XM014034B datasheet(21/83 Pages) XMOS

21 / 83 page

XU6--QF6A Datasheet

If a large boot image is to be read in, it is faster to rst load a small boot-loader that

reads the large image using a faster SPI clock, for example

MHz or as fast as the

ash device supports.

The pins used for SPI boot are hardcoded in the boot ROM and cannot be changed. If

required, a SPI boot program can be burned into OTP that uses different pins.

The boot sequence up to the start of the SPI boot is outlined in Figure 6

Boot as SPI slave

If set to boot from SPI slave, the processor enables the three pins specied in Figure 8

and expects a boot image to be clocked in. There is no command sequence, data is input

directly from the rst rising edge of clock. The supported clock polarity and phase are

/ and /.

Signal

Description

Slave Select

SCLK

Clock

MOSI

Master Out Slave In (Data)

Figure 8:

SPI slave pins

The xCORE Tile expects each byte to be transferred with the least-signicant bit rst. The

pins used for SPI boot are hardcoded in the boot ROM and cannot be changed. If required,

an SPI boot program can be burned into OTP that uses different pins.

Boot from xConnect Link

If set to boot from an xConnect Link, the processor enables its link(s) shortly after the

boot process starts. Enabling the Link switches off the pull-down resistors on the link,

drives all the TX wires low (the initial state for the Link), and monitors the RX pins for

boot-trafc; they must be low at this stage. If the internal pull-down is too weak to drain

any residual charge, external pull-downs may be required on those pins.

The boot-rom on the core will then:

. Allocate channel-end .

. Input a word on channel-end . It will use this word as a channel to acknowledge the

boot. Provide the null-channel-end xFF

if no acknowledgment is required.

. Input the boot image specied above, including the CRC.

. Input an END control token.

. Output an END control token to the channel-end received in step .

6. Free channel-end .

. Jump to the loaded code.

XM014034B Datasheet(PDF) 21 Page - Xmos Ltd.