aboutsummaryrefslogblamecommitdiff
path: root/nuttx/drivers/mtd/sst25.c
blob: adffb7cfcaa6ce80491b079cc28a2cdc8f286498 (plain) (tree)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895






























































































































































































































































































































































































































































































































































































































































































































































































































































































































                                                                                                    
/************************************************************************************
 * drivers/mtd/m25px.c
 * Driver for SPI-based SST25 FLASH.
 *
 *   Copyright (C) 2012 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * 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. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "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
 * COPYRIGHT OWNER OR CONTRIBUTORS 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.
 *
 ************************************************************************************/

/************************************************************************************
 * Included Files
 ************************************************************************************/

#include <nuttx/config.h>

#include <sys/types.h>

#include <stdint.h>
#include <stdbool.h>
#include <stdlib.h>
#include <unistd.h>
#include <assert.h>
#include <errno.h>
#include <debug.h>

#include <nuttx/kmalloc.h>
#include <nuttx/fs/ioctl.h>
#include <nuttx/spi.h>
#include <nuttx/mtd.h>

/************************************************************************************
 * Pre-processor Definitions
 ************************************************************************************/
/* Configuration ********************************************************************/
/* Per the data sheet, MP25P10 parts can be driven with either SPI mode 0 (CPOL=0 and
 * CPHA=0) or mode 3 (CPOL=1 and CPHA=1). But I have heard that other devices can
 * operated in mode 0 or 1.  So you may need to specify CONFIG_SST25_SPIMODE to
 * select the best mode for your device.  If CONFIG_SST25_SPIMODE is not defined,
 * mode 0 will be used.
 */

#ifndef CONFIG_SST25_SPIMODE
#  define CONFIG_SST25_SPIMODE SPIDEV_MODE0
#endif

/* SPI Frequency.  May be up to 25MHz. */

#ifndef CONFIG_SST25_SPIFREQUENCY
#  define CONFIG_SST25_SPIFREQUENCY 20000000
#endif

/* SST25 Instructions ***************************************************************/
/*      Command                    Value      Description               Addr   Data */
/*                                                                         Dummy    */
#define SST25_READ                  0x03    /* Read data bytes           3   0  >=1 */
#define SST25_FAST_READ             0x0b    /* Higher speed read         3   1  >=1 */
#define SST25_SE                    0x20    /* 4Kb Sector erase          3   0   0  */
#define SST25_BE32                  0x52    /* 32Kbit block Erase        3   0   0  */
#define SST25_BE64                  0xd8    /* 64Kbit block Erase        3   0   0  */
#define SST25_CE                    0xc7    /* Chip erase                0   0   0  */
#define SST25_CE_ALT                0x60    /* Chip erase (alternate)    0   0   0  */
#define SST25_BP                    0x02    /* Byte program              3   0   1  */
#define SST25_AAI                   0xad    /* Auto address increment    3   0  >=2 */
#define SST25_RDSR                  0x05    /* Read status register      0   0  >=1 */
#define SST25_EWSR                  0x50    /* Write enable status       0   0   0  */
#define SST25_WRSR                  0x01    /* Write Status Register     0   0   1  */
#define SST25_WREN                  0x06    /* Write Enable              0   0   0  */
#define SST25_WRDI                  0x04    /* Write Disable             0   0   0  */
#define SST25_RDID                  0xab    /* Read Identification       0   0  >=1 */
#define SST25_RDID_ALT              0x90    /* Read Identification (alt) 0   0  >=1 */
#define SST25_JEDEC_ID              0x9f    /* JEDEC ID read             0   0  >=3 */
#define SST25_EBSY                  0x70    /* Enable SO RY/BY# status   0   0   0  */
#define SST25_DBSY                  0x80    /* Disable SO RY/BY# status  0   0   0  */

/* SST25 Registers ******************************************************************/
/* Read ID (RDID) register values */

