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GR716-DS-UM, May 2019, Version 1.29
449
www.cobham.com/gaisler
GR716
The final four bits of the command token consist of a checksum for all the previous command token
bits transmitted in this message. The CRC-4 should be computed for the following 28 bits, Command
word #1 (16bits, MSB first sent to the CRC generator) and Command word #2 (excluding this CRC-4
field) (12bits, MSB first sent to the CRC generator). The Prefix and Spare fields are included in the
CRC calculation. The generator polynomial used is X4 + X + 1. In this SPI slave receiving end the
CRC-4 is calculated internally for the received command token, if the calculated CRC-4 does not
match the expected value (this field) the corresponding command token is discarded and message
error status is enabled and transmitted to master as part of the next response token.
Payload data
The payload consist of the data need to be transferred from the master to slave. Depending on the
command executed the master must include valid data or dummy information in the form of string of
zeros. For example the write command have the data to be written as the payload but the read com-
mand have dummy information in the form of string of zeros.
Payload CRC
When a valid payload is delivered in the payload data section of the message a Payload CRC (CRC-
16) must be included at the end of the message. The generator polynomial used is x16+ x15+ x2+ 1.
When dummy information in the form of string of zeros is included then no Payload CRC need to be
attached then the payload CRC field must be all zero (0X0000). In the SPI slave receiving end the
CRC-16 is calculated internally for the received payload data, if the calculated CRC-16 does not
match the expected value (this field) the corresponding operation with respect to the command is not
performed and message error status is enabled and transmitted to master as part of the next response
token.
45.6.1 Command Code
The command code specify the operating instruction for the receiving slave. The detailed explanation
of each command code and its implementation are explained in the table below.
The RESET_SPI command resets the SPI slave device to a power up initialized state. The SPI slave
resets the system only if it received a valid command. If the prefix and spare bits does not match or if
the calculated CRC-4 does not match the expected value then the RESET_SPI command is discarded.
Time synchronization command
Table 598.
Reset Command
Code
Command
Length
Sub-
Address
Payload
Description
0x00
RESET_SPI
0x00
0x00
None
This command will reset all the spi slave
device registers to the default value except
the time registers (TIME1, TIME2) and core
enable registers (ENN and ENR)