diff --git a/Makefile b/Makefile
index 8042199..cf57e28 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,7 @@ UNAME           = $(shell uname)
 CFLAGS		= -g -O -Wall -Werror -DVERSION='"$(VERSION).$(GITCOUNT)"'
 LDFLAGS		= -g
 
-OBJS		= main.o util.o radio.o dfu-libusb.o uv380.o md380.o rd5r.o
+OBJS		= main.o util.o radio.o dfu-libusb.o uv380.o md380.o rd5r.o hid.o
 LIBS            = -lusb-1.0
 
 # Linux
diff --git a/Makefile-mingw b/Makefile-mingw
index 4fc387a..6397465 100644
--- a/Makefile-mingw
+++ b/Makefile-mingw
@@ -5,7 +5,7 @@ GITCOUNT        = $(shell git rev-list HEAD --count)
 CFLAGS		= -g -O -Wall -Werror -DVERSION='"$(VERSION).$(GITCOUNT)"'
 LDFLAGS		= -g -s
 
-OBJS		= main.o util.o radio.o dfu-windows.o uv380.o md380.o rd5r.o hid-windows.o
+OBJS		= main.o util.o radio.o dfu-windows.o uv380.o md380.o rd5r.o hid.o hid-windows.o
 LIBS            = -lhid -lsetupapi
 
 # Compiling Windows binary from Linux
diff --git a/hid-libusb.c b/hid-libusb.c
index eb1d52d..3f95335 100644
--- a/hid-libusb.c
+++ b/hid-libusb.c
@@ -32,25 +32,11 @@
 #include <libusb-1.0/libusb.h>
 #include "util.h"
 
-static const unsigned char CMD_PRG[]   = "\2PROGRA";
-static const unsigned char CMD_PRG2[]  = "M\2";
-static const unsigned char CMD_ACK[]   = "A";
-static const unsigned char CMD_READ[]  = "Raan";
-static const unsigned char CMD_WRITE[] = "Waan...";
-static const unsigned char CMD_ENDR[]  = "ENDR";
-static const unsigned char CMD_ENDW[]  = "ENDW";
-static const unsigned char CMD_CWB0[]  = "CWB\4\0\0\0\0";
-static const unsigned char CMD_CWB1[]  = "CWB\4\0\1\0\0";
-
 static libusb_context *ctx = NULL;          // libusb context
 static libusb_device_handle *dev;           // libusb device
 static struct libusb_transfer *transfer;    // async transfer descriptor
 static unsigned char receive_buf[42];       // receive buffer
 static volatile int nbytes_received = 0;    // receive result
-static unsigned offset = 0;                 // CWD offset
-
-#define HID_INTERFACE   0                   // interface index
-#define TIMEOUT_MSEC    500                 // receive timeout
 
 //
 // Callback function for asynchronous receive.
@@ -205,9 +191,8 @@ void hid_send_recv(const unsigned char *data, unsigned nbytes, unsigned char *rd
 //
 // Connect to the specified device.
 // Initiate the programming session.
-// Query and return the device identification string.
 //
-const char *hid_init(int vid, int pid)
+int hid_init(int vid, int pid)
 {
     int error = libusb_init(&ctx);
     if (error < 0) {
@@ -224,7 +209,7 @@ const char *hid_init(int vid, int pid)
         }
         libusb_exit(ctx);
         ctx = 0;
-        return 0;
+        return -1;
     }
     if (libusb_kernel_driver_active(dev, 0)) {
         libusb_detach_kernel_driver(dev, 0);
@@ -239,35 +224,7 @@ const char *hid_init(int vid, int pid)
         ctx = 0;
         exit(-1);
     }
-
-    static unsigned char reply[38];
-    unsigned char ack;
-
-    hid_send_recv(CMD_PRG, 7, &ack, 1);
-    if (ack != CMD_ACK[0]) {
-        fprintf(stderr, "%s: Wrong PRD acknowledge %#x, expected %#x\n",
-            __func__, ack, CMD_ACK[0]);
-        return 0;
-    }
-
-    hid_send_recv(CMD_PRG2, 2, reply, 16);
-
-    hid_send_recv(CMD_ACK, 1, &ack, 1);
-    if (ack != CMD_ACK[0]) {
-        fprintf(stderr, "%s: Wrong PRG2 acknowledge %#x, expected %#x\n",
-            __func__, ack, CMD_ACK[0]);
-        return 0;
-    }
-
-    // Reply:
-    // 42 46 2d 35 52 ff ff ff 56 32 31 30 00 04 80 04
-    //  B  F  -  5  R           V  2  1  0
-
-    // Terminate the string.
-    char *p = memchr(reply, 0xff, sizeof(reply));
-    if (p)
-        *p = 0;
-    return (char*)reply;
+    return 0;
 }
 
