/*********************************************************************************
 *      Copyright:  (C) 2023 LingYun IoT System Studio
 *                  All rights reserved.
 *
 *       Filename:  at24c.c
 *    Description:  This file is AT24Cxx EEPROM code
 *
 *        Version:  1.0.0(10/08/23)
 *         Author:  Guo Wenxue <guowenxue@gmail.com>
 *      ChangeLog:  1, Release initial version on "10/08/23 17:52:00"
 *
 * Pin connection:
 *                 W25QXX       Raspberry Pi 40Pin
 *                   VCC   <--->   Pin#1 (3.3V)
 *                   CS    <--->   Pin#24(CS)
 *                   DO    <--->   Pin#21(MISO)
 *                   GND   <--->   Pin#9 (GND)
 *                   CLK   <--->   Pin#23(SCLK)
 *                   DI    <--->   Pin#19(MOSI)
 *
 * /boot/config.txt:
 *                  dtparam=spi=on
 *
 ********************************************************************************/

#include <stdint.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <getopt.h>
#include <fcntl.h>
#include <time.h>
#include <sys/ioctl.h>
#include <linux/ioctl.h>
#include <sys/stat.h>
#include <linux/types.h>
#include <linux/spi/spidev.h>

#include "w25qflash.h"

#define CONFIG_SPINOR_DEBUG

#ifdef CONFIG_SPINOR_DEBUG
#include <stdio.h>
#define spinor_print(format,args...)    printf(format, ##args)
#else
#define spinor_print(format,args...)    do{} while(0)
#endif

#define spinor_Delay(delay)             usleep(delay*1000)

/*+-----------------------+
 *|   Entry Functions     |
 *+-----------------------+*/

void dump_buf(const char *prompt, char *buffer, size_t length);

int main (int argc, char **argv)
{
    spinor_test();

    return 0;
}


/*+-----------------------+
 *|   SPI API Functions   |
 *+-----------------------+*/

#define SPI_DEV                         "/dev/spidev0.0"
#define SPI_BITS                        8
#define SPI_MODE                        0//(SPI_CPHA|SPI_CPOL)
#define SPI_SPEED                       500000

#define SPI_DUMMY_BYTE                  0xA5

void spinor_dev_init(struct spi_info *spi)
{
    uint8_t             bits = SPI_BITS;
    uint32_t            speed = SPI_SPEED;
    uint32_t            mode = SPI_MODE;
    uint32_t            request;
    int                 ret;

    spi->hspi = open(SPI_DEV, O_RDWR);
    if (spi->hspi < 0)
    {
        spinor_print("ERROR: open device %s failure: %s\r\n", SPI_DEV, strerror(errno));
        return ;
    }

    /*
     * spi mode
     */
    request = mode;
    if( ioctl(spi->hspi, SPI_IOC_WR_MODE32, &mode) < 0 )
    {
        spinor_print("ERROR: can't set spi mode\n");
        return ;
    }

    if( ioctl(spi->hspi, SPI_IOC_RD_MODE32, &mode) < 0 )
    {
        spinor_print("ERROR: can't get spi mode\n");
        return ;
    }

    if (request != mode)
    {
        spinor_print("WARNING: device does not support requested mode 0x%x\n", request);
    }

    /*
     * bits per word
     */
    if( ioctl(spi->hspi, SPI_IOC_WR_BITS_PER_WORD, &bits) < 0 )
    {
        spinor_print("ERROR: can't set bits per word");
        return ;
    }

    if( ioctl(spi->hspi, SPI_IOC_RD_BITS_PER_WORD, &bits) < 0 )
    {
        spinor_print("ERROR: can't get bits per word");
        return ;
    }

    /*
     * max speed hz
     */
    if( ioctl(spi->hspi, SPI_IOC_WR_MAX_SPEED_HZ, &speed) < 0 )
    {
        spinor_print("ERROR: can't set max speed hz");
        return ;
    }

    if( ioctl(spi->hspi, SPI_IOC_RD_MAX_SPEED_HZ, &speed) < 0 )
    {
        spinor_print("ERROR: can't get max speed hz");
        return ;
    }

    printf("spi mode: 0x%x\n", mode);
    printf("bits per word: %u\n", bits);
    printf("max speed: %u Hz (%u kHz)\n", speed, speed/1000);
}

