
TM1100 Preliminary Data Book
Philips Semiconductors
6-12
PRELIMINARY INFORMATION
File: vin.fm5, modified 7/24/99
6.7
HIGHWAY LATENCY AND HBE
biter terminology used here. Video In uses internal buff-
ering before writing data to SDRAM. There are two inter-
nal buffers, each 64 entries of 32 bits.
In fullres mode, each internal buffer is used for 128 Y
samples, 64 U samples and 64 V samples. Once the first
internal buffer is filled, 4 highway transactions need to
occur before the second buffer fills completely. Hence,
the requirement for not loosing samples is:
4 requests have to be served within 256 Video In
clock cycles.
For the typical CCIR601 resolution NTSC or PAL 27 MHz
Video In clock rate, the latency requirement is 4 requests
in 25600/27 = 9481 ns, which can be used as one re-
quest every 2370 or with a TM1100 SDRAM clock speed
of 100 MHz, every 237 SDRAM clock cycles. The one re-
quest latency is used to define the priority raising value
In halfres mode, the Y, U and V decimation by 2 takes
place before writing to the internal buffers. Hence, the re-
quirement for not loosing samples is:
4 requests have to be served within 512 Video In
clock cycles.
For halfres subsampling NTSC or PAL 27 MHz Video In
clock rate and TM1100 SDRAM clock speed of 100 MHz,
latency is 4 requests in 51200/27 = 18962 ns (1896 high-
way clock cycles) or one request every 4740 ns (474
SDRAM clock cycles).
For raw8 capture and message passing mode, each in-
ternal buffer stores 64 samples at the incoming Video In
clock rate. The latency requirement is:
1 request has to be served every 64 Video In clock
cycles.
For the raw10 capture modes, each internal buffer stores
32 samples. Hence, the requirement for not loosing sam-
ples is:
1 request has to be served every 32 Video In clock
cycles.
For a 38 MHz data rate on the incoming 10-bit samples
and a TM1100 SDRAM clock speed of 100 MHz, latency
for the highway should hence be set to guarantee less
than 3200/38 = 842 ns (84 SDRAM clock cycles) per
clock cycles which cannot be met if any of the other pe-
ripherals is enabled.
Table 6-4 summarizes the maximum allowed highway
latency, in SDRAM clock cycles) to guarantee that no
ACTIVE = BUF2
BUF1FULL
ACTIVE = BUF1
ACTIVE = BUF2
ACTIVE = BUF1
BUF2FULL
BUF1FULL
BUF2FULL
raise OVERRUN*
* OVERRUN and OVERFLOW are sticky flags. They get set,
but they do
not affect operation. They can only be cleared by
software, by writing a ‘1’ to ACK_OVR or ACK_OVF.
ACK1 & ~ACK2
ACK1 & ACK2
~AC
K1 &
AC
K2
EO
M
EOM
ACK1
EOM
ACK2
RESET
No EOM
raise OVERFLOW*
(
No EOM
raise OVERFLOW*
(
Figure 6-18. Video In message passing mode major states.