MOTOROLA
OnCE™ DEBUG MODULE
MMC2001
16-20
REFERENCE MANUAL
16.12 Instruction Address FIFO Buffer (PC FIFO)
To ease debugging activity and keep track of program flow, a first-in-first-out (FIFO)
buffer stores the addresses of the last eight instruction change-of-flow prefetches that
were issued.
The FIFO is implemented as a circular buffer containing eight 32-bit registers and one
3-bit counter. All the registers have the same address, but any read access to the
FIFO address causes the counter to increment and point to the next FIFO register.
The registers are serially available to the external command controller through the
common FIFO address. Figure 16-11 shows the block diagram of the PC FIFO.
Figure 16-11 OnCE PC FIFO
PC FIFO Register 0
TDO
TCK
PC FIFO Register 1
PC FIFO Register 2
PC FIFO Register 3
PC FIFO Register 4
Instruction Fetch Address
Circular
Buffer
Pointer
PC FIFO Shift Register
PC FIFO Register 5
PC FIFO Register 6
PC FIFO Register 7
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