RM0319 datasheet(96/368 Pages) STMICROELECTRONICS

96 / 368 page

Serial NOR Flash controller (SMI)

RM0319

96/368

Doc ID 022640 Rev 3

In both operation modes, SMI can work:

●

In normal mode, by clearing the FAST bit in the SMI_CR1 register, with a frequency up

to 20 MHz (19 MHz at power-on).

●

In fast mode, by setting the FAST bit in the SMI_CR1 register, with a frequency ranging

from 20 MHz to 50 MHz.

Hardware mode

Hardware mode allows SMI to perform read/write requests from any AHB master which can

directly access the external serial memory.

In particular, external serial memory is mapped in AHB address space as shown in

Figure 22,

Figure 22.

External SPI memory map in AHB address space

In this mode, both the transmit register SMI_TR and the receive register SMI_RR must not

be accessed. They are actually in charge of the SMI state machine to communicate with the

selected external memory device, whenever an AHB master reads or writes an address into

the memory.

At power-on reset, the SMI operates in hardware mode (allowing to boot from external

memory, as explained in Section 7.5.1).

Software mode

Software mode is intended to allow any AHB master to access external serial memory by

programming the internal SMI registers and reading them for memory replies. In this mode,

a direct transfer to/from external memory – that is, bypassing SMI registers - is not permitted

to an AHB master.

In particular, software mode is used both to transfer any data or commands from transmit

(SMI_RR). The transfer actually starts setting the dedicated SEND bit in the SMI_CR2

Besides, in software mode the application code being executed by the CPU cannot be

fetched from external memory, because of the incompatibility between software and

hardware mode. The code must be either hosted by internal memory or previously loaded

from external memory while SMI is in hardware mode.

For example, software mode is used to erase Flash memories before writing. Indeed,

memory erasing cannot be performed in hardware mode due to the incompatibility of Flash

devices from different vendors.

External Serial

Memory Space

CS0

CS1

0xF9FF_FFFF

0xF800_0000

0xF9FF_FFFF

0xF800_0000

0xF900_0000

0xF8FF_FFFF

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