void spi_cs_enable(struct spi_info *spi)
{
    /*
     * No need set CS in Linux because the device name /dev/spi0.0
     * will choose the first slave device, second slave is spi0.1
     */
    (void)0;
}

void spi_cs_disable(struct spi_info *spi)
{
    (void)0;
}

void spi_xcmd(struct spi_info *spi, uint8_t command)
{
    uint8_t                 rxbyte;
    struct spi_ioc_transfer tr = {
        .tx_buf = (unsigned long)&command,
        .rx_buf = (unsigned long)&rxbyte,
        .len = 1,
        .delay_usecs = 0,
        .speed_hz = SPI_SPEED,
        .bits_per_word = SPI_BITS,
    };

    spi->select(spi);

    if( ioctl(spi->hspi, SPI_IOC_MESSAGE(1), &tr) < 0 )
    {
        spinor_print("ERROR: can't send spi message:%s\n", strerror(errno));
    }

    spi->deselect(spi);

    return;
}

void spi_xfer(struct spi_info *spi, uint8_t *send_buf, uint8_t *recv_buf, int bytes)
{
    struct spi_ioc_transfer tr = {
        .tx_buf = (unsigned long)send_buf,
        .rx_buf = (unsigned long)recv_buf,
        .len = bytes,
        .delay_usecs = 0,
        .speed_hz = SPI_SPEED,
        .bits_per_word = SPI_BITS,
    };

    spi->select(spi);

    if( ioctl(spi->hspi, SPI_IOC_MESSAGE(1), &tr) < 0 )
    {
        spinor_print("ERROR: can't send spi message:%s\n", strerror(errno));
    }

    spi->deselect(spi);

    return;
}

#define SPI_INFO(_hspi, _cs_gpio, _cs_pin) {\
    .hspi       = _hspi,            \
    .select     = spi_cs_enable,    \
    .deselect   = spi_cs_disable,   \
    .xcmd       = spi_xcmd,         \
    .xfer       = spi_xfer,         \
}

static struct spi_info spinor_spi = SPI_INFO(-1, W25Q_CS_PORT, W25Q_CS_PIN);


/*+-----------------------+
 *|  W25Q SPI Norflash ID |
 *+-----------------------+*/

#define W25Q_PAGSIZE            256     /* 1Page=256B */
#define W25Q_SECSIZE            4096    /* 1Sector=16Pages=4KB */
#define W25Q_BLKSIZE            65536   /* 1Block=16Sector=64KB */

#define ARRAY_SIZE(x)           (sizeof(x)/sizeof(x[0]))

/* JEDEC ID the 3rd bytes is the storage capacity */
#pragma GCC diagnostic ignored "-Wshift-count-overflow"
#define CAPCITY_ID(id)          (1UL<<(id&0xFF))
#define NOR_INFO(_name, _jedec_id) \
    .name       = _name,                                \
.jedec_id   = _jedec_id,                            \
.block_size = W25Q_BLKSIZE,                         \
.sector_size= W25Q_SECSIZE,                         \
.page_size  = W25Q_PAGSIZE,                         \
.capacity   = CAPCITY_ID(_jedec_id),                \
.n_blocks   = CAPCITY_ID(_jedec_id)/W25Q_BLKSIZE,   \
.n_sectors  = CAPCITY_ID(_jedec_id)/W25Q_SECSIZE,   \
.n_pages    = CAPCITY_ID(_jedec_id)/W25Q_PAGSIZE,   \

static struct flash_info spinor_ids[] = {
    { NOR_INFO("W25Q512", 0xef4020) },
    { NOR_INFO("W25Q256", 0xef4019) },
    { NOR_INFO("W25Q128", 0xef4018) },
    { NOR_INFO("W25Q64",  0xef4017) },
    { NOR_INFO("W25Q32",  0xef4016) },
    { NOR_INFO("W25Q16",  0xef4015) },
    { NOR_INFO("W25Q80",  0xef4014) },
    { NOR_INFO("W25Q40",  0xef4013) },
    { NOR_INFO("W25Q20",  0xef4012) },
    { NOR_INFO("W25Q10",  0xef4011) },
};

/*+-------------------------------+
 *|   SPI Norflash HighLevel API  |
 *+-------------------------------+*/

/* SPI Norflash API test function */
void spinor_test(void)
{
    spinor_info_t          spinor;
    int                    i;
    uint8_t                buf[W25Q_PAGSIZE*2];

    if( spinor_init(&spinor) < 0 )
        return ;