 void hid_close()
@@ -284,98 +241,3 @@ void hid_close()
     libusb_exit(ctx);
     ctx = 0;
 }
-
-void hid_read_block(int bno, uint8_t *data, int nbytes)
-{
-    unsigned addr = bno * nbytes;
-    unsigned char ack, cmd[4], reply[32+4];
-    int n;
-
-    if (addr < 0x10000 && offset != 0) {
-        offset = 0;
-        hid_send_recv(CMD_CWB0, 8, &ack, 1);
-        if (ack != CMD_ACK[0]) {
-            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-                __func__, ack, CMD_ACK[0]);
-            exit(-1);
-        }
-    } else if (addr >= 0x10000 && offset == 0) {
-        offset = 0x00010000;
-        hid_send_recv(CMD_CWB1, 8, &ack, 1);
-        if (ack != CMD_ACK[0]) {
-            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-                __func__, ack, CMD_ACK[0]);
-            exit(-1);
-        }
-    }
-
-    for (n=0; n<nbytes; n+=32) {
-        cmd[0] = CMD_READ[0];
-        cmd[1] = (addr + n) >> 8;
-        cmd[2] = addr + n;
-        cmd[3] = 32;
-        hid_send_recv(cmd, 4, reply, sizeof(reply));
-        memcpy(data + n, reply + 4, 32);
-    }
-}
-
-void hid_write_block(int bno, uint8_t *data, int nbytes)
-{
-    unsigned addr = bno * nbytes;
-    unsigned char ack, cmd[4+32];
-    int n;
-
-    if (addr < 0x10000 && offset != 0) {
-        offset = 0;
-        hid_send_recv(CMD_CWB0, 8, &ack, 1);
-        if (ack != CMD_ACK[0]) {
-            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-                __func__, ack, CMD_ACK[0]);
-            exit(-1);
-        }
-    } else if (addr >= 0x10000 && offset == 0) {
-        offset = 0x00010000;
-        hid_send_recv(CMD_CWB1, 8, &ack, 1);
-        if (ack != CMD_ACK[0]) {
-            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-                __func__, ack, CMD_ACK[0]);
-            exit(-1);
-        }
-    }
-
-    for (n=0; n<nbytes; n+=32) {
-        cmd[0] = CMD_WRITE[0];
-        cmd[1] = (addr + n) >> 8;
-        cmd[2] = addr + n;
-        cmd[3] = 32;
-        memcpy(cmd + 4, data + n, 32);
-        hid_send_recv(cmd, 4+32, &ack, 1);
-        if (ack != CMD_ACK[0]) {
-            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-                __func__, ack, CMD_ACK[0]);
-            exit(-1);
-        }
-    }
-}
-
-void hid_read_finish()
-{
-    unsigned char ack;
-
-    hid_send_recv(CMD_ENDR, 4, &ack, 1);
-    if (ack != CMD_ACK[0]) {
-        fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-            __func__, ack, CMD_ACK[0]);
-    }
-}
-
-void hid_write_finish()
-{
-    unsigned char ack;
-
-    hid_send_recv(CMD_ENDW, 4, &ack, 1);
-    if (ack != CMD_ACK[0]) {
-        fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-            __func__, ack, CMD_ACK[0]);
-    }
-}
diff --git a/hid-macos.c b/hid-macos.c
index 8d84cea..823a7a6 100644
--- a/hid-macos.c
+++ b/hid-macos.c
@@ -32,21 +32,10 @@
 #include <IOKit/hid/IOHIDManager.h>
 #include "util.h"
 
