SPI Flash 详解
一、序
写这篇文章的目的是今天偶来间看到了 开源库https://github.com/armink/SFUD.git ，遥想起当年入职时的前几个任务就是针对自家的spi flash controller 写一个driver来驱动外置的flash，因为code 固化在rom 中，所以尽量需要兼容不同厂家的flash型号，当时也是折腾了很久。今天有幸看到这份源码，还是满满的回忆。
二. 源码剖析
2.1 初始化
初始化的核心函数在hardware_init中，也体现了识别板载flash型号的核心策略:
首先读取 JEDEC ID，其中包含了manufacturer ID, memory type ID 和flash capacity ID；
然后判断当前flash是否支持SFDP。SFDP标准是JEDEC （固态技术协会）制定的串行 Flash 功能的参数表标准，最新版 V1.6B （[点击这里查看](https://www.jedec.org/standards-documents/docs/jesd216b)）。该标准规定了，每个 Flash 中会存在一个参数表，该表中会存放 Flash 容量、写粒度、擦除命令、地址模式等 Flash 规格参数。目前，除了部分厂家旧款 Flash 型号会不支持该标准，其他绝大多数新出厂的 Flash 均已支持 SFDP 标准。所以该库在初始化时会优先读取 SFDP 表参数。
如果该 Flash 不支持 SFDP 标准，SFUD 会查询配置文件 中提供的 Flash 参数信息表 中是否支持该款 Flash。如果不支持，则可以在配置文件中添加该款 Flash 的参数信息。获取到了 Flash 的规格参数后，就可以实现对 Flash 的全部操作。
/**
* hardware initialize
*/
static sfud_err hardware_init(sfud_flash *flash) {
extern sfud_err sfud_spi_port_init(sfud_flash * flash);
sfud_err result = SFUD_SUCCESS;
size_t i;
result = sfud_spi_port_init(flash);
if (result != SFUD_SUCCESS) {
return result;
}
/* if the user don't configure flash chip information then using SFDP parameter or static flash parameter table */
if (flash->chip.capacity == 0 || flash->chip.write_mode == 0 || flash->chip.erase_gran == 0
|| flash->chip.erase_gran_cmd == 0) {
/* read JEDEC ID include manufacturer ID, memory type ID and flash capacity ID */
result = read_jedec_id(flash);
if (result != SFUD_SUCCESS) {
return result;
}
#ifdef SFUD_USING_SFDP
extern bool sfud_read_sfdp(sfud_flash *flash);
/* read SFDP parameters */
if (sfud_read_sfdp(flash)) {
flash->chip.name = NULL;
flash->chip.capacity = flash->sfdp.capacity;
/* only 1 byte or 256 bytes write mode for SFDP */
if (flash->sfdp.write_gran == 1) {
flash->chip.write_mode = SFUD_WM_BYTE;
} else {
flash->chip.write_mode = SFUD_WM_PAGE_256B;
}
/* find the the smallest erase sector size for eraser. then will use this size for erase granularity */
flash->chip.erase_gran = flash->sfdp.eraser[0].size;
flash->chip.erase_gran_cmd = flash->sfdp.eraser[0].cmd;
for (i = 1; i < SFUD_SFDP_ERASE_TYPE_MAX_NUM; i++) {
if (flash->sfdp.eraser[i].size != 0 && flash->chip.erase_gran > flash->sfdp.eraser[i].size) {
flash->chip.erase_gran = flash->sfdp.eraser[i].size;
flash->chip.erase_gran_cmd = flash->sfdp.eraser[i].cmd;
}
}
} else {
#endif
#ifdef SFUD_USING_FLASH_INFO_TABLE
/* read SFDP parameters failed then using SFUD library provided static parameter */
for (i = 0; i < sizeof(flash_chip_table) / sizeof(sfud_flash_chip); i++) {
if ((flash_chip_table[i].mf_id == flash->chip.mf_id)
&& (flash_chip_table[i].type_id == flash->chip.type_id)
&& (flash_chip_table[i].capacity_id == flash->chip.capacity_id)) {
flash->chip.name = flash_chip_table[i].name;
flash->chip.capacity = flash_chip_table[i].capacity;
flash->chip.write_mode = flash_chip_table[i].write_mode;
flash->chip.erase_gran = flash_chip_table[i].erase_gran;
flash->chip.erase_gran_cmd = flash_chip_table[i].erase_gran_cmd;
break;
}
}
#endif
#ifdef SFUD_USING_SFDP
}
#endif
}
/* reset flash device */
result = reset(flash);
if (result != SFUD_SUCCESS) {
return result;
}
/* if the flash is large than 16MB (256Mb) then enter in 4-Byte addressing mode */
if (flash->chip.capacity > (1L << 24)) {
result = set_4_byte_address_mode(flash, true);
} else {
flash->addr_in_4_byte = false;
}
return result;
}另外为了方便移植，SFUD把与平台spi falsh controller相关的函数封装在结构体sfud_flash中的sfud_spi中，由平台移植者负责填充相应的结构体，体现了面向对象的编程方法。
/**
* SPI device
*/
typedef struct __sfud_spi {
/* SPI device name */
char *name;
/* SPI bus write read data function */
sfud_err (*wr)(const struct __sfud_spi *spi, const uint8_t *write_buf, size_t write_size, uint8_t *read_buf,