    //spinor_erase_chip(&spinor);
    //spinor_erase_block(&spinor, 1, W25Q_BLKSIZE);
    spinor_erase_sector(&spinor, 1, W25Q_SECSIZE);

    memset(buf, 0, sizeof(buf));
    spinor_read(&spinor, 0, buf, sizeof(buf));
    dump_buf("<<<Read data after erase:\n", (char *)buf, sizeof(buf));

    /* Read/Write data test on address not page align */
    for(i=0; i<sizeof(buf); i++)
        buf[i] = i;
    spinor_write(&spinor, 16, buf, W25Q_PAGSIZE);

    memset(buf, 0, sizeof(buf));
    spinor_read(&spinor, 0, buf, W25Q_PAGSIZE*2);
    dump_buf("<<<Read data after write:\n", (char *)buf, sizeof(buf));

    return ;
}

/* Initial SPI and detect the flash chip. */
int spinor_init(struct spinor_info *spinor)
{
    spinor->spi = &spinor_spi;

    spinor_dev_init(spinor->spi);

    if( !spinor_detect_by_jedec(spinor) )
        return -1;

    printf("Norflash %s detected, capacity %llu KB, %u blocks, %u sectors, %u pages.\r\n",
            spinor->flash->name, spinor->flash->capacity>>10,
            spinor->flash->n_blocks, spinor->flash->n_sectors, spinor->flash->n_pages);

    return 0;
}

/* Description:  Erase whole flash chip.
 * Reference  :  P60, 8.2.32 Chip Erase (C7h / 60h)
 */
int spinor_erase_chip(struct spinor_info *spinor)
{
    struct spi_info *spi = spinor->spi;

    while (spinor->lock == 1)
        spinor_Delay(1);

    spinor->lock = 1;

#ifdef CONFIG_SPINOR_DEBUG
    printf("Norflash EraseChip Begin...\r\n");
#endif

    spinor_write_enable(spi);

    spi->xcmd(spi, SPINOR_OP_CHIP_ERASE);
    spinor_WaitForWriteEnd(spi);

#ifdef CONFIG_SPINOR_DEBUG
    printf("Norflash EraseChip done.\r\n");
#endif

    spinor_Delay(10);
    spinor->lock = 0;

    return 0;
}

/* Description:  Erase blocks by 64KiB,
 * Reference  :  P59, 8.2.31 64KB Block Erase with 4-Byte Address (DCh)
 *  @address is the erase start physical address, which can be not block alignment such as 0x10001.
 *  @size is the erase size, which can be larger than a block such as 4097, and it will erase 2 blocks;
 */
int spinor_erase_block(struct spinor_info *spinor, uint32_t address, uint32_t size)
{
    struct spi_info    *spi = spinor->spi;
    struct flash_info  *flash = spinor->flash;
    uint32_t            block, first, last;
    uint32_t            addr;
    uint8_t             buf[5];
    int                 bytes = 0;

    while (spinor->lock == 1)
        spinor_Delay(1);

    spinor->lock = 1;

    /* find first and last erase block */
    first = address / flash->block_size;
    last  = (address+size-1) / flash->block_size;

#ifdef CONFIG_SPINOR_DEBUG
    printf("Norflash Erase %d Bytes Block@0x%x Begin...\r\n", size, address);
#endif

    /* start erase all the blocks */
    for( block=first; block<=last; block++)
    {
        addr = block * flash->sector_size;
#ifdef CONFIG_SPINOR_DEBUG
        printf("Norflash Erase Block@%x ...\r\n", addr);
#endif
        spinor_WaitForWriteEnd(spi);
        spinor_write_enable(spi);

        if (spinor->flash->n_blocks >= 512 ) /* larger than W25Q256 */
        {
            buf[bytes++] = SPINOR_OP_BE_4K_4B;
            buf[bytes++] = (addr & 0xFF000000) >> 24;
        }
        else
        {
            buf[bytes++] = SPINOR_OP_BE_4K;
        }
        buf[bytes++] = (addr & 0xFF0000) >> 16 ;
        buf[bytes++] = (addr & 0xFF00) >> 8 ;
        buf[bytes++] = (addr & 0xFF);

        spi->xfer(spi, buf, NULL, bytes);