#define SST25_MANUFACTURER          0xbf  /* SST manufacturer ID */
#define SST25_VF032_DEVID           0x20  /* SSTVF032B device ID */

/* JEDEC Read ID register values */

#define SST25_JEDEC_MANUFACTURER    0xbf  /* SST manufacturer ID */
#define SST25_JEDEC_MEMORY_TYPE     0x25  /* SST25 memory type */
#define SST25_JEDEC_MEMORY_CAPACITY 0x4a  /* SST25VF032B memory capacity */

/* Status register bit definitions */

#define SST25_SR_BUSY               (1 << 0)  /* Bit 0: Write in progress */
#define SST25_SR_WEL                (1 << 1)  /* Bit 1: Write enable latch bit */
#define SST25_SR_BP_SHIFT           (2)       /* Bits 2-5: Block protect bits */
#define SST25_SR_BP_MASK            (15 << SST25_SR_BP_SHIFT)
#  define SST25_SR_BP_NONE          (0 << SST25_SR_BP_SHIFT) /* Unprotected */
#  define SST25_SR_BP_UPPER64th     (1 << SST25_SR_BP_SHIFT) /* Upper 64th */
#  define SST25_SR_BP_UPPER32nd     (2 << SST25_SR_BP_SHIFT) /* Upper 32nd */
#  define SST25_SR_BP_UPPER16th     (3 << SST25_SR_BP_SHIFT) /* Upper 16th */
#  define SST25_SR_BP_UPPER8th      (4 << SST25_SR_BP_SHIFT) /* Upper 8th */
#  define SST25_SR_BP_UPPERQTR      (5 << SST25_SR_BP_SHIFT) /* Upper quarter */
#  define SST25_SR_BP_UPPERHALF     (6 << SST25_SR_BP_SHIFT) /* Upper half */
#  define SST25_SR_BP_ALL           (7 << SST25_SR_BP_SHIFT) /* All sectors */
#define SST25_SR_AAI                (1 << 6)  /* Bit 6: Auto Address increment programming */
#define SST25_SR_SRWD               (1 << 7)  /* Bit 7: Status register write protect */

#define SST25_DUMMY                 0xa5

/* Chip Geometries ******************************************************************/
/* SST25VF512 capacity is 512Kbit (64Kbit x 8)   =  64Kb (8Kb x 8)*/
/* SST25VF010 capacity is 1Mbit   (128Kbit x 8)  = 128Kb (16Kb x 8*/
/* SST25VF520 capacity is 2Mbit   (256Kbit x 8)  = 256Kb (32Kb x 8) */
/* SST25VF540 capacity is 4Mbit   (512Kbit x 8)  = 512Kb (64Kb x 8) */
/* SST25VF080 capacity is 8Mbit   (1024Kbit x 8) =   1Mb (128Kb x 8) */
/* SST25VF016 capacity is 16Mbit  (2048Kbit x 8) =   2Mb (256Kb x 8) */
/* Not yet supported */

/* SST25VF032 capacity is 32Mbit  (4096Kbit x 8) =   4Mb (512kb x 8) */

#define SST25_VF032_SECTOR_SHIFT  12          /* Sector size 1 << 12 = 4Kb */
#define SST25_VF032_NSECTORS      1024        /* 1024 sectors x 4096 bytes/sector = 4Mb */

#ifdef CONFIG_SST25_SECTOR512                 /* Simulate a 512 byte sector */
#  define SST25_SECTOR_SHIFT      9           /* Sector size 1 << 9 = 512 bytes */
#  define SST25_SECTOR_SIZE       512         /* Sector size = 512 bytes */
#endif

/************************************************************************************
 * Private Types
 ************************************************************************************/

