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Serial Boot Facility (SBF)
Freescale Semiconductor
12-7
12.5.2
FAST_READ Feature Initialization
Many SPI flash memories implement a FAST_READ command that allows for a substantially higher
shift-clock frequency. The SBF always uses the normal read command when coming out of a
power-on/hard reset. However, when coming out of a soft reset, it is possible to use FAST_READ because
the SBF machine state is not lost.
For this reason, the SBFCR[FR] sticky bit may be set, causing the FAST_READ command to be issued
instead of the read command in the event of a soft reset. To enable the FAST_READ feature, set
SBFCR[FR] in the same write that sets the SBFCR[BLDIV] field. The value written to SBFCR[BLDIV]
should correspond to the frequency the SPI memory supports in FAST_READ mode. After a soft reset,
...
...
0x12 + 4
(BLL + 1)
CODE_BYTE_[4
(BLL + 1) - 1]
1
This assumes SBFSR[PLL] is non-zero. If PLL is zero, the SBF
does not access data at these addresses.
2
Start of user code copied into the on-chip SRAM.
CODE_BYTE_0–3 is the supervisor stack pointer (SP) when
loading completes. CODE_BYTE_4–7 is the program counter
(PC) when loading completes.
Table 12-6. SPI Memory Organization (256-pin Devices)
Byte Address
Data Contents
0x0
{0000,BLDIV[3:0]}
0x1
BLL[7:0]
0x2
BLL[15:8]
0x3
0x00
0x4
0x00
0x5
RCON[119:112]
0x6
RCON[127:120]
0x7
1
1
This assumes SBFSR[BLL] is non-zero. If BLL is zero, the SBF
does not access data at these addresses.
CODE_BYTE_0
2
2
Start of user code copied into the on-chip SRAM.
CODE_BYTE_0–3 is the supervisor stack pointer (SP) when
loading completes. CODE_BYTE_4–7 is the program counter
(PC) when loading completes.
0x8
CODE_BYTE_1
...
...
0x6 + 4
(BLL + 1)
CODE_BYTE_[4
(BLL + 1) - 1]
Table 12-5. SPI Memory Organization (360-pin Devices) (continued)
Byte Address
Data Contents
Содержание MCF54455
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