
Quad-SPI interface (QUADSPI)
RM0351
480/1830
DocID024597 Rev 5
FIFO and data management
In indirect mode, data go through a 16-byte FIFO which is internal to the QUADSPI.
FLEVEL[4:0] (QUADSPI_SR[12:8]) indicates how many bytes are currently being held in
the FIFO.
In indirect write mode (FMODE = 00), firmware adds data to the FIFO when it writes
QUADSPI_DR. Word writes add 4 bytes to the FIFO, halfword writes add 2 bytes, and byte
writes add only 1 byte. If firmware adds too many bytes to the FIFO (more than is indicated
by DL[31:0]), the extra bytes are flushed from the FIFO at the end of the write operation
(when TCF is set).
Byte/halfword accesses to QUADSPI_DR must be done only to the least significant
byte/halfword of the 32-bit register.
FTHRES[3:0] is used to define a FIFO threshold. When the threshold is reached, the FTF
(FIFO threshold flag) is set. In indirect read mode, FTF is set when the number of valid
bytes to be read from the FIFO is above the threshold. FTF is also set if there are data in the
FIFO after the last byte is read from the Flash memory, regardless of the FTHRES setting.
In indirect write mode, FTF is set when the number of empty bytes in the FIFO is above the
threshold.
If FTIE = 1, there is an interrupt when FTF is set. If DMAEN = 1, a DMA transfer is initiated
when FTF is set. FTF is cleared by HW as soon as the threshold condition is no longer true
(after enough data has been transferred by the CPU or DMA).
In indirect read mode when the FIFO becomes full, the QUADSPI temporarily stops reading
bytes from the Flash memory to avoid an overrun. Please note that the reading of the Flash
memory does not restart until 4 bytes become vacant in the FIFO (when FLEVEL
≤
11).
Thus, when FTHRES
≥
13, the application must take care to read enough bytes to assure
that the QUADSPI starts retrieving data from the Flash memory again. Otherwise, the FTF
flag stays at '0' as long as 11 < FLEVEL < FTHRES.
17.4.6
QUADSPI status flag polling mode
In automatic-polling mode, the QUADSPI periodically starts a command to read a defined
number of status bytes (up to 4). The received bytes can be masked to isolate some status
bits and an interrupt can be generated when the selected bits have a defined value.
The accesses to the Flash memory begin in the same way as in indirect read mode: if no
address is required (AMODE = 00), accesses begin as soon as the QUADSPI_CCR is
written. Otherwise, if an address is required, the first access begins when QUADSPI_AR is
written. BUSY goes high at this point and stays high even between the periodic accesses.
The contents of MASK[31:0] (QUADSPI_PSMAR) are used to mask the data from the Flash
memory in automatic-polling mode. If the MASK[n] = 0, then bit n of the result is masked
and not considered. If MASK[n] = 1, and the content of bit[n] is the same as MATCH[n]
(QUADSPI_PSMAR), then there is a match for bit n.
If the polling match mode bit (PMM, QUADSPI_CR[23]) is 0, then “AND” match mode is
activated. This means status match flag (SMF) is set only when there is a match on all of the
unmasked bits.
If PMM = 1, then “OR” match mode is activated. This means SMF is set if there is a match
on any of the unmasked bits.
An interrupt is called when SMF is set if SMIE = 1.