/* This type represents the state of the MTD device.  The struct mtd_dev_s must
 * appear at the beginning of the definition so that you can freely cast between
 * pointers to struct mtd_dev_s and struct sst25_dev_s.
 */

struct sst25_dev_s
{
  struct mtd_dev_s      mtd;         /* MTD interface */
  FAR struct spi_dev_s *dev;         /* Saved SPI interface instance */
  uint16_t              nsectors;    /* Number of erase sectors */
  uint8_t               sectorshift; /* Log2 of erase sector size */

#ifdef CONFIG_SST25_SECTOR512        /* Simulate a 512 byte sector */
  bool                  valid;       /* Buffered sector valid */
  uint16_t              esectno;     /* Erase sector number in the cache*/
  FAR uint8_t          *sector;      /* Allocated sector data */
#endif
};

/************************************************************************************
 * Private Function Prototypes
 ************************************************************************************/

/* Helpers */

static void sst25_lock(FAR struct spi_dev_s *dev);
static inline void sst25_unlock(FAR struct spi_dev_s *dev);
static inline int sst25_readid(FAR struct sst25_dev_s *priv);
static void sst25_waitwritecomplete(FAR struct sst25_dev_s *priv);
static inline void sst25_wren(FAR struct sst25_dev_s *priv);
static inline void sst25_wrdi(FAR struct sst25_dev_s *priv);
static inline void sst25_sectorerase(FAR struct sst25_dev_s *priv, off_t offset);
static inline int sst25_chiperase(FAR struct sst25_dev_s *priv);
static void sst25_byteread(FAR struct sst25_dev_s *priv, FAR uint8_t *buffer,
                           off_t address, size_t nbytes);
static void sst32_wordwrite(FAR struct sst25_dev_s *priv, FAR const uint8_t *buffer,
                            off_t address, size_t nwords);

#ifdef CONFIG_SST25_SECTOR512        /* Simulate a 512 byte sector */
static FAR uint8_t *sst25_cache(struct sst25_dev_s *priv, off_t address);
#endif

/* MTD driver methods */

static int sst25_erase(FAR struct mtd_dev_s *dev, off_t startblock, size_t nblocks);
static ssize_t sst25_bread(FAR struct mtd_dev_s *dev, off_t startblock,
                           size_t nblocks, FAR uint8_t *buf);
static ssize_t sst25_bwrite(FAR struct mtd_dev_s *dev, off_t startblock,
                            size_t nblocks, FAR const uint8_t *buf);
static ssize_t sst25_read(FAR struct mtd_dev_s *dev, off_t offset, size_t nbytes,
                          FAR uint8_t *buffer);
static int sst25_ioctl(FAR struct mtd_dev_s *dev, int cmd, unsigned long arg);

/************************************************************************************
 * Private Data
 ************************************************************************************/

/************************************************************************************
 * Private Functions
 ************************************************************************************/

/************************************************************************************
 * Name: sst25_lock
 ************************************************************************************/

static void sst25_lock(FAR struct spi_dev_s *dev)
{
  /* On SPI busses where there are multiple devices, it will be necessary to
   * lock SPI to have exclusive access to the busses for a sequence of
   * transfers.  The bus should be locked before the chip is selected.
   *
   * This is a blocking call and will not return until we have exclusiv access to
   * the SPI buss.  We will retain that exclusive access until the bus is unlocked.
   */

  SPI_LOCK(dev, true);

  /* After locking the SPI bus, the we also need call the setfrequency, setbits, and
   * setmode methods to make sure that the SPI is properly configured for the device.
   * If the SPI buss is being shared, then it may have been left in an incompatible
   * state.
   */

  SPI_SETMODE(dev, CONFIG_SST25_SPIMODE);
  SPI_SETBITS(dev, 8);
  (void)SPI_SETFREQUENCY(dev, CONFIG_SST25_SPIFREQUENCY);
}

/************************************************************************************
 * Name: sst25_unlock
 ************************************************************************************/

static inline void sst25_unlock(FAR struct spi_dev_s *dev)
{
  SPI_LOCK(dev, false);
}

