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Chapter 28 Debug module (DBG)
28.4.5 FIFO
The FIFO is an eight word deep FIFO. In all trigger modes except for event only, the data
stored in the FIFO will be change of flow addresses. In the event only trigger modes only
the data bus value corresponding to the event is stored. In event only trigger modes, the
high byte of the valid data from the FIFO will always read a 0x00.
28.4.5.1 Storing data in FIFO
In all trigger modes except for the event only modes, the address stored in the FIFO will
be determined by the change of flow indicators from the core. The signal core_cof[1]
indicates the current core address is the destination address of an indirect JSR or JMP
instruction, or a RTS or RTI instruction or interrupt vector and the destination address
should be stored. The signal core_cof[0] indicates that a conditional branch was taken
and that the source address of the conditional branch should be stored.
28.4.5.2 Storing with begin-trigger
Storing with begin-trigger can be used in all trigger modes. Once the DBG module is
enabled and armed in the begin-trigger mode, data is not stored in the FIFO until the
trigger condition is met. Once the trigger condition is met the DBG module will remain
armed until 8 words are stored in the FIFO. If the core_cof[1] signal becomes asserted,
the current address is stored in the FIFO. If the core_cof[0] signal becomes asserted, the
address registered during the previous last cycle is decremented by two and stored in the
FIFO.
28.4.5.3 Storing with end-trigger
Storing with end-trigger cannot be used in event-only trigger modes. After the DBG
module is enabled and armed in the end-trigger mode, data is stored in the FIFO until the
trigger condition is met. If the core_cof[1] signal becomes asserted, the current address is
stored in the FIFO. If the core_cof[0] signal becomes asserted, the address registered
during the previous last cycle is decremented by two and stored in the FIFO. When the
trigger condition is met, the DBG_C[ARM] and DBG_S[ARMF] will be cleared and no
more data will be stored. In non-event only end-trigger modes, if the trigger is at a change
of flow address the trigger event will be stored in the FIFO.
MC9S08SU16 Reference Manual, Rev. 5, 4/2017
NXP Semiconductors
573
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