diff --git a/FluxEngine.cydsn/main.c b/FluxEngine.cydsn/main.c
index 5785321..5ac26c9 100644
--- a/FluxEngine.cydsn/main.c
+++ b/FluxEngine.cydsn/main.c
@@ -14,12 +14,13 @@
 #define STEP_TOWARDS0 1
 #define STEP_AWAYFROM0 0
 
-static uint32_t clock = 0;
+static volatile uint32_t clock = 0;
+static volatile bool index_irq = false;
+
 static bool motor_on = false;
 static uint32_t motor_on_time = 0;
 static bool homed = false;
 static int current_track = 0;
-static volatile bool index_irq = false;
 
 #if 0
 static uint8_t td[BUFFER_COUNT];
@@ -107,10 +108,15 @@ CY_ISR(dma_finished_isr)
 }
 #endif
 
+static void wait_until_writeable(int ep)
+{
+    while (USBFS_GetEPState(ep) != USBFS_IN_BUFFER_EMPTY)
+        ;
+}
+
 static void send_reply(struct any_frame* f)
 {
-    while (USBFS_GetEPState(FLUXENGINE_CMD_IN_EP_NUM) != USBFS_IN_BUFFER_EMPTY)
-        ;
+    wait_until_writeable(FLUXENGINE_CMD_IN_EP_NUM);
     USBFS_LoadInEP(FLUXENGINE_CMD_IN_EP_NUM, (uint8_t*) f, f->f.size);
 }
 
@@ -172,23 +178,41 @@ static void cmd_measure_speed(struct any_frame* f)
 {
     start_motor();
     
-    UART_PutString("wait for index\n");
     index_irq = false;
     while (!index_irq)
         ;
     index_irq = false;
     int start_clock = clock;
-    UART_PutString("wait for another index\n");
     while (!index_irq)
         ;
     int end_clock = clock;
-    UART_PutString("done\n");
     
     DECLARE_REPLY_FRAME(struct speed_frame, F_FRAME_MEASURE_SPEED_REPLY);
     r.period_ms = end_clock - start_clock;
     send_reply((struct any_frame*) &r);    
 }
 
+static void cmd_bulk_test(struct any_frame* f)
+{
+    uint8_t buffer[64];
+    
+    for (int x=0; x<16; x++)
+        for (int y=0; y<256; y++)
+        {
+            for (unsigned z=0; z<sizeof(buffer); z++)
+                buffer[z] = x+y+z;
+                
+            wait_until_writeable(FLUXENGINE_DATA_IN_EP_NUM);
+            USBFS_LoadInEP(FLUXENGINE_DATA_IN_EP_NUM, buffer, sizeof(buffer));
+        }
+    
+    wait_until_writeable(FLUXENGINE_DATA_IN_EP_NUM);
+    USBFS_LoadInEP(FLUXENGINE_DATA_IN_EP_NUM, NULL, 0);
+    
+    DECLARE_REPLY_FRAME(struct any_frame, F_FRAME_BULK_TEST_REPLY);
+    send_reply(&r);
+}
+
 static void handle_command(void)
 {
     static uint8_t input_buffer[FRAME_SIZE];
@@ -210,6 +234,10 @@ static void handle_command(void)
             cmd_measure_speed(f);
             break;
             
+        case F_FRAME_BULK_TEST_CMD:
+            cmd_bulk_test(f);
+            break;
+            
         default:
             send_error(F_ERROR_BAD_COMMAND);
     }
@@ -256,9 +284,14 @@ int main(void)
             UART_PutString("USB ready\r");
             //CyDmaChEnable(dma_channel, true);
             USBFS_EnableOutEP(FLUXENGINE_CMD_OUT_EP_NUM);
+            USBFS_EnableOutEP(FLUXENGINE_DATA_OUT_EP_NUM);
         }
         
         if (USBFS_GetEPState(FLUXENGINE_CMD_OUT_EP_NUM) == USBFS_OUT_BUFFER_FULL)
+        {
+            UART_PutString("incoming USB command\r");
             handle_command();
+            USBFS_EnableOutEP(FLUXENGINE_CMD_OUT_EP);
+        }
     }
 }
diff --git a/globals.h b/globals.h
index 50eced8..23e4101 100644
--- a/globals.h
+++ b/globals.h
@@ -13,6 +13,7 @@
 #include "protocol.h"
 
 extern void error(const char* message, ...);
+extern double gettime(void);
 
 extern void usb_init(void);
 extern void usb_cmd_send(void* ptr, int len);
@@ -21,5 +22,6 @@ extern void usb_cmd_recv(void* ptr, int len);
 extern int usb_get_version(void);
 extern void usb_seek(int track);
 extern int usb_measure_speed(void);
+extern void usb_bulk_test(void);
 
 #endif
diff --git a/main.c b/main.c
index 4150911..ed4c9e7 100644
--- a/main.c
+++ b/main.c
@@ -51,6 +51,8 @@ int main(int argc, char* const* argv)
 	int period_ms = usb_measure_speed();
 	printf("Rotational period is %d ms (%f rpm)\n", period_ms, 60000.0/period_ms);
 
+	usb_bulk_test();
+
 	#if 0
 	parse_options(argc, argv);
 	if (!serialport)
diff --git a/protocol.h b/protocol.h
index 9f25278..8707d6c 100644
--- a/protocol.h
+++ b/protocol.h
@@ -32,6 +32,8 @@ enum
     F_FRAME_SEEK_REPLY,           /* any_frame */
     F_FRAME_MEASURE_SPEED_CMD,    /* any_frame */
     F_FRAME_MEASURE_SPEED_REPLY,  /* speed_frame */
+    F_FRAME_BULK_TEST_CMD,        /* any_frame */
+    F_FRAME_BULK_TEST_REPLY,      /* any_frame */
 };
 
 enum
diff --git a/usb.c b/usb.c
index ae1120c..7ffd647 100644
--- a/usb.c
+++ b/usb.c
@@ -97,3 +97,42 @@ int usb_measure_speed(void)
     return r->period_ms;
 }
 
+static void large_bulk_transfer(int ep, void* buffer, int total_len)
+{
+    int count = 0;
+    while (count < total_len)
+    {
+        int len = total_len - count;
+        int i = libusb_bulk_transfer(device, ep,
+            ((uint8_t*)buffer)+count, len, &len, TIMEOUT);
+        if (i < 0)
+            error("data transfer failed: %s", libusb_strerror(i));
+        count += len;
+    }
+}
+
+void usb_bulk_test(void)
+{
+    struct any_frame f = { .f = {.type = F_FRAME_BULK_TEST_CMD, .size = sizeof(f)} };
+    usb_cmd_send(&f, f.f.size);
+
+    uint8_t bulk_buffer[16*256*64];
+    int total_len = sizeof(bulk_buffer);
+    double start_time = gettime();
+    large_bulk_transfer(FLUXENGINE_DATA_IN_EP, bulk_buffer, total_len);
+    double elapsed_time = gettime() - start_time;
+
+    printf("Transferred %d bytes in %d ms (%d kB/s)\n",
+        total_len, (int)(elapsed_time * 1000.0),
+        (int)((total_len / 1024.0) / elapsed_time));
+    for (int x=0; x<16; x++)
+        for (int y=0; y<256; y++)
+            for (int z=0; z<64; z++)
+            {
+                int offset = x*16384 + y*64 + z;
+                if (bulk_buffer[offset] != (uint8_t)(x+y+z))
+                    error("data transfer corrupted at 0x%x (%d.%d.%d)", offset, x, y, z);
+            }
+
+    await_reply(F_FRAME_BULK_TEST_REPLY);
+}