Programming Tips
TVP4020
Programmers Reference Manual
140
this address range, and works towards the upper. For further information
see section §3.2.
7.1.3
Using PCI Disconnect under Programmed I/O
The PCI bus protocol incorporates a feature known as PCI Disconnect,
which is supported by P
ERMEDIA
. Once P
ERMEDIA
is in this mode, if the
host processor attempts to write to the full FIFO then instead of the write
being lost, the P
ERMEDIA
chip will assert PCI Disconnect. This in turn will
cause the host processor to keep retrying the write cycle until it
succeeds.
This feature allows faster download of data to P
ERMEDIA
since the host
need not poll the InFIFOSpace register. But it should be used with care
since whenever the PCI Disconnect is asserted, the bus is effectively
hogged by the host processor until such time as the P
ERMEDIA
frees up
an entry in its FIFO.
7.1.4
Using bus mastership (DMA)
It is expected that most P
ERMEDIA
boards will support PCI bus
mastership. This allows the on-board DMA of P
ERMEDIA
to be used to
copy data from host memory into the P
ERMEDIA
FIFO.
The use of PCI bus mastership has a number of benefits:
• PCI bus bandwidth utilization is generally much improved.
• PCI bus bandwidth is further improved because the driver software no longer needs to
poll the FIFO flags to find how many entries are empty, before loading it.
• Overall system performance may benefit through increased parallelism between
P
ERMEDIA
and the host, as the host can often perform useful work preparing the
next DMA buffer once it has initiated a DMA transfer.
See section §3.2.4 for more details on using DMA.
7.1.5
Improving performance with DMA
The use of DMA interrupts can significantly improve performance as
these allow useful work to be done in time which would be otherwise be
used by polling.
Having multiple DMA buffers is usually advantageous. The size and
number of buffers is dependent on OS dependent issues such as
context switch time.
7.1.6
Improving Texture Mapping performance
The use of interrupts can significantly improve the performance of
texture mapping operations. It achieves this by downloading textures 'on
demand'. That is during a texture mapping operation, if the required
texture map does not exist in local memory, an interrupt is generated so
Summary of Contents for TVP4020 PERMEDIA 2
Page 1: ...Texas Instruments TVP4020 PERMEDIA 2 Programmer s Reference Manual Issue 4 ...
Page 284: ...TVP4020 Programmers Reference Manual A Gouraud Shaded Triangle 275 ...
Page 292: ...TVP4020 Programmers Reference Manual Register Tables 283 ...
Page 314: ...TVP4020 Programmers Reference Manual Index 305 ...
Page 315: ...Index TVP4020 Programmers Reference Manual 306 Index ...
Page 323: ...Index TVP4020 Programmers Reference Manual 314 ...