mbed-os

Fork of mbed-os by erkin yucel

Committer:
elessair
Date:
Sun Oct 23 15:10:02 2016 +0000
Revision:
0:f269e3021894
Initial commit

Who changed what in which revision?

UserRevisionLine numberNew contents of line
elessair 0:f269e3021894 1 /* mbed USBHost Library
elessair 0:f269e3021894 2 * Copyright (c) 2006-2013 ARM Limited
elessair 0:f269e3021894 3 *
elessair 0:f269e3021894 4 * Licensed under the Apache License, Version 2.0 (the "License");
elessair 0:f269e3021894 5 * you may not use this file except in compliance with the License.
elessair 0:f269e3021894 6 * You may obtain a copy of the License at
elessair 0:f269e3021894 7 *
elessair 0:f269e3021894 8 * http://www.apache.org/licenses/LICENSE-2.0
elessair 0:f269e3021894 9 *
elessair 0:f269e3021894 10 * Unless required by applicable law or agreed to in writing, software
elessair 0:f269e3021894 11 * distributed under the License is distributed on an "AS IS" BASIS,
elessair 0:f269e3021894 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
elessair 0:f269e3021894 13 * See the License for the specific language governing permissions and
elessair 0:f269e3021894 14 * limitations under the License.
elessair 0:f269e3021894 15 */
elessair 0:f269e3021894 16
elessair 0:f269e3021894 17 #include "USBHostMSD.h"
elessair 0:f269e3021894 18
elessair 0:f269e3021894 19 #if USBHOST_MSD
elessair 0:f269e3021894 20
elessair 0:f269e3021894 21 #include "dbg.h"
elessair 0:f269e3021894 22
elessair 0:f269e3021894 23 #define CBW_SIGNATURE 0x43425355
elessair 0:f269e3021894 24 #define CSW_SIGNATURE 0x53425355
elessair 0:f269e3021894 25
elessair 0:f269e3021894 26 #define DEVICE_TO_HOST 0x80
elessair 0:f269e3021894 27 #define HOST_TO_DEVICE 0x00
elessair 0:f269e3021894 28
elessair 0:f269e3021894 29 #define GET_MAX_LUN (0xFE)
elessair 0:f269e3021894 30 #define BO_MASS_STORAGE_RESET (0xFF)
elessair 0:f269e3021894 31
elessair 0:f269e3021894 32 USBHostMSD::USBHostMSD(const char * rootdir) : FATFileSystem(rootdir)
elessair 0:f269e3021894 33 {
elessair 0:f269e3021894 34 host = USBHost::getHostInst();
elessair 0:f269e3021894 35 init();
elessair 0:f269e3021894 36 }
elessair 0:f269e3021894 37
elessair 0:f269e3021894 38 void USBHostMSD::init() {
elessair 0:f269e3021894 39 dev_connected = false;
elessair 0:f269e3021894 40 dev = NULL;
elessair 0:f269e3021894 41 bulk_in = NULL;
elessair 0:f269e3021894 42 bulk_out = NULL;
elessair 0:f269e3021894 43 dev_connected = false;
elessair 0:f269e3021894 44 blockSize = 0;
elessair 0:f269e3021894 45 blockCount = 0;
elessair 0:f269e3021894 46 msd_intf = -1;
elessair 0:f269e3021894 47 msd_device_found = false;
elessair 0:f269e3021894 48 disk_init = false;
elessair 0:f269e3021894 49 dev_connected = false;
elessair 0:f269e3021894 50 nb_ep = 0;
elessair 0:f269e3021894 51 }
elessair 0:f269e3021894 52
elessair 0:f269e3021894 53
elessair 0:f269e3021894 54 bool USBHostMSD::connected()
elessair 0:f269e3021894 55 {
elessair 0:f269e3021894 56 return dev_connected;
elessair 0:f269e3021894 57 }
elessair 0:f269e3021894 58
elessair 0:f269e3021894 59 bool USBHostMSD::connect()
elessair 0:f269e3021894 60 {
elessair 0:f269e3021894 61
elessair 0:f269e3021894 62 if (dev_connected) {