/************************************************************************************
 * Name: sst25_readid
 ************************************************************************************/

static inline int sst25_readid(struct sst25_dev_s *priv)
{
  uint16_t manufacturer;
  uint16_t memory;
  uint16_t capacity;

  fvdbg("priv: %p\n", priv);

  /* Lock the SPI bus, configure the bus, and select this FLASH part. */

  sst25_lock(priv->dev);
  SPI_SELECT(priv->dev, SPIDEV_FLASH, true);

  /* Send the "Read ID (RDID)" command and read the first three ID bytes */

  (void)SPI_SEND(priv->dev, SST25_JEDEC_ID);
  manufacturer = SPI_SEND(priv->dev, SST25_DUMMY);
  memory       = SPI_SEND(priv->dev, SST25_DUMMY);
  capacity     = SPI_SEND(priv->dev, SST25_DUMMY);

  /* Deselect the FLASH and unlock the bus */

  SPI_SELECT(priv->dev, SPIDEV_FLASH, false);
  sst25_unlock(priv->dev);

  fvdbg("manufacturer: %02x memory: %02x capacity: %02x\n",
        manufacturer, memory, capacity);

  /* Check for a valid manufacturer and memory type */

  if (manufacturer == SST25_JEDEC_MANUFACTURER && memory == SST25_JEDEC_MEMORY_TYPE)
    {
      /* Okay.. is it a FLASH capacity that we understand?  This should be extended
       * support other members of the SST25 family.
       */

      if (capacity == SST25_JEDEC_MEMORY_CAPACITY)
        {
           /* Save the FLASH geometry */

           priv->sectorshift = SST25_VF032_SECTOR_SHIFT;
           priv->nsectors    = SST25_VF032_NSECTORS;
           return OK;
        }
    }

  return -ENODEV;
}

/************************************************************************************
 * Name: sst25_waitwritecomplete
 ************************************************************************************/

static void sst25_waitwritecomplete(struct sst25_dev_s *priv)
{
  uint8_t status;

  /* Are we the only device on the bus? */

#ifdef CONFIG_SPI_OWNBUS

  /* Select this FLASH part */

  SPI_SELECT(priv->dev, SPIDEV_FLASH, true);

  /* Send "Read Status Register (RDSR)" command */

  (void)SPI_SEND(priv->dev, SST25_RDSR);
  
  /* Loop as long as the memory is busy with a write cycle */

  do
    {
      /* Send a dummy byte to generate the clock needed to shift out the status */

      status = SPI_SEND(priv->dev, SST25_DUMMY);
    }
  while ((status & SST25_SR_BUSY) != 0);

  /* Deselect the FLASH */

  SPI_SELECT(priv->dev, SPIDEV_FLASH, false);

#else

  /* Loop as long as the memory is busy with a write cycle */

  do
    {
      /* Select this FLASH part */

      SPI_SELECT(priv->dev, SPIDEV_FLASH, true);

      /* Send "Read Status Register (RDSR)" command */

      (void)SPI_SEND(priv->dev, SST25_RDSR);

      /* Send a dummy byte to generate the clock needed to shift out the status */

      status = SPI_SEND(priv->dev, SST25_DUMMY);

      /* Deselect the FLASH */

      SPI_SELECT(priv->dev, SPIDEV_FLASH, false);

      /* Given that writing could take up to few tens of milliseconds, and erasing
       * could take more.  The following short delay in the "busy" case will allow
       * other peripherals to access the SPI bus.
       */

      if ((status & SST25_SR_BUSY) != 0)
        {
          sst25_unlock(priv->dev);
          usleep(1000);
          sst25_lock(priv->dev);
        }
    }
  while ((status & SST25_SR_BUSY) != 0);
#endif

  fvdbg("Complete\n");
}

/************************************************************************************
 * Name:  sst25_wren
 ************************************************************************************/

static inline void sst25_wren(struct sst25_dev_s *priv)
{
  /* Select this FLASH part */

