SMART Embedded Computing MVME2502, Installation And User Manual

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84 MVME2502 Installation and Use (6806800R96L)
Functional Description
Functional Description
The MVME2502 CPLD controls the chip select to SPI devices A and B. The CPLD chip
select control is based on the Switch Bank (S2-2).
On power-up, the selection of the SPI boot device is strictly based upon the Switch Bank
(S2-2) setting. Depending on the S2-2 setting, SPI_SEL0 is routed to one of two SPI
devices. The selected SPI device must contain a boot image. Once the boot image is
copied into memory and executed, the CPLD will wait, and once the P2020 will write on one
bit of the CPLD watchdog register, the CPLD will then pass through the SPI chip select from
the P2020 to SPI device chip selects. Now the software can perform read/write processes
on any SPI device, including copying from one SPI device to another.
With this flexible approach to firmware redundancy, one should always be able to recover
from a corrupt active firmware image, as long as a healthy firmware image is maintained in
single bootable SPI Device.
The MVME2502 supports automatic switch over. If booting one device is not successful,
the watchdog will trigger the board reset and it will automatically boot on the other device.
4.6.4 Crisis Recovery
The MVME2502 provides an independent boot firmware recovery mechanism for the
operating system. The firmware recovery can be performed without leaving the firmware
environment.
During crisis recovery, the healthy boot image contained in SPI Device B is copied to SPI
Device A, replacing the corrupt boot image contained in SPI Device A.
Figure 4-2 SPI Device Multiplexing Logic