elessair 0:f269e3021894 63 return true;
elessair 0:f269e3021894 64 }
elessair 0:f269e3021894 65
elessair 0:f269e3021894 66 for (uint8_t i = 0; i < MAX_DEVICE_CONNECTED; i++) {
elessair 0:f269e3021894 67 if ((dev = host->getDevice(i)) != NULL) {
elessair 0:f269e3021894 68
elessair 0:f269e3021894 69 USB_DBG("Trying to connect MSD device\r\n");
elessair 0:f269e3021894 70
elessair 0:f269e3021894 71 if(host->enumerate(dev, this))
elessair 0:f269e3021894 72 break;
elessair 0:f269e3021894 73
elessair 0:f269e3021894 74 if (msd_device_found) {
elessair 0:f269e3021894 75 bulk_in = dev->getEndpoint(msd_intf, BULK_ENDPOINT, IN);
elessair 0:f269e3021894 76 bulk_out = dev->getEndpoint(msd_intf, BULK_ENDPOINT, OUT);
elessair 0:f269e3021894 77
elessair 0:f269e3021894 78 if (!bulk_in || !bulk_out)
elessair 0:f269e3021894 79 continue;
elessair 0:f269e3021894 80
elessair 0:f269e3021894 81 USB_INFO("New MSD device: VID:%04x PID:%04x [dev: %p - intf: %d]", dev->getVid(), dev->getPid(), dev, msd_intf);
elessair 0:f269e3021894 82 dev->setName("MSD", msd_intf);
elessair 0:f269e3021894 83 host->registerDriver(dev, msd_intf, this, &USBHostMSD::init);
elessair 0:f269e3021894 84
elessair 0:f269e3021894 85 dev_connected = true;
elessair 0:f269e3021894 86 return true;
elessair 0:f269e3021894 87 }
elessair 0:f269e3021894 88 } //if()
elessair 0:f269e3021894 89 } //for()
elessair 0:f269e3021894 90 init();
elessair 0:f269e3021894 91 return false;
elessair 0:f269e3021894 92 }
elessair 0:f269e3021894 93
elessair 0:f269e3021894 94 /*virtual*/ void USBHostMSD::setVidPid(uint16_t vid, uint16_t pid)
elessair 0:f269e3021894 95 {
elessair 0:f269e3021894 96 // we don't check VID/PID for MSD driver
elessair 0:f269e3021894 97 }
elessair 0:f269e3021894 98
elessair 0:f269e3021894 99 /*virtual*/ bool USBHostMSD::parseInterface(uint8_t intf_nb, uint8_t intf_class, uint8_t intf_subclass, uint8_t intf_protocol) //Must return true if the interface should be parsed
elessair 0:f269e3021894 100 {
elessair 0:f269e3021894 101 if ((msd_intf == -1) &&
elessair 0:f269e3021894 102 (intf_class == MSD_CLASS) &&
elessair 0:f269e3021894 103 (intf_subclass == 0x06) &&
elessair 0:f269e3021894 104 (intf_protocol == 0x50)) {
elessair 0:f269e3021894 105 msd_intf = intf_nb;
elessair 0:f269e3021894 106 return true;
elessair 0:f269e3021894 107 }
elessair 0:f269e3021894 108 return false;
elessair 0:f269e3021894 109 }
elessair 0:f269e3021894 110
elessair 0:f269e3021894 111 /*virtual*/ bool USBHostMSD::useEndpoint(uint8_t intf_nb, ENDPOINT_TYPE type, ENDPOINT_DIRECTION dir) //Must return true if the endpoint will be used
elessair 0:f269e3021894 112 {
elessair 0:f269e3021894 113 if (intf_nb == msd_intf) {
elessair 0:f269e3021894 114 if (type == BULK_ENDPOINT) {
elessair 0:f269e3021894 115 nb_ep++;
elessair 0:f269e3021894 116 if (nb_ep == 2)
elessair 0:f269e3021894 117 msd_device_found = true;
elessair 0:f269e3021894 118 return true;
elessair 0:f269e3021894 119 }
elessair 0:f269e3021894 120 }
elessair 0:f269e3021894 121 return false;
elessair 0:f269e3021894 122 }
elessair 0:f269e3021894 123
elessair 0:f269e3021894 124
elessair 0:f269e3021894 125 int USBHostMSD::testUnitReady() {
elessair 0:f269e3021894 126 USB_DBG("Test unit ready");