  SPI_SELECT(priv->dev, SPIDEV_FLASH, true);

  /* Send "Write Enable (WREN)" command */

  (void)SPI_SEND(priv->dev, SST25_WREN);
  
  /* Deselect the FLASH */

  SPI_SELECT(priv->dev, SPIDEV_FLASH, false);
  fvdbg("Enabled\n");
}

/************************************************************************************
 * Name:  sst25_wrdi
 ************************************************************************************/

static inline void sst25_wrdi(struct sst25_dev_s *priv)
{
  /* Select this FLASH part */

  SPI_SELECT(priv->dev, SPIDEV_FLASH, true);

  /* Send "Write Disable (WRDI)" command */

  (void)SPI_SEND(priv->dev, SST25_WRDI);
  
  /* Deselect the FLASH */

  SPI_SELECT(priv->dev, SPIDEV_FLASH, false);
  fvdbg("Enabled\n");
}

/************************************************************************************
 * Name:  sst25_sectorerase
 ************************************************************************************/

static inline void sst25_sectorerase(struct sst25_dev_s *priv, off_t sector)
{
  off_t address = sector << priv->sectorshift;

  fvdbg("sector: %08lx\n", (long)sector);

  /* Wait for any preceding write or erase operation to complete. */

  sst25_waitwritecomplete(priv);

  /* Send write enable instruction */

  sst25_wren(priv);

  /* Select this FLASH part */

  SPI_SELECT(priv->dev, SPIDEV_FLASH, true);

  /* Send the "Sector Erase (SE)" instruction */

  (void)SPI_SEND(priv->dev, SST25_SE);

  /* Send the sector address high byte first. Only the most significant bits (those
   * corresponding to the sector) have any meaning.
   */

  (void)SPI_SEND(priv->dev, (address >> 16) & 0xff);
  (void)SPI_SEND(priv->dev, (address >> 8) & 0xff);
  (void)SPI_SEND(priv->dev, address & 0xff);

  /* Deselect the FLASH */

  SPI_SELECT(priv->dev, SPIDEV_FLASH, false);
  fvdbg("Erased\n");
}

/************************************************************************************
 * Name:  sst25_chiperase
 ************************************************************************************/

static inline int sst25_chiperase(struct sst25_dev_s *priv)
{
  fvdbg("priv: %p\n", priv);

  /* Wait for any preceding write or erase operation to complete. */

  sst25_waitwritecomplete(priv);

  /* Send write enable instruction */

  sst25_wren(priv);

  /* Select this FLASH part */

  SPI_SELECT(priv->dev, SPIDEV_FLASH, true);

  /* Send the "Chip Erase (CE)" instruction */

  (void)SPI_SEND(priv->dev, SST25_CE);

  /* Deselect the FLASH */

  SPI_SELECT(priv->dev, SPIDEV_FLASH, false);
  fvdbg("Return: OK\n");
  return OK;
}

/************************************************************************************
 * Name: sst25_byteread
 ************************************************************************************/

static void sst25_byteread(FAR struct sst25_dev_s *priv, FAR uint8_t *buffer,
                           off_t address, size_t nbytes)
{
  fvdbg("address: %08lx nbytes: %d\n", (long)address, (int)nbytes);

  /* Wait for any preceding write or erase operation to complete. */

  sst25_waitwritecomplete(priv);

  /* Select this FLASH part */

  SPI_SELECT(priv->dev, SPIDEV_FLASH, true);

  /* Send "Read from Memory " instruction */

  (void)SPI_SEND(priv->dev, SST25_FAST_READ);

  /* Send the address high byte first. */

  (void)SPI_SEND(priv->dev, (address >> 16) & 0xff);
  (void)SPI_SEND(priv->dev, (address >> 8) & 0xff);
  (void)SPI_SEND(priv->dev, address & 0xff);

  /* Send a dummy byte */

  (void)SPI_SEND(priv->dev, SST25_DUMMY);