-static const unsigned char CMD_PRG[]   = "\2PROGRA";
-static const unsigned char CMD_PRG2[]  = "M\2";
-static const unsigned char CMD_ACK[]   = "A";
-static const unsigned char CMD_READ[]  = "Raan";
-static const unsigned char CMD_WRITE[] = "Waan...";
-static const unsigned char CMD_ENDR[]  = "ENDR";
-static const unsigned char CMD_ENDW[]  = "ENDW";
-static const unsigned char CMD_CWB0[]  = "CWB\4\0\0\0\0";
-static const unsigned char CMD_CWB1[]  = "CWB\4\0\1\0\0";
-
 static volatile IOHIDDeviceRef dev;         // device handle
 static unsigned char transfer_buf[42];      // device buffer
 static unsigned char receive_buf[42];       // receive buffer
 static volatile int nbytes_received = 0;    // receive result
-static unsigned offset = 0;                 // CWD offset
 
 //
 // Send a request to the device.
@@ -57,6 +46,7 @@ void hid_send_recv(const unsigned char *data, unsigned nbytes, unsigned char *rd
 {
     unsigned char buf[42];
     unsigned k;
+    IOReturn result;
 
     memset(buf, 0, sizeof(buf));
     buf[0] = 1;
@@ -80,7 +70,7 @@ void hid_send_recv(const unsigned char *data, unsigned nbytes, unsigned char *rd
     memset(receive_buf, 0, sizeof(receive_buf));
 again:
     // Write to HID device.
-    IOReturn result = IOHIDDeviceSetReport(dev, kIOHIDReportTypeOutput, 0, buf, sizeof(buf));
+    result = IOHIDDeviceSetReport(dev, kIOHIDReportTypeOutput, 0, buf, sizeof(buf));
     if (result != kIOReturnSuccess) {
         fprintf(stderr, "HID output error: %d!\n", result);
         exit(-1);
@@ -89,9 +79,9 @@ again:
     // Run main application loop until reply received.
     CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0, 0);
     for (k = 0; nbytes_received <= 0; k++) {
-        usleep(10000);
+        usleep(100);
         CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0, 0);
-        if (k >= 10) {
+        if (k >= 1000) {
             if (trace_flag > 0) {
                 fprintf(stderr, "No response from HID device!\n");
             }
@@ -179,7 +169,7 @@ static void callback_close(void *ontext,
 //
 // Launch the IOHIDManager.
 //
-const char *hid_init(int vid, int pid)
+int hid_init(int vid, int pid)
 {
     // Create the USB HID Manager.
     IOHIDManagerRef HIDManager = IOHIDManagerCreate(kCFAllocatorDefault,
@@ -210,7 +200,7 @@ const char *hid_init(int vid, int pid)
         if (trace_flag) {
             fprintf(stderr, "Cannot find USB device %04x:%04x\n", vid, pid);
         }
-        return 0;
+        return -1;
     }
 
     // Run main application loop until device found.
@@ -218,44 +208,16 @@ const char *hid_init(int vid, int pid)
     for (k=0; ; k++) {
         CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0, 0);
         if (dev)
-            break;
+            return 0;
+
         if (k >= 3) {
             if (trace_flag) {
                 fprintf(stderr, "Cannot find USB device %04x:%04x\n", vid, pid);
             }
-            return 0;
+            return -1;
         }
         usleep(10000);
     }
-
-    static unsigned char reply[38];
-    unsigned char ack;
-
-    hid_send_recv(CMD_PRG, 7, &ack, 1);
-    if (ack != CMD_ACK[0]) {
-        fprintf(stderr, "%s: Wrong PRD acknowledge %#x, expected %#x\n",
-            __func__, ack, CMD_ACK[0]);
-        return 0;
-    }
-
-    hid_send_recv(CMD_PRG2, 2, reply, 16);
-
-    hid_send_recv(CMD_ACK, 1, &ack, 1);
-    if (ack != CMD_ACK[0]) {
-        fprintf(stderr, "%s: Wrong PRG2 acknowledge %#x, expected %#x\n",
-            __func__, ack, CMD_ACK[0]);
-        return 0;
-    }
-
-    // Reply:
-    // 42 46 2d 35 52 ff ff ff 56 32 31 30 00 04 80 04
-    //  B  F  -  5  R           V  2  1  0
-
-    // Terminate the string.
-    char *p = memchr(reply, 0xff, sizeof(reply));
-    if (p)
-        *p = 0;
-    return (char*)reply;
 }
 