elessair 0:f269e3021894 127 return SCSITransfer(NULL, 6, DEVICE_TO_HOST, 0, 0);
elessair 0:f269e3021894 128 }
elessair 0:f269e3021894 129
elessair 0:f269e3021894 130
elessair 0:f269e3021894 131 int USBHostMSD::readCapacity() {
elessair 0:f269e3021894 132 USB_DBG("Read capacity");
elessair 0:f269e3021894 133 uint8_t cmd[10] = {0x25,0,0,0,0,0,0,0,0,0};
elessair 0:f269e3021894 134 uint8_t result[8];
elessair 0:f269e3021894 135 int status = SCSITransfer(cmd, 10, DEVICE_TO_HOST, result, 8);
elessair 0:f269e3021894 136 if (status == 0) {
elessair 0:f269e3021894 137 blockCount = (result[0] << 24) | (result[1] << 16) | (result[2] << 8) | result[3];
elessair 0:f269e3021894 138 blockSize = (result[4] << 24) | (result[5] << 16) | (result[6] << 8) | result[7];
elessair 0:f269e3021894 139 USB_INFO("MSD [dev: %p] - blockCount: %u, blockSize: %d, Capacity: %d\r\n", dev, blockCount, blockSize, blockCount*blockSize);
elessair 0:f269e3021894 140 }
elessair 0:f269e3021894 141 return status;
elessair 0:f269e3021894 142 }
elessair 0:f269e3021894 143
elessair 0:f269e3021894 144
elessair 0:f269e3021894 145 int USBHostMSD::SCSIRequestSense() {
elessair 0:f269e3021894 146 USB_DBG("Request sense");
elessair 0:f269e3021894 147 uint8_t cmd[6] = {0x03,0,0,0,18,0};
elessair 0:f269e3021894 148 uint8_t result[18];
elessair 0:f269e3021894 149 int status = SCSITransfer(cmd, 6, DEVICE_TO_HOST, result, 18);
elessair 0:f269e3021894 150 return status;
elessair 0:f269e3021894 151 }
elessair 0:f269e3021894 152
elessair 0:f269e3021894 153
elessair 0:f269e3021894 154 int USBHostMSD::inquiry(uint8_t lun, uint8_t page_code) {
elessair 0:f269e3021894 155 USB_DBG("Inquiry");
elessair 0:f269e3021894 156 uint8_t evpd = (page_code == 0) ? 0 : 1;
elessair 0:f269e3021894 157 uint8_t cmd[6] = {0x12, uint8_t((lun << 5) | evpd), page_code, 0, 36, 0};
elessair 0:f269e3021894 158 uint8_t result[36];
elessair 0:f269e3021894 159 int status = SCSITransfer(cmd, 6, DEVICE_TO_HOST, result, 36);
elessair 0:f269e3021894 160 if (status == 0) {
elessair 0:f269e3021894 161 char vid_pid[17];
elessair 0:f269e3021894 162 memcpy(vid_pid, &result[8], 8);
elessair 0:f269e3021894 163 vid_pid[8] = 0;
elessair 0:f269e3021894 164 USB_INFO("MSD [dev: %p] - Vendor ID: %s", dev, vid_pid);
elessair 0:f269e3021894 165
elessair 0:f269e3021894 166 memcpy(vid_pid, &result[16], 16);
elessair 0:f269e3021894 167 vid_pid[16] = 0;
elessair 0:f269e3021894 168 USB_INFO("MSD [dev: %p] - Product ID: %s", dev, vid_pid);
elessair 0:f269e3021894 169
elessair 0:f269e3021894 170 memcpy(vid_pid, &result[32], 4);
elessair 0:f269e3021894 171 vid_pid[4] = 0;
elessair 0:f269e3021894 172 USB_INFO("MSD [dev: %p] - Product rev: %s", dev, vid_pid);
elessair 0:f269e3021894 173 }
elessair 0:f269e3021894 174 return status;
elessair 0:f269e3021894 175 }
elessair 0:f269e3021894 176
elessair 0:f269e3021894 177 int USBHostMSD::checkResult(uint8_t res, USBEndpoint * ep) {
elessair 0:f269e3021894 178 // if ep stalled: send clear feature
elessair 0:f269e3021894 179 if (res == USB_TYPE_STALL_ERROR) {
elessair 0:f269e3021894 180 res = host->controlWrite( dev,
elessair 0:f269e3021894 181 USB_RECIPIENT_ENDPOINT | USB_HOST_TO_DEVICE | USB_REQUEST_TYPE_STANDARD,
