Timer
Time scale
HW DMA req every 10 ms
Data
0 ms 10 ms 20 ms 30 ms
3 ms 13 ms 23 ms
Timeout
Counter
WD
pre-load
BC
pre-load
WD
pre-load
BC
pre-load
WD
pre-load
BC
pre-load
WD
pre-load
Note: No timeout interrupt is generated in this example since each block of data patterns are compressed in 3 ms and DMA does
initiate a block transfer every 10 ms.
WD pre-load = watchdog timeout pre-load (CRC_WDTOPLDx)
BC pre-load = block complete timeout pre-load (CRC_BCTOPLDx)
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Module Operation
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SPNU563A–March 2018
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Cyclic Redundancy Check (CRC) Controller Module
18.2.10.4 Underrun Interrupt
Underrun interrupt only occurs in AUTO mode. The interrupt is generated when the CRC Value Register is
not updated with the corresponding signature when the data pattern counter finishes counting. During
AUTO mode, CRC Controller generates DMA request to update CRC Value Register in synchronization to
the corresponding sector of the memory. Signature verification is also performed if underrun condition is
detected. And CRC fail interrupt is generated at the same time as the underrun interrupt.
18.2.10.5 Timeout Interrupt
To ensure that the memory system is examined within a pre-defined time frame and no loss of incoming
data there is a 24 bit timeout counter per CRC channel. The 24 bit timeout down counter can be pre-
loaded with two different pre-load values, watchdog timeout pre-load value (CRC_WDTOPLDx) and block
complete timeout pre-load value (CRC_BCTOPLDx). The timeout counter is clocked by a prescaler clock
which is permanently running at division 64 of HCLK clock.
First pattern of data must be transferred by the DMA before the timeout counter expires, Watchdog
timeout pre-load register (CRC_WDTOPLDx) is used as timeout counter. Block complete timeout pre-load
register (CRC_BCTOPLDx) is used to check if one complete block of data patterns are compressed within
a specific time frame. The timeout counter is first pre-loaded with CRC_WDTOPLDx after either AUTO or
Semi-CPU mode is selected and starts to down count. If the timeout counter expires before DMA transfers
any data pattern to PSA Signature Register then a timeout interrupt is generated. An incoming data
pattern before the timeout counter expires will automatically pre-load the timeout counter with
CRC_BCTOPLDx the block complete timeout pre-load value.
Block complete timeout pre-load value is used to check it one block of data patterns are compressed
within a given time limit. If the timeout counter pre-loaded with CRC_BCTOPLDx value expires before one
block of data patterns are compressed a timeout interrupt is generated. When one block (pattern count x
sector count) of data patterns are compressed before the counter has expired, the counter is pre-loaded
with CRC_WDTOPLDx value again. If the timeout counter is pre-loaded with zero then the counter is
disable and no timeout interrupt is generated.
In Figure 18-6, a timer generates DMA request every 10ms to trigger one block (pattern count x sector
count) transfer. Since we want to make sure that DMA does start to transfer a block every 10 ms we
would set the first pre-load value to 10ms in CRC_WDTOPLDx. We also want to make sure that one block
of data patterns are compressed within 4ms. With such a requirement, we would set the second pre-load
value to 4ms in CRC_BCTOPLDx register.
Figure 18-6. Timeout Example 1
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