 //
@@ -269,98 +231,3 @@ void hid_close()
     IOHIDDeviceClose(dev, kIOHIDOptionsTypeNone);
     dev = 0;
 }
-
-void hid_read_block(int bno, uint8_t *data, int nbytes)
-{
-    unsigned addr = bno * nbytes;
-    unsigned char ack, cmd[4], reply[32+4];
-    int n;
-
-    if (addr < 0x10000 && offset != 0) {
-        offset = 0;
-        hid_send_recv(CMD_CWB0, 8, &ack, 1);
-        if (ack != CMD_ACK[0]) {
-            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-                __func__, ack, CMD_ACK[0]);
-            exit(-1);
-        }
-    } else if (addr >= 0x10000 && offset == 0) {
-        offset = 0x00010000;
-        hid_send_recv(CMD_CWB1, 8, &ack, 1);
-        if (ack != CMD_ACK[0]) {
-            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-                __func__, ack, CMD_ACK[0]);
-            exit(-1);
-        }
-    }
-
-    for (n=0; n<nbytes; n+=32) {
-        cmd[0] = CMD_READ[0];
-        cmd[1] = (addr + n) >> 8;
-        cmd[2] = addr + n;
-        cmd[3] = 32;
-        hid_send_recv(cmd, 4, reply, sizeof(reply));
-        memcpy(data + n, reply + 4, 32);
-    }
-}
-
-void hid_write_block(int bno, uint8_t *data, int nbytes)
-{
-    unsigned addr = bno * nbytes;
-    unsigned char ack, cmd[4+32];
-    int n;
-
-    if (addr < 0x10000 && offset != 0) {
-        offset = 0;
-        hid_send_recv(CMD_CWB0, 8, &ack, 1);
-        if (ack != CMD_ACK[0]) {
-            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-                __func__, ack, CMD_ACK[0]);
-            exit(-1);
-        }
-    } else if (addr >= 0x10000 && offset == 0) {
-        offset = 0x00010000;
-        hid_send_recv(CMD_CWB1, 8, &ack, 1);
-        if (ack != CMD_ACK[0]) {
-            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-                __func__, ack, CMD_ACK[0]);
-            exit(-1);
-        }
-    }
-
-    for (n=0; n<nbytes; n+=32) {
-        cmd[0] = CMD_WRITE[0];
-        cmd[1] = (addr + n) >> 8;
-        cmd[2] = addr + n;
-        cmd[3] = 32;
-        memcpy(cmd + 4, data + n, 32);
-        hid_send_recv(cmd, 4+32, &ack, 1);
-        if (ack != CMD_ACK[0]) {
-            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-                __func__, ack, CMD_ACK[0]);
-            exit(-1);
-        }
-    }
-}
-
-void hid_read_finish()
-{
-    unsigned char ack;
-
-    hid_send_recv(CMD_ENDR, 4, &ack, 1);
-    if (ack != CMD_ACK[0]) {
-        fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-            __func__, ack, CMD_ACK[0]);
-    }
-}
-
-void hid_write_finish()
-{
-    unsigned char ack;
-
-    hid_send_recv(CMD_ENDW, 4, &ack, 1);
-    if (ack != CMD_ACK[0]) {
-        fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-            __func__, ack, CMD_ACK[0]);
-    }
-}
diff --git a/hid-windows.c b/hid-windows.c
index 17b719a..88c4ea2 100644
--- a/hid-windows.c
+++ b/hid-windows.c
@@ -35,19 +35,8 @@
 #include <stdint.h>
 #include "util.h"
 
