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RISC Graphics Processor
11-4
MC68322 USER’S MANUAL
MOTOROLA
The RGP can detect certain errors during the execution of a display list, including an
out-of-range display list start address, out-of-range graphic order operand addresses, and
illegal graphic order opcodes. When the RGP detects one of these errors, it immediately
stops processing the current display list and sets the RIER’s RER bit. When RER is set, the
RDR determines the graphic order that generated the error. However, the RGP must be
reset by an RGP soft-reset to return it to normal operation. A write to the RGP bit in the soft-
reset register initiates an RGP soft-reset operation. See Section 5 Interrupt and Exception
Handling for more information. On an RGP soft-reset, the RGP registers are initialized as
follows:
1. RSR is purged.
2. RIER’s DLF and RBY bits are cleared.
3. RDR is cleared to all zeros.
4. Internal Boolean code registers that hold the Boolean values defined by the
SET_BOOL graphic orders are cleared to all zeros.
If the RSR is loaded between the time an RGP error is detected and the time the soft-reset
is issued, the address stored in the RSR is lost. Additionally, if RDR information is needed,
the RDR must be read before an RGP soft-reset is executed. Due to the prefetching
characteristics of the RGP, and depending on the type of error, the address returned by the
RDR may be slightly beyond the source of the error.
When a graphic order is interrupted due to a band fault, all parameters necessary to resume
the data transfer at the point where the band fault occurred are written back into the display
list. In addition, the graphic order’s band number is incremented (or decremented for 180
°
pages) and written back into the display list to ensure that the graphic order is executed for
the next band. Since the hardware automatically updates graphic orders that generate band
faults, graphic orders that span multiple bands execute without any software intervention.
Once a graphic order has been updated after a band fault, the execution of the display list
continues with the next graphic order in the list.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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