  /* Then read all of the requested bytes */

  SPI_RECVBLOCK(priv->dev, buffer, nbytes);

  /* Deselect the FLASH */

  SPI_SELECT(priv->dev, SPIDEV_FLASH, false);
}

/************************************************************************************
 * Name:  sst32_wordwrite
 ************************************************************************************/

static void sst32_wordwrite(struct sst25_dev_s *priv, FAR const uint8_t *buffer,
                            off_t address, size_t nwords)
{
  fvdbg("address: %08lx nwords: %d\n", (long)address, (int)nwords);
  DEBUGASSERT(priv && buffer);

  /* Wait for any preceding write or erase operation to complete. */

  sst25_waitwritecomplete(priv);

  /* Enable the write access to the FLASH */

  sst25_wren(priv);
  
  /* Select this FLASH part */

  SPI_SELECT(priv->dev, SPIDEV_FLASH, true);

  /* Send "Auto Address Increment (AAI)" command */

  (void)SPI_SEND(priv->dev, SST25_AAI);

  /* Send the page address high byte first. */

  (void)SPI_SEND(priv->dev, (address >> 16) & 0xff);
  (void)SPI_SEND(priv->dev, (address >> 8) & 0xff);
  (void)SPI_SEND(priv->dev, address & 0xff);

  /* Then write one 16-bit word */

  SPI_SNDBLOCK(priv->dev, buffer, 2);
  
  /* Deselect the FLASH: Chip Select high */

  SPI_SELECT(priv->dev, SPIDEV_FLASH, false);
  buffer += 2;

  /* Now loop, writing 16-bits of data on each pass through the loop until all
   * of the words have been transferred.
   */

  for (nwords--; nwords > 0; nwords--)
    {
      /* Select this FLASH part */

      SPI_SELECT(priv->dev, SPIDEV_FLASH, true);

      /* Wait for the preceding write to complete. */

      sst25_waitwritecomplete(priv);

      /* Send "Auto Address Increment (AAI)" command with no address */

      (void)SPI_SEND(priv->dev, SST25_AAI);

      /* Then write one 16-bit word */

      SPI_SNDBLOCK(priv->dev, buffer, 2);
      buffer += 2;

      /* Deselect the FLASH: Chip Select high */

      SPI_SELECT(priv->dev, SPIDEV_FLASH, false);
    }

  /* Disable writing */

  sst25_wrdi(priv);
  fvdbg("Written\n");
}

/************************************************************************************
 * Name: sst25_cache
 ************************************************************************************/

#ifdef CONFIG_SST25_SECTOR512
static FAR uint8_t *sst25_cache(struct sst25_dev_s *priv, off_t sector)
{
  off_t esectno;
  off_t address;
  int   shift;
  int   index;
 
  /* Convert from the 512 byte sector to the erase sector size of the device.  For
   * exmample, if the actual erase sector size if 4Kb (1 << 12), then we first
   * shift to the right by 3 to get the sector number in 4096 increments.
   */

  shift    = priv->sectorshift - SST25_SECTOR_SHIFT;
  esectno  = sector >> shift;
  fvdbg("sector: %ld esectno: %d shift=%d\n", sector, sectno, shift);

  /* Check if this erase block is alread in the cache */

  if (!priv->valid || esectno != priv->esectno)
    {
      /* Read the erase block into the cache */

      sst325_byteread(priv, priv->sector, (esectno << priv->sectorshift), 1 << priv->sectorshift);

      /* Mark the sector as cached */

      priv->valid   = true;
      priv->esectno = esectno;
    }

  /* Get the index to the 512 sector in the erase block that holds the argument */

  index = sector & ((1 << shift) - 1);