-static const unsigned char CMD_PRG[]   = "\2PROGRA";
-static const unsigned char CMD_PRG2[]  = "M\2";
-static const unsigned char CMD_ACK[]   = "A";
-static const unsigned char CMD_READ[]  = "Raan";
-static const unsigned char CMD_WRITE[] = "Waan...";
-static const unsigned char CMD_ENDR[]  = "ENDR";
-static const unsigned char CMD_ENDW[]  = "ENDW";
-static const unsigned char CMD_CWB0[]  = "CWB\4\0\0\0\0";
-static const unsigned char CMD_CWB1[]  = "CWB\4\0\1\0\0";
-
 HANDLE dev = INVALID_HANDLE_VALUE;;         // HID device
 static unsigned char receive_buf[42];       // receive buffer
-static unsigned offset = 0;                 // CWD offset
 
 //
 // Send a request to the device.
@@ -120,24 +109,25 @@ void hid_send_recv(const unsigned char *data, unsigned nbytes, unsigned char *rd
 }
 
 //
+// Open the radio in programming mode.
 // Find a HID device with given GUID, vendor ID and product ID.
-// Return an opened file descriptor.
+// Setup `dev' file descriptor.
 //
-HANDLE find_hid_device(int vid, int pid)
+int hid_init(int vid, int pid)
 {
     static GUID guid = { 0x4d1e55b2, 0xf16f, 0x11cf, { 0x88, 0xcb, 0x00, 0x11, 0x11, 0x00, 0x00, 0x30 } };
-    HANDLE h = INVALID_HANDLE_VALUE;
 
     HDEVINFO devinfo = SetupDiGetClassDevs(&guid, NULL, NULL, DIGCF_PRESENT | DIGCF_INTERFACEDEVICE);
     if (devinfo == INVALID_HANDLE_VALUE) {
         printf("Cannot get devinfo!\n");
-        return 0;
+        return -1;
     }
 
     // Loop through available devices with a given GUID.
     int index;
     SP_INTERFACE_DEVICE_DATA iface;
     iface.cbSize = sizeof(iface);
+    dev = INVALID_HANDLE_VALUE;
     for (index=0; SetupDiEnumDeviceInterfaces(devinfo, NULL, &guid, index, &iface); ++index) {
 
         // Obtain a required size of device detail structure.
@@ -156,22 +146,22 @@ HANDLE find_hid_device(int vid, int pid)
         }
         //printf("Device %d: path %s\n", index, detail->DevicePath);
 
-        h = CreateFile(detail->DevicePath, GENERIC_WRITE | GENERIC_READ,
+        dev = CreateFile(detail->DevicePath, GENERIC_WRITE | GENERIC_READ,
             0, NULL, OPEN_EXISTING, 0, NULL);
-        if (h == INVALID_HANDLE_VALUE) {
+        if (dev == INVALID_HANDLE_VALUE) {
             continue;
         }
 
         // Get the Vendor ID and Product ID for this device.
         HIDD_ATTRIBUTES attrib;
         attrib.Size = sizeof(HIDD_ATTRIBUTES);
-        HidD_GetAttributes(h, &attrib);
+        HidD_GetAttributes(dev, &attrib);
         //printf("Vendor/Product: %04x %04x\n", attrib.VendorID, attrib.ProductID);
 
         // Check the VID/PID.
         if (attrib.VendorID != vid || attrib.ProductID != pid) {
-            CloseHandle(h);
-            h = INVALID_HANDLE_VALUE;
+            CloseHandle(dev);
+            dev = INVALID_HANDLE_VALUE;
             continue;
         }
 
@@ -179,51 +169,14 @@ HANDLE find_hid_device(int vid, int pid)
         break;
     }
     SetupDiDestroyDeviceInfoList(devinfo);
-    return h;
-}
 
