Booting
14-50 ADSP-21368 SHARC Processor Hardware Reference
From the perspective of the processor, there is no difference between boot-
ing from the three types of SPI slave devices. Since SPI is a full-duplex
protocol, the processor is receiving the same amount of bits that it sends as
a read command. The read command comprises a full 32-bit word (which
is what the processor is initialized to send) comprised of a 24-bit address
with an 8-bit opcode. The 32-bit word that is received while this read
command is transmitted is thrown away in hardware, and can never be
recovered by the user. Because of this, special measures must be taken to
guarantee that the boot stream is identical in all three cases. The processor
boots in least significant bit first (LSBF) format, while most serial memory
devices operate in most significant bit first (MSBF) format. Therefore, it
is necessary to program the device in a fashion that is compatible with the
required LSBF format.
Also, because the processor always transmits 32 bits before it begins read-
ing boot data from the slave device, it is necessary for the VisualDSP++
tools to insert extra data to the boot image (in the loader file) if using
memory devices that do not use the LSBF format. VisualDSP++ has
built-in support for creating a boot stream compatible with both endian
formats and devices requiring 16-bit and 24-bit addresses, as well as those
requiring no read command at all.
Figure 14-16 shows the initial 32-bit word sent out from the processor. As
shown in the figure, the processor initiates the SPI master boot process by
writing an 8-bit opcode (LSB first) to the slave device to specify a read
operation. This read opcode is fixed to 0xC0 (0x03 in MSBF format).
SPIDMAC 0x0000 0007 Enable receive, interrupt on completion
IISPI 0x0008 0000 Start of block 0 normal word memory
IMSPI 0x0000 0001 32-bit data transfers
CSPI 0x0000 0180 0x100 instructions = 0x180 32-bit words
Table 14-14. Parameter Initialization Value for Master Boot (Cont’d)
Parameter Register Initialization Value Comment
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