  /* Return the address in the cache that holds this sector */

  return &priv->sector[index << SST25_SECTOR_SHIFT];
}
#endif

/************************************************************************************
 * Name: sst25_erase
 ************************************************************************************/

static int sst25_erase(FAR struct mtd_dev_s *dev, off_t startblock, size_t nblocks)
{
  FAR struct sst25_dev_s *priv = (FAR struct sst25_dev_s *)dev;
  size_t blocksleft = nblocks;

  fvdbg("startblock: %08lx nblocks: %d\n", (long)startblock, (int)nblocks);

  /* Lock access to the SPI bus until we complete the erase */

  sst25_lock(priv->dev);
  while (blocksleft-- > 0)
    {
      /* Erase each sector */

      sst25_sectorerase(priv, startblock);
      startblock++;
    }

  sst25_unlock(priv->dev);
  return (int)nblocks;
}

/************************************************************************************
 * Name: sst25_bread
 ************************************************************************************/

static ssize_t sst25_bread(FAR struct mtd_dev_s *dev, off_t startblock, size_t nblocks,
                          FAR uint8_t *buffer)
{
  FAR struct sst25_dev_s *priv = (FAR struct sst25_dev_s *)dev;
  ssize_t nbytes;

  fvdbg("startblock: %08lx nblocks: %d\n", (long)startblock, (int)nblocks);

  /* On this device, we can handle the block read just like the byte-oriented read */

#ifdef CONFIG_SST25_SECTOR512
  nbytes = sst25_read(dev, startblock << SST25_SECTOR_SHIFT, nblocks << SST25_SECTOR_SHIFT, buffer);
  if (nbytes > 0)
    {
      return nbytes >> SST25_SECTOR_SHIFT;
    }
#else
  nbytes = sst25_read(dev, startblock << priv->sectorshift, nblocks << priv->sectorshift, buffer);
  if (nbytes > 0)
    {
      return nbytes >> priv->sectorshift;
    }
#endif

  return (int)nbytes;
}

/************************************************************************************
 * Name: sst25_bwrite
 ************************************************************************************/

static ssize_t sst25_bwrite(FAR struct mtd_dev_s *dev, off_t startblock, size_t nblocks,
                           FAR const uint8_t *buffer)
{
  FAR struct sst25_dev_s *priv = (FAR struct sst25_dev_s *)dev;
  size_t nwords;

  fvdbg("startblock: %08lx nblocks: %d\n", (long)startblock, (int)nblocks);

  /* Lock the SPI bus and write all of the pages to FLASH */

  sst25_lock(priv->dev);
#ifdef CONFIG_SST25_SECTOR512
  nwords = (nblocks << (SST25_SECTOR_SHIFT - 1));
  sst32_wordwrite(priv, buffer, startblock << SST25_SECTOR_SHIFT, nwords);
#else
  nwords = (nblocks << (priv->sectorshift - 1));
  sst32_wordwrite(priv, buffer, startblock << priv->sectorshift, nwords);
#endif
  sst25_unlock(priv->dev);

  return nblocks;
}

/************************************************************************************
 * Name: sst25_read
 ************************************************************************************/

static ssize_t sst25_read(FAR struct mtd_dev_s *dev, off_t offset, size_t nbytes,
                         FAR uint8_t *buffer)
{
  FAR struct sst25_dev_s *priv = (FAR struct sst25_dev_s *)dev;

  fvdbg("offset: %08lx nbytes: %d\n", (long)offset, (int)nbytes);

  /* Lock the SPI bus and select this FLASH part */

  sst25_lock(priv->dev);
  sst25_byteread(priv, buffer, offset, nbytes);
  sst25_unlock(priv->dev);

  fvdbg("return nbytes: %d\n", (int)nbytes);
  return nbytes;
}

/************************************************************************************
 * Name: sst25_ioctl
 ************************************************************************************/

static int sst25_ioctl(FAR struct mtd_dev_s *dev, int cmd, unsigned long arg)
{
  FAR struct sst25_dev_s *priv = (FAR struct sst25_dev_s *)dev;
  int ret = -EINVAL; /* Assume good command with bad parameters */

  fvdbg("cmd: %d \n", cmd);

  switch (cmd)
    {
      case MTDIOC_GEOMETRY:
        {
          FAR struct mtd_geometry_s *geo = (FAR struct mtd_geometry_s *)((uintptr_t)arg);
          if (geo)
            {
              /* Populate the geometry structure with information need to know
               * the capacity and how to access the device.
               *
               * NOTE: that the device is treated as though it where just an array
               * of fixed size blocks.  That is most likely not true, but the client
               * will expect the device logic to do whatever is necessary to make it
               * appear so.
               */

