USB Audio 2.0 Reference Design, XS1-L1 Edition Hardware Manual (1.0)
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5
Optical digital output [D]
An optical digital audio transmitter is used to provide a digital audio output in
IEC60958 consumer mode (S/PDIF) format. The S/PDIF signal is generated from a
1-bit port on the processor as defined in the port map. The data stream from the L1
is reclocked using the external master clock to synchronise the data into the audio
clock domain. This is achieved using a simple external D-type flip-flop.
6
SPI Flash Memory [F]
The board contains a 1Mbit FLASH memory device which is connected via a standard
Serial Peripheral Interface (SPI).
The FLASH is connected to four 1-bit ports as shown in the port map. These are the
standard ports the processor will try to boot from in boot from SPI mode.
Three of these ports are shared with I
2
S digital audio signals therefore the FLASH
cannot be accessed at the same time as digital audio is playing. When accessing the
SPI FLASH, the CODEC is held in reset and it ignores the three inputs shared with SPI
signals. When digital audio is playing, the FLASH is deselected by holding its chip
select (slave select) line inactive. In this mode, the FLASH will ignore other input
signals and set its output high impedance therefore it does not affect the shared
signals. The slave select signal is only active when booting the device therefore and
is held inactive while audio is playing.
The XMOS development tools include the XFLASH utility for programming compiled
programs into the flash memory. Software may also access the FLASH memory at
run-time by interfacing with the above ports. Note that, as mentioned, this can not
happen simultaneously with audio IO.
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