The sixth chapter focuses on reusing peripheral driver code. Specifically, this section discusses SPI NOR Flash memory. SPI NOR Flash is a non-volatile flash memory chip that uses an SPI interface. This section uses the MX25L1606 from Wanghong Electronics in Taiwan as an example to demonstrate how similar flash memory can be utilized within AMetal.
### 6.2.1 Basic Functions
The MX25L1606 has a total capacity of 16M bits, which equals 2MB. Each byte corresponds to a unique memory address, resulting in an address range from 0x000000 to 0x1FFFFF. The device organizes memory into blocks, sectors, and pages. A page size is 256 bytes, with each sector containing 16 pages (4KB). Each block contains 16 sectors (64KB). Refer to Table 6.5 for detailed structure.
The communication interface of the MX25L1606 is a standard 4-wire SPI interface, supporting modes 0 and 3. It includes CS, MOSI, MISO, and CLK signals. WP and HOLD pins are used for write protection and data suspension, respectively. These pins are typically not used and can be pulled high via a resistor. The MicroPort-NorFlash module connects to the AM824-Core through the MicroPort interface.
### 6.2.2 Initialization
AMetal provides driver functions for popular SPI Flash devices like the MX25L8006 and MX25L1606. Before using other functionalities, these drivers must be initialized. The function prototype (am_mx25xx.h) is:
```c
am_mx25xx_handle_t am_mx25xx_init(am_mx25xx_dev_t *p_dev, am_mx25xx_devinfo_t *p_devinfo);
```
This function returns the device instance handle. `p_dev` is a pointer to an `am_mx25xx_dev_t` instance, while `p_devinfo` points to `am_mx25xx_devinfo_t` instance information.
An example of defining `am_mx25xx_dev_t` is:
```c
am_mx25xx_dev_t g_mx25xx_dev;
```
Instance information includes the SPI chip select pin, mode, speed, and device model. For the MX25L1606, the SPI mode is set to AM_SPI_MODE_0 or AM_SPI_MODE_3. The chip select pin defaults to PIO0_1 when connected via the MicroPort interface. The SPI speed is set to 86MHz, but it may be limited by the main frequency of the LPC824 chip to 30MHz. The device type is defined using the macro AM_MX25XX_MX25L1606.
If SPI0 is used to communicate with the MX25L1606, the SPI handle is obtained using `am_lpc82x_spi0_inst_init()`:
```c
am_spi_handle_t spi_handle = am_lpc82x_spi0_inst_init();
```
The `spi_handle` is then passed to the initialization function.
### 6.2.3 Interface Function
SPI Flash requires erasing before writing. In addition to read/write functions, there is an erase function. The interface functions are shown in Table 6.6.
Erase resets all data to 0xFF. The smallest unit that can be erased is a sector. The function prototype for erasing an address space is:
```c
int am_mx25xx_erase(am_mx25xx_handle_t handle, uint32_t addr, uint32_t len);
```
The address must be the start of a sector, and the length must be an integer multiple of the sector size. If AM_OK is returned, the erase is successful.
Write operations require the address to have been erased first. The function prototype for writing data is:
```c
int am_mx25xx_write(am_mx25xx_handle_t handle, uint32_t addr, const void *data, uint32_t len);
```
Read operations are performed using:
```c
int am_mx25xx_read(am_mx25xx_handle_t handle, uint32_t addr, void *data, uint32_t len);
```
These functions ensure data is correctly written and read, with appropriate error handling.
### 6.2.4 MTD Universal Interface Function
To make the MX25L1606 independent of specific devices, it is abstracted as an MTD (Memory Technology Device). The MTD interface allows cross-platform calls. The initialization function is:
```c
am_mtd_serv_t *am_mtd_init(am_mx25xx_handle_t mx25xx_handle, am_mtd_serv_t *p_mtd, uint32_t reserved_nblks);
```
The MTD instance handle is obtained, and the reserved blocks are specified. This allows the MTD to manage the device without direct dependency on the specific hardware.
### 6.2.5 FTL Universal Interface Function
FTL (Flash Translation Layer) simplifies programming by abstracting the need for manual erasure. It also extends the lifespan of the Flash by distributing writes across different blocks. The FTL initialization function is:
```c
am_ftl_handle_t am_ftl_init(am_ftl_serv_t *p_ftl, void *p_buf, uint32_t len, am_mtd_serv_t *mtd_handle);
```
This function requires RAM space for internal operations and the MTD handle. FTL operates in fixed-size blocks (512 bytes), allowing efficient data management and reducing wear on the Flash.
### 6.2.6 Micro Database
AMetal implements hash table interfaces based on non-volatile memory, functioning as a micro database. This ensures data persistence even after power loss. The database interface is defined in `hash_kv.h`, with functions such as `hash_kv_init`, `hash_kv_set`, and `hash_kv_get`.
By using non-volatile storage, the database retains data across sessions, making it suitable for applications requiring persistent storage. The hash table structure is adapted to work with files, enabling reliable data management.
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