Analog Devices ADSP-SC58 Series Hardware Reference Manual page 867

Data Transfer Modes
Figure 18-13: EPPI Delayed Frame Sync Generation
Ignoring Premature External Frame Syncs for Data Consistency
Once a frame has started with a VSYNC followed by an HSYNC (or both coming together), a line is tracked. When
the count expires, the state machine waits at the end of line for an HSYNC to come. With the arrival of the
HSYNC, the state machine starts tracking the next line, and so on.
The number of lines tracked is counted separately. Once the end of a frame is reached, the state machine waits there
for the next VSYNC/HSYNC combination. The next frame starts once they are sampled. Unfortunately, every in-
coming FS (VSYNC or HSYNC) resets the respective counters and the tracking starts all over (even if the FS signals
are premature). The result is incomplete data (or frames) to enter into memory through the PxP interface.
To correct this problem, the EPPI waits for a frame or line completion before considering any incoming FS as valid.
• Single FS mode and line tracking in dual FS mode – When a line is in progress, when HSYNC is detected
prematurely, it is ignored. A line track underflow event is generated.
• Dual FS mode – If a VSYNC is received when a frame is in progress, it is ignored. A frame track underflow
error (EPPI_STAT.FTERRUNDR) is generated.
Ignoring the FS ensures that once a frame starts, the amount of data that goes into the memory/PxP interface corre-
sponds exactly to the programmed data size in a frame.
Even if the premature FS is a valid FS, the state machine loses at most one frame and it recovers in the
NOTE:
subsequent FS. The FS to number of data going into the memory relationship is always maintained as
programmed.
When data underflow errors occur at the DMA interface, the EPPI does the following.
• If a premature line sync is detected, an LT underflow error is generated (EPPI_STAT.LTERRUNDR =1). All
further line track errors are ignored until the EPPI detects the next valid line sync.
• If a premature frame sync is detected, an FT underflow error is generated (EPPI_STAT.FTERRUNDR =1).
All further frame track and line track errors are ignored until the EPPI detects the next valid frame sync.
EPPI Event Control
The following sections describe how EPPI manages events.
18–28
PPI_CLK
PPI_EN
PPI_FS1
PPI_FS1D PPI_FS1W
PPI_FS1P
ADSP-SC58x/ADSP-2158x SHARC+ Processor Hardware Reference
PPI_FS1W
PPI_FS1P