Ultra Dma Crc Rules - Fujitsu MPA3017AT Product Manual

13) The host shall neither negate STOP nor HSTROBE until at least t
DMACK-.
14) The host shall not assert DIOW-, CS0-, CS1-, DA2, DA1, or DA0 until at least t
negating DMACK.
5.5.5

Ultra DMA CRC rules

The following is a list of rules for calculating CRC, determining if a CRC error has occurred
during an Ultra DMA burst, and reporting any error that occurs at the end of a command.
a) Both the host and the device shall have a 16-bit CRC calculation function.
b) Both the host and the device shall calculate a CRC value for each Ultra DMA burst.
c) The CRC function in the host and the device shall be initialized with a seed of 4ABAh at the
beginning of an Ultra DMA burst before any data is transferred.
d) For each STROBE transition used for data transfer, both the host and the device shall calculate
a new CRC value by applying the CRC polynomial to the current value of their individual
CRC functions and the word being transferred. CRC is not calculated for the return of
STROBE to the asserted state after the Ultra DMA burst termination request has been
acknowledged.
e) At the end of any Ultra DMA burst the host shall send the results of its CRC calculation
function to the device on DD (15:0) with the negation of DMACK-.
f) The device shall then compare the CRC data from the host with the calculated value in its own
CRC calculation function. If the two values do not match, the device shall save the error and
report it at the end of the command. A subsequent Ultra DMA burst for the same command
that does not have a CRC error shall not clear an error saved from a previous Ultra DMa burst
in the same command. If a miscompare error occurs during one or more Ultra DMA bursts for
any one command, at the end of the command, the device shall report the first error that
occurred.
g) For READ DMA or WRITE DMA commands: When a CRC error is detected, it shall be
reported by setting both ICRC and ABRT (bit 7 and bit 2 in the Error register) to one. ICRC is
defined as the "Interface CRC Error" bit. The host shall respond to this error by re-issuing the
command.
h) A host may send extra data words on the last Ultra DMA burst of a data out command. If a
device determines that all data has been transferred for a command, the device shall terminate
the burst. A device may have already received more data words than were required for the
command. These extra words are used by both the host and the device to calculate the CRC,
but, on an Ultra DMA data out burst, the extra words shall be discarded by the device.
I) The CRC generator polynomial is : G (X) = X16 + X12 + X5 + 1.
Note: Since no bit clock is available, the recommended approach for calculating CRC is to use
a word clock derived from the bus strobe. The combinational logic shall then be equivalent to
shifting sixteen bits serially through the generator polynominal where DD0 is shifted in first
and DD15 is shifted in last.
C141-E034-02EN
after negating
ACK
after
ACK
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