#ifdef CONFIG_SST25_SECTOR512
              geo->blocksize    = (1 << SST25_SECTOR_SHIFT);
#else
              geo->blocksize    = (1 << priv->sectorshift);
#endif
              geo->erasesize    = (1 << priv->sectorshift);
              geo->neraseblocks = priv->nsectors;
              ret               = OK;

              fvdbg("blocksize: %d erasesize: %d neraseblocks: %d\n",
                    geo->blocksize, geo->erasesize, geo->neraseblocks);
            }
        }
        break;

      case MTDIOC_BULKERASE:
        {
            /* Erase the entire device */

            sst25_lock(priv->dev);
            ret = sst25_chiperase(priv);
            sst25_unlock(priv->dev);
        }
        break;
 
      case MTDIOC_XIPBASE:
      default:
        ret = -ENOTTY; /* Bad command */
        break;
    }

  fvdbg("return %d\n", ret);
  return ret;
}

/************************************************************************************
 * Public Functions
 ************************************************************************************/

/************************************************************************************
 * Name: sst25_initialize
 *
 * Description:
 *   Create an initialize MTD device instance.  MTD devices are not registered
 *   in the file system, but are created as instances that can be bound to
 *   other functions (such as a block or character driver front end).
 *
 ************************************************************************************/

FAR struct mtd_dev_s *sst25_initialize(FAR struct spi_dev_s *dev)
{
  FAR struct sst25_dev_s *priv;
  int ret;

  fvdbg("dev: %p\n", dev);

  /* Allocate a state structure (we allocate the structure instead of using
   * a fixed, static allocation so that we can handle multiple FLASH devices.
   * The current implementation would handle only one FLASH part per SPI
   * device (only because of the SPIDEV_FLASH definition) and so would have
   * to be extended to handle multiple FLASH parts on the same SPI bus.
   */

  priv = (FAR struct sst25_dev_s *)kzalloc(sizeof(struct sst25_dev_s));
  if (priv)
    {
      /* Initialize the allocated structure */

      priv->mtd.erase  = sst25_erase;
      priv->mtd.bread  = sst25_bread;
      priv->mtd.bwrite = sst25_bwrite;
      priv->mtd.read   = sst25_read;
      priv->mtd.ioctl  = sst25_ioctl;
      priv->dev        = dev;

      /* Deselect the FLASH */

      SPI_SELECT(dev, SPIDEV_FLASH, false);

      /* Identify the FLASH chip and get its capacity */

      ret = sst25_readid(priv);
      if (ret != OK)
        {
          /* Unrecognized! Discard all of that work we just did and return NULL */

          fdbg("Unrecognized\n");
          kfree(priv);
          priv = NULL;
        }
#ifdef CONFIG_SST25_SECTOR512        /* Simulate a 512 byte sector */
      else
        {
          /* Allocate a sector buffer */

          priv->sector = (FAR uint8_t *)kmalloc(1 << priv->sectorshift);
          if (!priv->sector)
            {
              /* Allocation failed! Discard all of that work we just did and return NULL */

              fdbg("Allocation failed\n");
              kfree(priv);
              priv = NULL;
            }
        }
#endif
    }

  /* Return the implementation-specific state structure as the MTD device */

  fvdbg("Return %p\n", priv);
  return (FAR struct mtd_dev_s *)priv;
}