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Clarify that cache is flushed, but that function is intended for low-level metadata access during startup (#322)

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Luke Wren 2021-04-09 14:05:29 +01:00 committed by GitHub
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1 changed files with 15 additions and 5 deletions
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src/rp2_common/hardware_flash/include/hardware/flash.h
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@ -83,14 +83,24 @@ void flash_get_unique_id(uint8_t *id_out);
/*! \brief Execute bidirectional flash command /*! \brief Execute bidirectional flash command
* \ingroup hardware_flash * \ingroup hardware_flash
* *
* Execute a bidirectional command to the flash. Bytes are simultaneously * Low-level function to execute a serial command on a flash device attached
* transmitted and received. Therefore, both buffers must be the same length, * to the QSPI interface. Bytes are simultaneously transmitted and received
* from txbuf and to rxbuf. Therefore, both buffers must be the same length,
* count, which is the length of the overall transaction. This is useful for * count, which is the length of the overall transaction. This is useful for
* reading metadata from the flash chip. Do *NOT* use it to mutate the data * reading metadata from the flash chip, such as device ID or SFDP
* stored on the flash because it will not flush the cache. * parameters.
*
* The XIP cache is flushed following each command, in case flash state
* has been modified. Like other hardware_flash functions, the flash is not
* accessible for execute-in-place transfers whilst the command is in
* progress, so entering a flash-resident interrupt handler or executing flash
* code on the second core concurrently will be fatal. To avoid these pitfalls
* it is recommended that this function only be used to extract flash metadata
* during startup, before the main application begins to run: see the
* implementation of pico_get_unique_id() for an example of this.
* *
* \param txbuf Pointer to a byte buffer which will be transmitted to the flash * \param txbuf Pointer to a byte buffer which will be transmitted to the flash
* \param rxbuf Pointer to a byte buffer where data received from the flash will be written * \param rxbuf Pointer to a byte buffer where data received from the flash will be written. txbuf and rxbuf may be the same buffer.
* \param count Length in bytes of txbuf and of rxbuf * \param count Length in bytes of txbuf and of rxbuf
*/ */
void flash_do_cmd(const uint8_t *txbuf, uint8_t *rxbuf, size_t count); void flash_do_cmd(const uint8_t *txbuf, uint8_t *rxbuf, size_t count);