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QuadSPI

Implementing QSPI enables Mbed OS to communicate with external memories much faster than via SPI. Because the communication can be up to four lines between the host and a device.

The most common use case is an external memory to use as additional data storage.

Assumptions

Defined behavior

  • A target implementation covers most of the QSPI frame format (some targets might not provide the flexibility for setting all frame parameters).
  • Command transfer - A target might provide additional functions for sending device-specific commands. If it does not, you can implement it using read and write functions. (This is target or driver dependent.)

Undefined behavior

  • Calling any function other than qspi_init before the initialization of the QSPI.

Dependency

QSPI peripheral

Implementing QuadSPI

The target needs to define the qspi_s structure - target specific QSPI object.

Functions to implement:

qspi_status_t qspi_init(qspi_t *obj, PinName io0, PinName io1, PinName io2, PinName io3, PinName sclk, PinName ssel, uint32_t hz, uint8_t mode);
qspi_status_t qspi_free(qspi_t *obj);
qspi_status_t qspi_frequency(qspi_t *obj, int hz);
qspi_status_t qspi_write(qspi_t *obj, const qspi_command_t *command, const void *data, size_t *length);
qspi_status_t qspi_command_transfer(qspi_t *obj, const qspi_command_t *command, const void *tx_data, size_t tx_size, void *rx_data, size_t rx_size);
qspi_status_t qspi_read(qspi_t *obj, const qspi_command_t *command, void *data, size_t *length);

Use qspi_write and qspi_read for data transfers. For communicating with a device, use qspi_command_transfer.

To enable the QSPI HAL, define QSPI in the targets.json file inside device_has:

"TARGET_NAME": {
   "device_has": ["QSPI"]
}

Testing

To be implemented

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