elessair 0:f269e3021894 182 CLEAR_FEATURE,
elessair 0:f269e3021894 183 0, ep->getAddress(), NULL, 0);
elessair 0:f269e3021894 184 // set state to IDLE if clear feature successful
elessair 0:f269e3021894 185 if (res == USB_TYPE_OK) {
elessair 0:f269e3021894 186 ep->setState(USB_TYPE_IDLE);
elessair 0:f269e3021894 187 }
elessair 0:f269e3021894 188 }
elessair 0:f269e3021894 189
elessair 0:f269e3021894 190 if (res != USB_TYPE_OK)
elessair 0:f269e3021894 191 return -1;
elessair 0:f269e3021894 192
elessair 0:f269e3021894 193 return 0;
elessair 0:f269e3021894 194 }
elessair 0:f269e3021894 195
elessair 0:f269e3021894 196
elessair 0:f269e3021894 197 int USBHostMSD::SCSITransfer(uint8_t * cmd, uint8_t cmd_len, int flags, uint8_t * data, uint32_t transfer_len) {
elessair 0:f269e3021894 198
elessair 0:f269e3021894 199 int res = 0;
elessair 0:f269e3021894 200
elessair 0:f269e3021894 201 cbw.Signature = CBW_SIGNATURE;
elessair 0:f269e3021894 202 cbw.Tag = 0;
elessair 0:f269e3021894 203 cbw.DataLength = transfer_len;
elessair 0:f269e3021894 204 cbw.Flags = flags;
elessair 0:f269e3021894 205 cbw.LUN = 0;
elessair 0:f269e3021894 206 cbw.CBLength = cmd_len;
elessair 0:f269e3021894 207 memset(cbw.CB,0,sizeof(cbw.CB));
elessair 0:f269e3021894 208 if (cmd) {
elessair 0:f269e3021894 209 memcpy(cbw.CB,cmd,cmd_len);
elessair 0:f269e3021894 210 }
elessair 0:f269e3021894 211
elessair 0:f269e3021894 212 // send the cbw
elessair 0:f269e3021894 213 USB_DBG("Send CBW");
elessair 0:f269e3021894 214 res = host->bulkWrite(dev, bulk_out,(uint8_t *)&cbw, 31);
elessair 0:f269e3021894 215 if (checkResult(res, bulk_out))
elessair 0:f269e3021894 216 return -1;
elessair 0:f269e3021894 217
elessair 0:f269e3021894 218 // data stage if needed
elessair 0:f269e3021894 219 if (data) {
elessair 0:f269e3021894 220 USB_DBG("data stage");
elessair 0:f269e3021894 221 if (flags == HOST_TO_DEVICE) {
elessair 0:f269e3021894 222
elessair 0:f269e3021894 223 res = host->bulkWrite(dev, bulk_out, data, transfer_len);
elessair 0:f269e3021894 224 if (checkResult(res, bulk_out))
elessair 0:f269e3021894 225 return -1;
elessair 0:f269e3021894 226
elessair 0:f269e3021894 227 } else if (flags == DEVICE_TO_HOST) {
elessair 0:f269e3021894 228
elessair 0:f269e3021894 229 res = host->bulkRead(dev, bulk_in, data, transfer_len);
elessair 0:f269e3021894 230 if (checkResult(res, bulk_in))
elessair 0:f269e3021894 231 return -1;
elessair 0:f269e3021894 232 }
elessair 0:f269e3021894 233 }
elessair 0:f269e3021894 234
elessair 0:f269e3021894 235 // status stage
elessair 0:f269e3021894 236 csw.Signature = 0;
elessair 0:f269e3021894 237 USB_DBG("Read CSW");
elessair 0:f269e3021894 238 res = host->bulkRead(dev, bulk_in,(uint8_t *)&csw, 13);
elessair 0:f269e3021894 239 if (checkResult(res, bulk_in))
elessair 0:f269e3021894 240 return -1;
elessair 0:f269e3021894 241
elessair 0:f269e3021894 242 if (csw.Signature != CSW_SIGNATURE) {
elessair 0:f269e3021894 243 return -1;
elessair 0:f269e3021894 244 }
elessair 0:f269e3021894 245
elessair 0:f269e3021894 246 USB_DBG("recv csw: status: %d", csw.Status);
elessair 0:f269e3021894 247
elessair 0:f269e3021894 248 // ModeSense?