size_t read_size);
#ifdef SFUD_USING_QSPI
/* QSPI fast read function */
sfud_err (*qspi_read)(const struct __sfud_spi *spi, uint32_t addr, sfud_qspi_read_cmd_format *qspi_read_cmd_format,
uint8_t *read_buf, size_t read_size);
#endif
/* lock SPI bus */
void (*lock)(const struct __sfud_spi *spi);
/* unlock SPI bus */
void (*unlock)(const struct __sfud_spi *spi);
/* some user data */
void *user_data;
} sfud_spi, *sfud_spi_t;
sfud_err sfud_spi_port_init(sfud_flash *flash) {
sfud_err result = SFUD_SUCCESS;
/**
* add your port spi bus and device object initialize code like this:
* 1. rcc initialize
* 2. gpio initialize
* 3. spi device initialize
* 4. flash->spi and flash->retry item initialize
* flash->spi.wr = spi_write_read; //Required
* flash->spi.qspi_read = qspi_read; //Required when QSPI mode enable
* flash->spi.lock = spi_lock;
* flash->spi.unlock = spi_unlock;
* flash->spi.user_data = &spix;
* flash->retry.delay = null;
* flash->retry.times = 10000; //Required
*/
return result;
}2.2 erase 操作
因为spi flash 本身的特性（只能从1->0的变化），在执行写操作之前，需要进行erase动作。
但由于不同的flash 可能支持不同的擦除命令和对应的擦除块大小，所以erase操作的核心就是选择合适的擦除命令来执行操作操作。
erase 操作的flow如下：
1.参数检测，包括参数错误检测和片擦除操作是否满足；
2.lock flash
3.设置flash write enable
4.如果支持SFDP，寻找最优的擦除命令来加快擦除操作，并以while loop的方式进行擦除
5.disable & unlock
/**
* erase flash data
*
* @note It will erase align by erase granularity.
*
* @param flash flash device
* @param addr start address
* @param size erase size
*
* @return result
*/
sfud_err sfud_erase(const sfud_flash *flash, uint32_t addr, size_t size) {
/* check the flash address bound */
if (addr + size > flash->chip.capacity) {
SFUD_INFO("Error: Flash address is out of bound.");
return SFUD_ERR_ADDR_OUT_OF_BOUND;
}
if (addr == 0 && size == flash->chip.capacity) {
return sfud_chip_erase(flash);
}
/* lock SPI */
if (spi->lock) {
spi->lock(spi);
}
/* loop erase operate. erase unit is erase granularity */
while (size) {
/* if this flash is support SFDP parameter, then used SFDP parameter supplies eraser */
#ifdef SFUD_USING_SFDP
size_t eraser_index;
if (flash->sfdp.available) {
/* get the suitable eraser for erase process from SFDP parameter */
eraser_index = sfud_sfdp_get_suitable_eraser(flash, addr, size);
cur_erase_cmd = flash->sfdp.eraser[eraser_index].cmd;
cur_erase_size = flash->sfdp.eraser[eraser_index].size;
} else {
#else
{
#endif
cur_erase_cmd = flash->chip.erase_gran_cmd;
cur_erase_size = flash->chip.erase_gran;
}
/* set the flash write enable */
result = set_write_enabled(flash, true);
if (result != SFUD_SUCCESS) {
goto __exit;
}
cmd_data[0] = cur_erase_cmd;
make_adress_byte_array(flash, addr, &cmd_data[1]);
cmd_size = flash->addr_in_4_byte ? 5 : 4;
result = spi->wr(spi, cmd_data, cmd_size, NULL, 0);
if (result != SFUD_SUCCESS) {
SFUD_INFO("Error: Flash erase SPI communicate error.");
goto __exit;
}
result = wait_busy(flash);
if (result != SFUD_SUCCESS) {
goto __exit;
}
/* make erase align and calculate next erase address */
if (addr % cur_erase_size != 0) {
if (size > cur_erase_size - (addr % cur_erase_size)) {
size -= cur_erase_size - (addr % cur_erase_size);
addr += cur_erase_size - (addr % cur_erase_size);
} else {
goto __exit;
}
} else {
if (size > cur_erase_size) {
size -= cur_erase_size;
addr += cur_erase_size;
} else {
goto __exit;
}
}
}
__exit:
/* set the flash write disable */
set_write_enabled(flash, false);
/* unlock SPI */
if (spi->unlock) {
spi->unlock(spi);
}
return result;
}2.3 write 操作
跟erase 操作类似，在write之前需要设置write enable & lock 动作， 同时因为write page 操作是256 bytes为单位的，如果连续写入超过256bytes，会wrap around 到 该page byte 0的位置，所以page256_or_1_byte_write function的核心就是以page 对齐的一page一page的写入。