-//
-// Open the radio in programming mode.
-//
-const char *hid_init(int vid, int pid)
-{
-    // Find HID device.
-    dev = find_hid_device(vid, pid);
     if (dev == INVALID_HANDLE_VALUE) {
         if (trace_flag) {
             fprintf(stderr, "Cannot find HID device %04x:%04x\n", vid, pid);
         }
-        return 0;
+        return -1;
     }
-
-    static unsigned char reply[38];
-    unsigned char ack;
-
-    hid_send_recv(CMD_PRG, 7, &ack, 1);
-    if (ack != CMD_ACK[0]) {
-        fprintf(stderr, "%s: Wrong PRD acknowledge %#x, expected %#x\n",
-            __func__, ack, CMD_ACK[0]);
-        return 0;
-    }
-
-    hid_send_recv(CMD_PRG2, 2, reply, 16);
-
-    hid_send_recv(CMD_ACK, 1, &ack, 1);
-    if (ack != CMD_ACK[0]) {
-        fprintf(stderr, "%s: Wrong PRG2 acknowledge %#x, expected %#x\n",
-            __func__, ack, CMD_ACK[0]);
-        return 0;
-    }
-
-    // Reply:
-    // 42 46 2d 35 52 ff ff ff 56 32 31 30 00 04 80 04
-    //  B  F  -  5  R           V  2  1  0
-
-    // Terminate the string.
-    char *p = memchr(reply, 0xff, sizeof(reply));
-    if (p)
-        *p = 0;
-    return (char*)reply;
+    return 0;
 }
 