        spinor_WaitForWriteEnd(spi);
    }

#ifdef CONFIG_SPINOR_DEBUG
    printf("Norflash EraseBlock@0x%x done.\r\n", address);
    spinor_Delay(100);
#endif

    spinor_Delay(1);
    spinor->lock = 0;

    return 0;
}

/* Description:  Erase sectors by 4KiB
 * Reference  :  P56, 8.2.28 Sector Erase with 4-Byte Address (21h)
 *  @address is the erase start physical address, which can be not sector alignment such as 0x1001.
 *  @size is the erase size, which can be larger than a sector such as 4097, and it will erase 2 sectors;
 */
int spinor_erase_sector(struct spinor_info *spinor, uint32_t address, uint32_t size)
{
    struct spi_info    *spi = spinor->spi;
    struct flash_info  *flash = spinor->flash;
    uint32_t            sector, first, last;
    uint32_t            addr;
    uint8_t             buf[5];
    int                 bytes = 0;

    while (spinor->lock == 1)
        spinor_Delay(1);

    spinor->lock = 1;

    /* find first and last erase sector */
    first = address / flash->sector_size;
    last  = (address+size-1) / flash->sector_size;

#ifdef CONFIG_SPINOR_DEBUG
    printf("Norflash Erase %d Bytes Sector@0x%x Begin...\r\n", size, address);
#endif

    /* start erase all the sectors */
    for( sector=first; sector<=last; sector++)
    {
        addr = sector * flash->sector_size;
#ifdef CONFIG_SPINOR_DEBUG
        printf("Norflash Erase Sector@%x ...\r\n", addr);
#endif

        spinor_WaitForWriteEnd(spi);
        spinor_write_enable(spi);

        if (spinor->flash->n_blocks >= 512 ) /* larger than W25Q256 */
        {
            buf[bytes++] = SPINOR_OP_SE_4B;
            buf[bytes++] = (addr & 0xFF000000) >> 24;
        }
        else
        {
            buf[bytes++] = SPINOR_OP_SE;
        }
        buf[bytes++] = (addr & 0xFF0000) >> 16 ;
        buf[bytes++] = (addr & 0xFF00) >> 8 ;
        buf[bytes++] = (addr & 0xFF);

        spi->xfer(spi, buf, NULL, bytes);

        spinor_WaitForWriteEnd(spi);
    }

#ifdef CONFIG_SPINOR_DEBUG
    printf("Norflash EraseSector@0x%x done.\r\n", address);
#endif

    spinor_Delay(1);
    spinor->lock = 0;

    return 0;
}

/* P32: 10.2.14 Page Program (02h) */
int spinor_write(struct spinor_info *spinor, uint32_t address, uint8_t *data, uint32_t size)
{
    struct spi_info    *spi = spinor->spi;
    struct flash_info  *flash = spinor->flash;
    uint32_t            page, first, last;
    uint32_t            addr, ofset, len;
    uint8_t             buf[W25Q_PAGSIZE+5];
    int                 bytes = 0;

    if( address+size > spinor->flash->capacity )
        return -1;

    while (spinor->lock == 1)
        spinor_Delay(1);

    spinor->lock = 1;

    /* find first and last write page */
    first = address / flash->page_size;
    last  = (address+size-1) / flash->page_size;

#ifdef CONFIG_SPINOR_DEBUG
    printf("Norflash Write %d Bytes to addr@0x%x Begin...\r\n", size, address);
#endif

    /* address in page and offset in buffer */
    addr = address;
    ofset = 0;

    /* start write all the pages */
    for( page=first; page<=last; page++)
    {
        len = flash->page_size - (addr%flash->page_size);
        len = len > size ? size : len;
        bytes = 0;

#ifdef CONFIG_SPINOR_DEBUG
        printf("Norflash write addr@0x%x, %u bytes\r\n", addr, len);
#endif

        spinor_WaitForWriteEnd(spi);
        spinor_write_enable(spi);

        if (spinor->flash->n_blocks >= 512 )
        {
            buf[bytes++] = SPINOR_OP_PP_4B;
            buf[bytes++] = (addr & 0xFF000000) >> 24;
        }
        else
        {
            buf[bytes++] = SPINOR_OP_PP;
        }
        buf[bytes++] = (addr & 0xFF0000) >> 16 ;
        buf[bytes++] = (addr & 0xFF00) >> 8 ;
        buf[bytes++] = (addr & 0xFF);

