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Chapter 5: Plugging into a Target System
Configuring the Emulator for In-Circuit Operation
Step 7. If you use the 68302 built-in DRAM refresh
The 68302 has a special built-in function that allows for automatic refresh of
DRAM with no additional target hardware. If your target system does not rely on
this built-in feature of the 68302, you can skip this step. If you do use the built-in
DRAM refresh feature, you must use the foreground monitor; otherwise, DRAM
values will become corrupted when you break into the background monitor.
In order to make the DRAM refresh work, you should follow the steps outlined in
"Step 6. Set up the emulator for the foreground monitor". You will need to make
one addition to the foreground monitor source code to ensure that DRAM refreshes
occur properly while in the monitor. To make the addition, edit the monitor source
and find the following section:
TARG_MEM_WR
Then, add the next two lines immediately after the BPL instruction:
Why is this needed? Whenever a break into the monitor occurs, the emulator
always checks the value in the BAR and rewrites it. Without this addition, the
emulator will make two separate byte accesses to locations 0F2H and 0F3H. If a
DRAM refresh occurs in between the write to 0F2H and 0F3H, the DRAM refresh
operation will not function properly. Making this change ensures that a DRAM
refresh will not occur during a write to the BAR.
After making this change, you should reassemble and relink the monitor; then,
reload your configuration.
166
MOVE.L
TARG_START,A0
MOVE.L
#XFR_BUF,A1
MOVE.W
TARG_BYTES,A2
CMP.W
#00800H,A2
BPL
TARG_WORD_WR
CMPA.L
#$F2,A0
BEQ
TARG_WORD_WR
; If write to 0F2H, force a word write
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