/*API*/
/**
* write flash data (no erase operate)
*
* @param flash flash device
* @param addr start address
* @param size write size
* @param data write data
*
* @return result
*/
sfud_err sfud_write(const sfud_flash *flash, uint32_t addr, size_t size, const uint8_t *data) {
sfud_err result = SFUD_SUCCESS;
if (flash->chip.write_mode & SFUD_WM_PAGE_256B) {
result = page256_or_1_byte_write(flash, addr, size, 256, data);
} else if (flash->chip.write_mode & SFUD_WM_AAI) {
result = aai_write(flash, addr, size, data);
} else if (flash->chip.write_mode & SFUD_WM_DUAL_BUFFER) {
//TODO dual-buffer write mode
}
return result;
}
/*Internal Function*/
/**
* write flash data (no erase operate) for write 1 to 256 bytes per page mode or byte write mode
*
* @param flash flash device
* @param addr start address
* @param size write size
* @param write_gran write granularity bytes, only support 1 or 256
* @param data write data
*
* @return result
*/
static sfud_err page256_or_1_byte_write(const sfud_flash *flash, uint32_t addr, size_t size, uint16_t write_gran,
const uint8_t *data) {
/* check the flash address bound */
if (addr + size > flash->chip.capacity) {
SFUD_INFO("Error: Flash address is out of bound.");
return SFUD_ERR_ADDR_OUT_OF_BOUND;
}
/* lock SPI */
if (spi->lock) {
spi->lock(spi);
}
/* loop write operate. write unit is write granularity */
while (size) {
/* set the flash write enable */
result = set_write_enabled(flash, true);
if (result != SFUD_SUCCESS) {
goto __exit;
}
cmd_data[0] = SFUD_CMD_PAGE_PROGRAM;
make_adress_byte_array(flash, addr, &cmd_data[1]);
cmd_size = flash->addr_in_4_byte ? 5 : 4;
/* make write align and calculate next write address */
if (addr % write_gran != 0) {
if (size > write_gran - (addr % write_gran)) {
data_size = write_gran - (addr % write_gran);
} else {
data_size = size;
}
} else {
if (size > write_gran) {
data_size = write_gran;
} else {
data_size = size;
}
}
size -= data_size;
addr += data_size;
memcpy(&cmd_data[cmd_size], data, data_size);
result = spi->wr(spi, cmd_data, cmd_size + data_size, NULL, 0);
if (result != SFUD_SUCCESS) {
SFUD_INFO("Error: Flash write SPI communicate error.");
goto __exit;
}
result = wait_busy(flash);
if (result != SFUD_SUCCESS) {
goto __exit;
}
data += data_size;
}
__exit:
/* set the flash write disable */
set_write_enabled(flash, false);
/* unlock SPI */
if (spi->unlock) {
spi->unlock(spi);
}
return result;
}2.4 read 操作
read 操作则相对简明一些，不表。
/**
* read flash data
*
* @param flash flash device
* @param addr start address
* @param size read size
* @param data read data pointer
*
* @return result
*/
sfud_err sfud_read(const sfud_flash *flash, uint32_t addr, size_t size, uint8_t *data) {
...
/* check the flash address bound */
if (addr + size > flash->chip.capacity) {
SFUD_INFO("Error: Flash address is out of bound.");
return SFUD_ERR_ADDR_OUT_OF_BOUND;
}
/* lock SPI */
if (spi->lock) {
spi->lock(spi);
}
result = wait_busy(flash);
if (result == SFUD_SUCCESS) {
#ifdef SFUD_USING_QSPI
if (flash->read_cmd_format.instruction != SFUD_CMD_READ_DATA) {
result = spi->qspi_read(spi, addr, (sfud_qspi_read_cmd_format *)&flash->read_cmd_format, data, size);
} else
#endif
{
cmd_data[0] = SFUD_CMD_READ_DATA;
make_adress_byte_array(flash, addr, &cmd_data[1]);
cmd_size = flash->addr_in_4_byte ? 5 : 4;
result = spi->wr(spi, cmd_data, cmd_size, data, size);
}
}
/* unlock SPI */
if (spi->unlock) {
spi->unlock(spi);
}
return result;
}
3.使用方式与移植
见开源库ReadME
4.总结
对于无OS系统或者微内核的系统而言，该开源库确实值得在工程中使用，因为它考虑了兼容不同的flash，针对不同的flash 的特性又有针对性的读写优化操作。在已支持的flash list 中，使用者可以屏蔽了解flash 的底层特性和各种不同的命令。