elessair 0:f269e3021894 249 if ((csw.Status == 1) && (cmd[0] != 0x03)) {
elessair 0:f269e3021894 250 USB_DBG("request mode sense");
elessair 0:f269e3021894 251 return SCSIRequestSense();
elessair 0:f269e3021894 252 }
elessair 0:f269e3021894 253
elessair 0:f269e3021894 254 // perform reset recovery
elessair 0:f269e3021894 255 if ((csw.Status == 2) && (cmd[0] != 0x03)) {
elessair 0:f269e3021894 256
elessair 0:f269e3021894 257 // send Bulk-Only Mass Storage Reset request
elessair 0:f269e3021894 258 res = host->controlWrite( dev,
elessair 0:f269e3021894 259 USB_RECIPIENT_INTERFACE | USB_HOST_TO_DEVICE | USB_REQUEST_TYPE_CLASS,
elessair 0:f269e3021894 260 BO_MASS_STORAGE_RESET,
elessair 0:f269e3021894 261 0, msd_intf, NULL, 0);
elessair 0:f269e3021894 262
elessair 0:f269e3021894 263 // unstall both endpoints
elessair 0:f269e3021894 264 res = host->controlWrite( dev,
elessair 0:f269e3021894 265 USB_RECIPIENT_ENDPOINT | USB_HOST_TO_DEVICE | USB_REQUEST_TYPE_STANDARD,
elessair 0:f269e3021894 266 CLEAR_FEATURE,
elessair 0:f269e3021894 267 0, bulk_in->getAddress(), NULL, 0);
elessair 0:f269e3021894 268
elessair 0:f269e3021894 269 res = host->controlWrite( dev,
elessair 0:f269e3021894 270 USB_RECIPIENT_ENDPOINT | USB_HOST_TO_DEVICE | USB_REQUEST_TYPE_STANDARD,
elessair 0:f269e3021894 271 CLEAR_FEATURE,
elessair 0:f269e3021894 272 0, bulk_out->getAddress(), NULL, 0);
elessair 0:f269e3021894 273
elessair 0:f269e3021894 274 }
elessair 0:f269e3021894 275
elessair 0:f269e3021894 276 return csw.Status;
elessair 0:f269e3021894 277 }
elessair 0:f269e3021894 278
elessair 0:f269e3021894 279
elessair 0:f269e3021894 280 int USBHostMSD::dataTransfer(uint8_t * buf, uint32_t block, uint8_t nbBlock, int direction) {
elessair 0:f269e3021894 281 uint8_t cmd[10];
elessair 0:f269e3021894 282 memset(cmd,0,10);
elessair 0:f269e3021894 283 cmd[0] = (direction == DEVICE_TO_HOST) ? 0x28 : 0x2A;
elessair 0:f269e3021894 284
elessair 0:f269e3021894 285 cmd[2] = (block >> 24) & 0xff;
elessair 0:f269e3021894 286 cmd[3] = (block >> 16) & 0xff;
elessair 0:f269e3021894 287 cmd[4] = (block >> 8) & 0xff;
elessair 0:f269e3021894 288 cmd[5] = block & 0xff;
elessair 0:f269e3021894 289
elessair 0:f269e3021894 290 cmd[7] = (nbBlock >> 8) & 0xff;
elessair 0:f269e3021894 291 cmd[8] = nbBlock & 0xff;
elessair 0:f269e3021894 292
elessair 0:f269e3021894 293 return SCSITransfer(cmd, 10, direction, buf, blockSize*nbBlock);
elessair 0:f269e3021894 294 }
elessair 0:f269e3021894 295
elessair 0:f269e3021894 296 int USBHostMSD::getMaxLun() {
elessair 0:f269e3021894 297 uint8_t buf[1], res;
elessair 0:f269e3021894 298 res = host->controlRead( dev, USB_RECIPIENT_INTERFACE | USB_DEVICE_TO_HOST | USB_REQUEST_TYPE_CLASS,
elessair 0:f269e3021894 299 0xfe, 0, msd_intf, buf, 1);
elessair 0:f269e3021894 300 USB_DBG("max lun: %d", buf[0]);
elessair 0:f269e3021894 301 return res;
elessair 0:f269e3021894 302 }
elessair 0:f269e3021894 303
elessair 0:f269e3021894 304 int USBHostMSD::disk_initialize() {