 //
@@ -236,98 +189,3 @@ void hid_close()
         dev = INVALID_HANDLE_VALUE;
     }
 }
-
-void hid_read_block(int bno, uint8_t *data, int nbytes)
-{
-    unsigned addr = bno * nbytes;
-    unsigned char ack, cmd[4], reply[32+4];
-    int n;
-
-    if (addr < 0x10000 && offset != 0) {
-        offset = 0;
-        hid_send_recv(CMD_CWB0, 8, &ack, 1);
-        if (ack != CMD_ACK[0]) {
-            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-                __func__, ack, CMD_ACK[0]);
-            exit(-1);
-        }
-    } else if (addr >= 0x10000 && offset == 0) {
-        offset = 0x00010000;
-        hid_send_recv(CMD_CWB1, 8, &ack, 1);
-        if (ack != CMD_ACK[0]) {
-            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-                __func__, ack, CMD_ACK[0]);
-            exit(-1);
-        }
-    }
-
-    for (n=0; n<nbytes; n+=32) {
-        cmd[0] = CMD_READ[0];
-        cmd[1] = (addr + n) >> 8;
-        cmd[2] = addr + n;
-        cmd[3] = 32;
-        hid_send_recv(cmd, 4, reply, sizeof(reply));
-        memcpy(data + n, reply + 4, 32);
-    }
-}
-
-void hid_write_block(int bno, uint8_t *data, int nbytes)
-{
-    unsigned addr = bno * nbytes;
-    unsigned char ack, cmd[4+32];
-    int n;
-
-    if (addr < 0x10000 && offset != 0) {
-        offset = 0;
-        hid_send_recv(CMD_CWB0, 8, &ack, 1);
-        if (ack != CMD_ACK[0]) {
-            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-                __func__, ack, CMD_ACK[0]);
-            exit(-1);
-        }
-    } else if (addr >= 0x10000 && offset == 0) {
-        offset = 0x00010000;
-        hid_send_recv(CMD_CWB1, 8, &ack, 1);
-        if (ack != CMD_ACK[0]) {
-            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-                __func__, ack, CMD_ACK[0]);
-            exit(-1);
-        }
-    }
-
-    for (n=0; n<nbytes; n+=32) {
-        cmd[0] = CMD_WRITE[0];
-        cmd[1] = (addr + n) >> 8;
-        cmd[2] = addr + n;
-        cmd[3] = 32;
-        memcpy(cmd + 4, data + n, 32);
-        hid_send_recv(cmd, 4+32, &ack, 1);
-        if (ack != CMD_ACK[0]) {
-            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-                __func__, ack, CMD_ACK[0]);
-            exit(-1);
-        }
-    }
-}
-
-void hid_read_finish()
-{
-    unsigned char ack;
-
-    hid_send_recv(CMD_ENDR, 4, &ack, 1);
-    if (ack != CMD_ACK[0]) {
-        fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-            __func__, ack, CMD_ACK[0]);
-    }
-}
-
-void hid_write_finish()
-{
-    unsigned char ack;
-
-    hid_send_recv(CMD_ENDW, 4, &ack, 1);
-    if (ack != CMD_ACK[0]) {
-        fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
-            __func__, ack, CMD_ACK[0]);
-    }
-}
diff --git a/hid.c b/hid.c
new file mode 100644
index 0000000..26e6f07
--- /dev/null
+++ b/hid.c
@@ -0,0 +1,174 @@
+/*
+ * HID routines, OS independent.
+ *
+ * Copyright (C) 2018 Serge Vakulenko, KK6ABQ
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   1. Redistributions of source code must retain the above copyright notice,
+ *      this list of conditions and the following disclaimer.
+ *   2. Redistributions in binary form must reproduce the above copyright
+ *      notice, this list of conditions and the following disclaimer in the
+ *      documentation and/or other materials provided with the distribution.
+ *   3. The name of the author may not be used to endorse or promote products
+ *      derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
+ * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
+ * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+ * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include "util.h"
+
+static const unsigned char CMD_PRG[]   = "\2PROGRA";
+static const unsigned char CMD_PRG2[]  = "M\2";
+static const unsigned char CMD_ACK[]   = "A";
+static const unsigned char CMD_READ[]  = "Raan";
+static const unsigned char CMD_WRITE[] = "Waan...";
+static const unsigned char CMD_ENDR[]  = "ENDR";
+static const unsigned char CMD_ENDW[]  = "ENDW";
+static const unsigned char CMD_CWB0[]  = "CWB\4\0\0\0\0";
+static const unsigned char CMD_CWB1[]  = "CWB\4\0\1\0\0";
+
+static unsigned offset = 0;                 // CWD offset
+
+//
+// Query and return the device identification string.
+//
+const char *hid_identify()
+{
+    static unsigned char reply[38];
+    unsigned char ack;
+
+    hid_send_recv(CMD_PRG, 7, &ack, 1);