        /* send command and data */
        memcpy(&buf[bytes], data+ofset, len);
        bytes += len;
        spi->xfer(spi, buf, NULL, bytes);

        spinor_WaitForWriteEnd(spi);

        addr  += len;
        ofset += len;
        size  -= len;
    }

#ifdef CONFIG_SPINOR_DEBUG
    printf("Norflash WriteByte@0x%x done.\r\n", address);
#endif

    spinor_Delay(1);
    spinor->lock = 0;

    return 0;
}

/* Description:  The Fast Read instruction can read the entire memory chip.
 * Reference  :  P41, 8.2.13 Fast Read with 4-Byte Address (0Ch)
 *  @address is the read start physical address, which can be not page alignment such as 0x101.
 *  @size is the read size, which can be larger than a page such as 257, and it will read 2 pages;
 */
int spinor_read(struct spinor_info *spinor, uint32_t address, uint8_t *data, uint32_t size)
{
    struct spi_info     *spi = spinor->spi;
    uint8_t             buf[W25Q_PAGSIZE+6];
    int                 bytes = 0;
    int                 ofset;
    uint32_t            addr = address;

    if( address+size > spinor->flash->capacity )
        return -1;

    while (spinor->lock == 1)
        spinor_Delay(1);

    spinor->lock = 1;

#ifdef CONFIG_SPINOR_DEBUG
    printf("Norflash Read %d Bytes from addr@0x%x Begin...\r\n", size, address);
#endif

    while( size > 0 )
    {
        bytes = size>W25Q_PAGSIZE ? W25Q_PAGSIZE : size;
        memset(buf, SPI_DUMMY_BYTE, sizeof(buf));
        ofset = 0;

#ifdef CONFIG_SPINOR_DEBUG
        printf("Norflash read addr@0x%x, %d bytes\r\n", addr, bytes);
#endif

        /* send instruction and address */
        if (spinor->flash->n_blocks >= 512 )
        {
            buf[ofset++] = SPINOR_OP_READ_FAST_4B;
            buf[ofset++] = (addr & 0xFF000000) >> 24;
        }
        else
        {
            buf[ofset++] = SPINOR_OP_READ_FAST;
        }
        buf[ofset++] = (addr & 0xFF0000) >> 16 ;
        buf[ofset++] = (addr & 0xFF00) >> 8 ;
        buf[ofset++] = (addr & 0xFF);

        ofset += 1; /* Skip first dummy byte */

        /* Send command and read data out */
        spi->xfer(spi, buf, buf, ofset+bytes);
        memcpy(data, &buf[ofset], bytes);

        size -= bytes;
        addr += bytes;
        data += bytes;
    }

#ifdef CONFIG_SPINOR_DEBUG
    printf("Norflash ReadBytes@0x%x done.\r\n", address);
#endif
    spinor->lock = 0;

    return 0;
}

/*+-------------------------------+
 *|   SPI Norflash LowLevel API   |
 *+-------------------------------+*/

/* Detect the norflash by JEDEC ID */
int spinor_detect_by_jedec(struct spinor_info *spinor)
{
    uint32_t            jedec_id;
    int                 i, found = 0;

    jedec_id = spinor_read_jedecid(spinor->spi);

    for(i=0; i<ARRAY_SIZE(spinor_ids); i++)
    {
        if(spinor_ids[i].jedec_id == jedec_id)
        {
            found = 1;
            spinor->flash = &spinor_ids[i];
            break;
        }
    }

    printf("Detect JEDEC ID[0x%x], Norflash %s found\r\n", jedec_id, found?spinor->flash->name:"not");
    return found;
}

/* Description:  Read the chipset UNIQUE ID.
 * Reference  :  P68, 8.2.40 Read Unique ID Number (4Bh)
 */
int spinor_read_uniqid(struct spi_info *spi, uint8_t *uniq_id)
{
    uint8_t              i;
    uint8_t              buf[13]; /* Instruction(1B) + Dummy(4B) + UID(8B)*/

    if( !uniq_id )
        return -1;

    buf[0] = SPINOR_OP_RDUID;
    spi->xfer(spi, buf, buf, sizeof(buf));

