ADSP-21368 SHARC Processor Hardware Reference 14-47
System Design
The initial boot of the 256-word loader kernel requires an 8-bit host to
transmit 1536 8-bit words. The SPI DMA count value of 0x180 is equal
to 384 words. Since one 32-bit word is created from four packed 8-bit
words, the total number of 8-bit words transmitted is 1536.
For all boot modes, the VisualDSP++ loader automatically outputs the
correct word width and count based on the project settings. For more
information, see the VisualDSP++ tools documentation.
Slave Boot Mode
In slave boot mode, the host processor initiates the booting operation by
activating the
SPICLK signal and asserting the SPIDS signal to the active
low state. The 256-word kernel is loaded 32 bits at a time, through the
SPI receive shift register (RXSR). To receive 256 instructions (48-bit
words) properly, the SPI DMA initially loads a DMA count of 0x180
(384) 32-bit words, which is equivalent to 0x100 (256) 48-bit words.
L
The processor’s SPIDS pin should not be tied low. When in SPI
slave mode, including booting, the SPIDS signal is required to tran-
sition from high to low. SPI slave booting uses the default bit
settings shown in Table 14-11.
SPI word 9 = 0xBB
SPI word 10 = 0xAA
SPI word 11 = 0x88
SPI word 12 = 0x77
Table 14-11. SPI Slave Boot Bit Settings
Bit Setting Comment
SPIEN Set (= 1) SPI enabled
SPIMS Cleared (= 0) Slave device
MSBF Cleared (= 0) LSB first
WL 10, 32-bit SPI Receive shift register word length
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