+    if (ack != CMD_ACK[0]) {
+        fprintf(stderr, "%s: Wrong PRD acknowledge %#x, expected %#x\n",
+            __func__, ack, CMD_ACK[0]);
+        return 0;
+    }
+
+    hid_send_recv(CMD_PRG2, 2, reply, 16);
+
+    hid_send_recv(CMD_ACK, 1, &ack, 1);
+    if (ack != CMD_ACK[0]) {
+        fprintf(stderr, "%s: Wrong PRG2 acknowledge %#x, expected %#x\n",
+            __func__, ack, CMD_ACK[0]);
+        return 0;
+    }
+
+    // Reply:
+    // 42 46 2d 35 52 ff ff ff 56 32 31 30 00 04 80 04
+    //  B  F  -  5  R           V  2  1  0
+
+    // Terminate the string.
+    char *p = memchr(reply, 0xff, sizeof(reply));
+    if (p)
+        *p = 0;
+    return (char*)reply;
+}
+
+void hid_read_block(int bno, unsigned char *data, int nbytes)
+{
+    unsigned addr = bno * nbytes;
+    unsigned char ack, cmd[4], reply[32+4];
+    int n;
+
+    if (addr < 0x10000 && offset != 0) {
+        offset = 0;
+        hid_send_recv(CMD_CWB0, 8, &ack, 1);
+        if (ack != CMD_ACK[0]) {
+            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
+                __func__, ack, CMD_ACK[0]);
+            exit(-1);
+        }
+    } else if (addr >= 0x10000 && offset == 0) {
+        offset = 0x00010000;
+        hid_send_recv(CMD_CWB1, 8, &ack, 1);
+        if (ack != CMD_ACK[0]) {
+            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
+                __func__, ack, CMD_ACK[0]);
+            exit(-1);
+        }
+    }
+
+    for (n=0; n<nbytes; n+=32) {
+        cmd[0] = CMD_READ[0];
+        cmd[1] = (addr + n) >> 8;
+        cmd[2] = addr + n;
+        cmd[3] = 32;
+        hid_send_recv(cmd, 4, reply, sizeof(reply));
+        memcpy(data + n, reply + 4, 32);
+    }
+}
+
+void hid_write_block(int bno, unsigned char *data, int nbytes)
+{
+    unsigned addr = bno * nbytes;
+    unsigned char ack, cmd[4+32];
+    int n;
+
+    if (addr < 0x10000 && offset != 0) {
+        offset = 0;
+        hid_send_recv(CMD_CWB0, 8, &ack, 1);
+        if (ack != CMD_ACK[0]) {
+            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
+                __func__, ack, CMD_ACK[0]);
+            exit(-1);
+        }
+    } else if (addr >= 0x10000 && offset == 0) {
+        offset = 0x00010000;
+        hid_send_recv(CMD_CWB1, 8, &ack, 1);
+        if (ack != CMD_ACK[0]) {
+            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
+                __func__, ack, CMD_ACK[0]);
+            exit(-1);
+        }
+    }
+
+    for (n=0; n<nbytes; n+=32) {
+        cmd[0] = CMD_WRITE[0];
+        cmd[1] = (addr + n) >> 8;
+        cmd[2] = addr + n;
+        cmd[3] = 32;
+        memcpy(cmd + 4, data + n, 32);
+        hid_send_recv(cmd, 4+32, &ack, 1);
+        if (ack != CMD_ACK[0]) {
+            fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
+                __func__, ack, CMD_ACK[0]);
+            exit(-1);
+        }
+    }
+}
+
+void hid_read_finish()
+{
+    unsigned char ack;
+
+    hid_send_recv(CMD_ENDR, 4, &ack, 1);
+    if (ack != CMD_ACK[0]) {
+        fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
+            __func__, ack, CMD_ACK[0]);
+    }
+}
+
+void hid_write_finish()
+{
+    unsigned char ack;
+
+    hid_send_recv(CMD_ENDW, 4, &ack, 1);
+    if (ack != CMD_ACK[0]) {
+        fprintf(stderr, "%s: Wrong acknowledge %#x, expected %#x\n",
+            __func__, ack, CMD_ACK[0]);
+    }
+}
diff --git a/radio.c b/radio.c
index d613c90..c204503 100644
--- a/radio.c
+++ b/radio.c
@@ -91,7 +91,8 @@ void radio_connect()
     ident = dfu_init(0x0483, 0xdf11);
     if (! ident) {
         // Try RD-5R.
-        ident = hid_init(0x15a2, 0x0073);
+        if (hid_init(0x15a2, 0x0073) >= 0)
+            ident = hid_identify();
     }
     if (! ident) {
         fprintf(stderr, "No radio detected.\n");
diff --git a/util.h b/util.h
index c4bf349..99ce826 100644
--- a/util.h
+++ b/util.h
@@ -68,9 +68,10 @@ void dfu_reboot(void);
 //
 // HID functions.
 //
-const char *hid_init(int vid, int pid);
+int hid_init(int vid, int pid);
+const char *hid_identify(void);
 void hid_close(void);
-int hid_write_read(const unsigned char *data, unsigned length, unsigned char *reply, unsigned rlength);
+void hid_send_recv(const unsigned char *data, unsigned nbytes, unsigned char *rdata, unsigned rlength);
 void hid_read_block(int bno, unsigned char *data, int nbytes);
 void hid_read_finish(void);
 void hid_write_block(int bno, unsigned char *data, int nbytes);