    /* Skip 4 bytes dummy bytes */
    for (i=0; i<8; i++)
    {
        uniq_id[i] = buf[5+i];
    }

    return 0;
}

/* Description:  Read the chipset JEDEC ID.
 * Reference  :  P69, 8.2.41 Read JEDEC ID (9Fh)
 */
uint32_t spinor_read_jedecid(struct spi_info *spi)
{
    uint32_t            jedec_id = 0x0;
    uint8_t             buf[4];

    buf[0] = SPINOR_OP_RDID;
    spi->xfer(spi, buf, buf, sizeof(buf));
    jedec_id = (buf[1] << 16) | (buf[2] << 8) | buf[3];

    return jedec_id;
}

/* Description:  Write Enable
 * Reference  :  P31, 8.2.1 Write Enable (06h)
 */
void spinor_write_enable(struct spi_info *spi)
{
    spi->xcmd(spi, SPINOR_OP_WREN);

    spinor_Delay(1);
}

/* Description:  Write Disable
 * Reference  :  P32, 8.2.3 Write Disable (04h)
 */
void spinor_write_disable(struct spi_info *spi)
{
    spi->xcmd(spi, SPINOR_OP_WRDI);

    spinor_Delay(1);
}

/* Description:  Read Status Register
 * Reference  :  P32, 8.2.4 Read Status Register-1 (05h), Status Register-2 (35h) & Status Register-3 (15h)
 */
uint8_t spinor_read_status_reg(struct spi_info *spi, uint8_t reg)
{
    uint8_t cmd[REG_STATUS_MAX] = { SPINOR_OP_RDSR1 , SPINOR_OP_RDSR2, SPINOR_OP_RDSR3 }; /* Status Register 1~3 */
    uint8_t buf[2];

    if( reg>= REG_STATUS_MAX )
        return 0xFF;

    buf[0] = cmd[reg];
    buf[1] = SPI_DUMMY_BYTE;
    spi->xfer(spi, buf, buf, sizeof(buf));

    return buf[1];
}

/* Description:  Write Status Register
 * Reference  :  P33, 8.2.5 Write Status Register-1 (01h), Status Register-2 (31h) & Status Register-3 (11h)
 */
void spinor_write_status_reg(struct spi_info *spi, uint8_t reg, uint8_t value)
{
    uint8_t cmd[REG_STATUS_MAX] = { SPINOR_OP_WRSR1 , SPINOR_OP_WRSR2, SPINOR_OP_WRSR3 }; /* Status Register 1~3 */
    uint8_t buf[2];

    if( reg>= REG_STATUS_MAX )
        return ;

    buf[0] = cmd[reg];
    buf[1] = value;
    spi->xfer(spi, buf, buf, sizeof(buf));
}

/* Description:  Wait flash program/erase finished by read Status Register for BUSY bit
 * Reference  :  P15, 7.1 Status Registers
 */
void spinor_WaitForWriteEnd(struct spi_info *spi)
{
    uint8_t buf[2];

    spinor_Delay(1);

    do
    {
        buf[0] = SPINOR_OP_RDSR1;
        buf[1] = SPI_DUMMY_BYTE;
        spi->xfer(spi, buf, buf, sizeof(buf));

        spinor_Delay(1);
    } while ((buf[1] & 0x01) == 0x01);
}

/*+----------------------+
 *|    Misc functions    |
 *+----------------------+*/

void print_buf(const char *prompt, uint8_t *buf, int size)
{
    int          i;

    if( !buf )
    {
        return ;
    }

    if( prompt )
    {
        printf("%-32s ", prompt);
    }

    for(i=0; i<size; i++)
    {
        printf("%02X ", buf[i]);
    }
    printf("\r\n");

    return ;
}

void dump_buf(const char *prompt, char *buffer, size_t length)
{
    size_t i, j;

    if (prompt)
    {
        printf("%s\n", prompt);
    }

    for (i = 0; i < length; i += 16)
    {
        printf("%08zx: ", i);

        for (j = 0; j < 16; j++)
        {
            if (i + j < length)
            {
                printf("%02x ", buffer[i + j]);
            }
            else
            {
                printf("   ");
            }
        }

        printf(" ");

        for (j = 0; j < 16; j++)
        {
            if (i + j < length)
            {
                unsigned char c = buffer[i + j];
                printf("%c", (c >= 32 && c <= 126) ? c : '.');
            }
            else
            {
                printf(" ");
            }
        }

        printf("\n");
    }
}