Motorola MPC860 PowerQUICC User Manual page 984

Part VI. Debug and Test
The sequencing error encoding indicates that the inputs from the external development tool
are not what the development port and/or the core was expecting. There are two possible
causes for this error:
¥ The processor was trying to read instructions and data was shifted into the
development port.
¥ The processor was trying to read data and an instruction was shifted into the
development port.
Nonetheless, the port terminates the read cycle with a bus error. In turn, this bus error causes
the core to signal that an interrupt exception occurred. Because a status of sequencing error
is of higher priority than an exception, the port reports the sequencing error Þrst and the
core interrupt on the next transmission. The development port ignores the command,
instruction, or data shifted in while the sequencing error or core interrupt is shifted out. The
next transmission, after all error status is reported to the port, should be a new instruction,
trap enable, or command.
The interrupt occurred encoding indicates that the core encountered an interrupt during the
execution of the previous instruction in debug mode. Interrupts may occur as the result of
instruction execution (such as unimplemented opcode or arithmetic error), because of a
memory access fault, or from an unmasked external interrupt. When an interrupt occurs the
development port ignores the command, instruction, or data shifted in while the interrupt
encoding was shifting out. The next transmission to the port should be a new instruction,
trap enable, or debug port command. Finally, the null encoding indicates that no data was
transferred from the core to the development port shift register.
37.3.2.5.3 Fast Download Procedure
The fast download procedure downloads a block of data from the debug tool into the system
memory by repeating the sequence of transactions shown in Figure 37-12 from the
development tool to the debug port for the number of data words to be downloaded.
INIT:
repeat:
until here
Figure 37-12. Download Procedure Code Example
In this example, RX = r31 and RY = r30. The sequence is repeated until the end download
procedure command is issued to the debug port. GPR31 temporarily stores the data value.
Before issuing the start download procedure command, the value of the Þrst memory block
37-34
Save RX, RY
RY <- Memory Block address- 4
¥¥¥
mfspr RX, DPDR
DATA word to be moved to memory
stwu RX, 0x4(RY)
¥¥¥
Restore RX,RY
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