02X%02X%02X%02X%02X%02X%02X%02X",
-		 id[0], id[1], id[2], id[3], id[4], id[5], id[6], id[7]);
-}