elessair 0:f269e3021894 305 USB_DBG("FILESYSTEM: init");
elessair 0:f269e3021894 306 uint16_t i, timeout = 10;
elessair 0:f269e3021894 307
elessair 0:f269e3021894 308 getMaxLun();
elessair 0:f269e3021894 309
elessair 0:f269e3021894 310 for (i = 0; i < timeout; i++) {
elessair 0:f269e3021894 311 Thread::wait(100);
elessair 0:f269e3021894 312 if (!testUnitReady())
elessair 0:f269e3021894 313 break;
elessair 0:f269e3021894 314 }
elessair 0:f269e3021894 315
elessair 0:f269e3021894 316 if (i == timeout) {
elessair 0:f269e3021894 317 disk_init = false;
elessair 0:f269e3021894 318 return -1;
elessair 0:f269e3021894 319 }
elessair 0:f269e3021894 320
elessair 0:f269e3021894 321 inquiry(0, 0);
elessair 0:f269e3021894 322 disk_init = 1;
elessair 0:f269e3021894 323 return readCapacity();
elessair 0:f269e3021894 324 }
elessair 0:f269e3021894 325
elessair 0:f269e3021894 326 int USBHostMSD::disk_write(const uint8_t* buffer, uint32_t block_number, uint32_t count) {
elessair 0:f269e3021894 327 USB_DBG("FILESYSTEM: write block: %lld, count: %d", block_number, count);
elessair 0:f269e3021894 328 if (!disk_init) {
elessair 0:f269e3021894 329 disk_initialize();
elessair 0:f269e3021894 330 }
elessair 0:f269e3021894 331 if (!disk_init)
elessair 0:f269e3021894 332 return -1;
elessair 0:f269e3021894 333 for (uint32_t b = block_number; b < block_number + count; b++) {
elessair 0:f269e3021894 334 if (dataTransfer((uint8_t*)buffer, b, 1, HOST_TO_DEVICE))
elessair 0:f269e3021894 335 return -1;
elessair 0:f269e3021894 336 buffer += 512;
elessair 0:f269e3021894 337 }
elessair 0:f269e3021894 338 return 0;
elessair 0:f269e3021894 339 }
elessair 0:f269e3021894 340
elessair 0:f269e3021894 341 int USBHostMSD::disk_read(uint8_t* buffer, uint32_t block_number, uint32_t count) {
elessair 0:f269e3021894 342 USB_DBG("FILESYSTEM: read block: %lld, count: %d", block_number, count);
elessair 0:f269e3021894 343 if (!disk_init) {
elessair 0:f269e3021894 344 disk_initialize();
elessair 0:f269e3021894 345 }
elessair 0:f269e3021894 346 if (!disk_init)
elessair 0:f269e3021894 347 return -1;
elessair 0:f269e3021894 348 for (uint32_t b = block_number; b < block_number + count; b++) {
elessair 0:f269e3021894 349 if (dataTransfer((uint8_t*)buffer, b, 1, DEVICE_TO_HOST))
elessair 0:f269e3021894 350 return -1;
elessair 0:f269e3021894 351 buffer += 512;
elessair 0:f269e3021894 352 }
elessair 0:f269e3021894 353 return 0;
elessair 0:f269e3021894 354 }
elessair 0:f269e3021894 355
elessair 0:f269e3021894 356 uint32_t USBHostMSD::disk_sectors() {
elessair 0:f269e3021894 357 USB_DBG("FILESYSTEM: sectors");
elessair 0:f269e3021894 358 if (!disk_init) {
elessair 0:f269e3021894 359 disk_initialize();
elessair 0:f269e3021894 360 }
elessair 0:f269e3021894 361 if (!disk_init)
elessair 0:f269e3021894 362 return 0;
elessair 0:f269e3021894 363 return blockCount;
elessair 0:f269e3021894 364 }
elessair 0:f269e3021894 365
elessair 0:f269e3021894 366 #endif