diff --git a/include/time.h b/include/time.h
new file mode 100644
index 0000000..3408390
--- /dev/null
+++ b/include/time.h
@@ -0,0 +1,15 @@
+#ifndef __TIME_H
+#define __TIME_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void time_init(void);
+int elapsed(int *last_event, int period);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __TIME_H */
diff --git a/input/top.bin b/input/top.bin
index 1407640..53450bd 100644
Binary files a/input/top.bin and b/input/top.bin differ
diff --git a/src/main.c b/src/main.c
index 43eb542..4635b5a 100644
--- a/src/main.c
+++ b/src/main.c
@@ -3,46 +3,189 @@
 #include <printf.h>
 #include <uart.h>
 #include <usb.h>
+#include <time.h>
 
 #include <generated/csr.h>
 
-void isr(void) {
+enum usb_responses {
+    USB_STALL = 0b11,
+    USB_ACK   = 0b00,
+    USB_NAK   = 0b01,
+    USB_NONE  = 0b10,
+};
+
+void isr(void)
+{
     unsigned int irqs;
-    
+
     irqs = irq_pending() & irq_getmask();
-    
-//    if (irqs & (1 << USB_INTERRUPT))
-//        usb_isr();
+
+    if (irqs & (1 << USB_INTERRUPT))
+        usb_isr();
 
     if (irqs & (1 << UART_INTERRUPT))
         uart_isr();
 }
 
-static void rv_putchar(void *ignored, char c) {
+static void rv_putchar(void *ignored, char c)
+{
     (void)ignored;
     uart_write(c);
 }
 
-static void init(void) {
+static void init(void)
+{
     irq_setmask(0);
     irq_setie(1);
     uart_init();
     usb_init();
+    time_init();
     init_printf(NULL, rv_putchar);
 }
 
-int main(int argc, char **argv) {
+static uint32_t read_timer(void)
+{
+    timer0_update_value_write(1);
+    return timer0_value_read();
+}
+
+#ifdef CSR_USB_EP_0_OUT_EV_PENDING_ADDR
+struct usb_status
+{
+    // uint32_t out_ev_status;
+    uint32_t out_ev_pending;
+    uint32_t in_ev_status;
+    uint32_t out_last_tok;
+    uint32_t out_obuf_empty;
+    uint32_t in_ibuf_empty;
+};
+
+static struct usb_status get_status(void)
+{
+    struct usb_status s;
+    // s.out_ev_status = usb_ep_0_out_ev_status_read();
+    s.out_ev_pending = usb_ep_0_out_ev_pending_read();
+    s.in_ev_status = usb_ep_0_in_ev_status_read();
+    s.out_last_tok = usb_ep_0_out_last_tok_read();
+    s.out_obuf_empty = usb_ep_0_out_obuf_empty_read();
+    s.in_ibuf_empty = usb_ep_0_in_ibuf_empty_read();
+    return s;
+}
+
+static void get_print_status(void)
+{
+    static int loops;
+    int obufbuf_cnt = 0;
+    struct usb_status s = get_status();
+
+    // printf("i: %8d  OEP: %02x  OBE: %02x  OLT: %02x\n",
+    //         loops++,
+    //         s.out_ev_pending,
+    //         s.out_obuf_empty,
+    //         s.out_last_tok);
+
+    if (s.out_ev_pending & (1 << 1)) {
+        loops++;
+        uint8_t obufbuf[128];
+        while (!usb_ep_0_out_obuf_empty_read()) {
+            uint32_t obh = usb_ep_0_out_obuf_head_read();
+            obufbuf[obufbuf_cnt++] = obh;
+            usb_ep_0_out_obuf_head_write(1);
+        }
+
+        int i;
+        printf("i: %d  b: %d olt: %02x  --", loops, obufbuf_cnt, s.out_last_tok);//obe: %d  obh: %02x\n", i, obe, obh);
+        for (i = 0; i < obufbuf_cnt; i++) {
+            printf(" %02x", obufbuf[i]);
+        }
+        printf("\n");
+
+        usb_ep_0_out_ev_pending_write((1 << 1));
+
+        // Response
+        if (!usb_ep_0_in_ibuf_empty_read()) {
+            printf("USB ibuf still has data\n");
+            return;
+        }
+
+        uint32_t usb_in_pending = usb_ep_0_out_ev_pending_read();
+        if (usb_in_pending) {
+            printf("USB EP0 in pending is: %02x\n", usb_in_pending);
+            return;
+        }
+
+        for (i = 0; i < 0x20; i++) {
+            usb_ep_0_in_ibuf_head_write(i);
+        }
+        // Indicate that we respond with an ACK
+        usb_ep_0_in_respond_write(USB_ACK);
+        usb_ep_0_in_ev_pending_write(0xff);
+    }
+}
+#else
+static void get_print_status(void)
+{
+    static int loops;
+    uint32_t obe = usb_obuf_empty_read();
+    uint8_t obufbuf[128];
+    int obufbuf_cnt = 0;
+    loops++;
+
+    while (!usb_obuf_empty_read()) {
+        uint32_t obh = usb_obuf_head_read();
+        obufbuf[obufbuf_cnt++] = obh;
+        usb_obuf_head_write(1);
+    }
+    if (obufbuf_cnt) {
+        int i;
+        printf("i: %d  b: %d  --", loops, obufbuf_cnt);//obe: %d  obh: %02x\n", i, obe, obh);
+        for (i = 0; i < obufbuf_cnt; i++) {
+            printf(" %02x", obufbuf[i]);
+        }
+        printf("\n");
+    }
+    // if (!obe) {
+    //     uint32_t obh = usb_obuf_head_read();
+    //     usb_obuf_head_write(1);
+    //     if (i < 300)
+    //         printf("i: %8d  obe: %d  obh: %02x\n", i, obe, obh);
+    // }
+}
+#endif
+
+int main(int argc, char **argv)
+{
     (void)argc;
     (void)argv;
 
     init();
+    printf("\nStatus: %d\n", usb_ep_0_out_ev_pending_read());
+    get_print_status();
+    usb_pullup_out_write(1);
+    usb_ep_0_out_ev_pending_write((1 << 1));
+    printf("Status: %d\n", usb_ep_0_out_obuf_empty_read());
+    get_print_status();
 
     int i = 0;
     printf("Hello, world!\n");
-    while (1) {
-        printf("10 PRINT HELLO, WORLD\n");
-        printf("20 GOTO 10\n");
-        printf("i: %d\n", i++);
+
+    int last_event = 0;
+    while (1)
+    {
+        // unsigned int timer_val_ok = read_timer();
+        // int elapsed(int *last_event, int period)
+        elapsed(&last_event, 1000);
+
+        unsigned int timer_val_cur;
+        // timer_val_cur = read_timer();
+        // printf("10 PRINT HELLO, WORLD\n");
+        // printf("20 GOTO 10\n");
+        // printf("i: %d\n", i++);
+        // timer_val_cur = read_timer();
+        get_print_status();
+        // while (timer0_value_read() != timer_val_ok) {
+        // ;
+        // }
     }
     return 0;
 }
\ No newline at end of file
diff --git a/src/usb.c b/src/usb.c
index 421790d..6a98164 100644
--- a/src/usb.c
+++ b/src/usb.c
@@ -1,5 +1,9 @@
 #include <generated/csr.h>
 
 void usb_init(void) {
-    usb_pullup_out_write(1);
+    // usb_pullup_out_write(1);
+}
+
+void usb_isr(void) {
+
 }
\ No newline at end of file