TVP4020
Programmers Reference Manual
Programming Model
21
PERMEDIAData
data;
// wait for DMA to complete
while (*DMACount != 0) {
poll or wait for interrupt
}
while (*InFIFOSpace < 2) {
;
// wait for free space in the FIFO
}
// enable sync output and send the Sync command
data.Word = 0;
data.FilterMode.Synchronization = 0x1;
FilterMode(data.Word);
Sync(0x0);
/* wait for the sync output data */
do {
while (*OutFIFOWords == 0)
;
// poll waiting for data in output FIFO
} while (*OutputFIFO != Sync_tag);
Initially, we wait for DMA to complete as normal. We then have to wait
for space to become free in the FIFO (since the DMA controller actually
loads the FIFO). We need space for 2 registers: one to enable
generation of an output sync value, and the Sync command itself. The
enable flag can be set at initialization time. The output value will be
generated only when a Sync command has actually been sent, and
P
ERMEDIA
has then completed all processing.
Rather than polling, it is possible to use a Sync interrupt as mentioned in
the previous section. As well as enabling the interrupt and setting the
filter mode, the data sent in the Sync command must have the most
significant bit set in order to generate the interrupt. The interrupt is
generated when the tag or data reaches the output end of the Host Out
FIFO. Use of the Sync interrupt has to be considered carefully as
P
ERMEDIA
will generally empty the FIFO more quickly than it takes to set-
up and handle the interrupt.
3.5
Host Memory Bypass
Normally, the host will access memory indirectly via commands sent to
the P
ERMEDIA
FIFO interface. However, P
ERMEDIA
does provide the whole
memory as part of its address space so that it can be memory mapped
by an application. Access to the memory via this route is independent of
the P
ERMEDIA
FIFO.
Содержание TVP4020 PERMEDIA 2
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