Csr Accesses - Motorola MVME2600 Series Reference Manual

Functional Description

CSR Accesses

An important part of the operation of a Falcon pair is that the value written
to the internal control registers and SRAM in each of the two chips must
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be the same at all times. In order to facilitate this, writes to the pair itself
are restricted to the upper Falcon only. When software writes to the upper
Falcon, hardware in the two chips shifts this same value into the lower
Falcon before the cycle completion is acknowledged. The shifting is done
in holding registers such that the actual update of the control register
happens on the same CLOCK cycle in both chips. Writes to the upper
Falcon can be single-byte or 4-byte. Writes to the lower Falcon are
ignored.
This duplicating of writes from upper to lower applies to the Falcon's
internal registers and SRAM only. No duplication is performed for writes
to DRAM, ROM/Flash, or the External Register set.
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