PNX1300/01/02/11 Data Book
Philips Semiconductors
7-16
PRELIMINARY SPECIFICATION
7.16.1
VO Status Register (VO_STATUS)
The VO_STATUS register is a read-only register that
shows the current status of the EVO. Its fields are shown
in
Figure 7-29
and
Table 7-6
.
VO_STATUS[4] is now hard-wired to
‘
1
’
. This allows soft-
ware to determine if the unit is an EVO unit (containing
extra MMIO registers) or a TM-1000 VO unit, as follows.
In the TM-1000, this bit is a copy of the HBE flag
(VO_STATUS[5]). In the EVO unit, it is hard-wired to
‘
1
’
.
Software can use this bit to determine the type of (E)VO
unit
by
clearing
the
VO_STATUS[4]. If the bit remains
‘
1
’
, the unit is an EVO.
HBE
bit
then
reading
Table 7-6. VO_STATUS
—
status register fields
Field
Description
CUR_Y
Current Y.
Image line index of the current line in the current field being output by the EVO. CUR_Y reflects the current state of
the Image Line Counter. CUR_X and CUR_Y form a single 24-bit output data byte counter (CUR_X is the counter
LSBs) when the EVO is in data-streaming or message-passing mode. This counter reflects the status of the SIZE
counter for the currently active buffer. The two LSBs of this counter are not valid for reading during transfers; only
the upper 22 bits (the word count) are valid.
Current X.
Image pixel index of the most-recently-output pixel. CUR_X reflects the current state of the Image Pixel Counter.
Buffers 1 and 2 Empty.
These bits are valid in video-refresh, data-streaming and message-passing modes.
In video-refresh modes, only Buffer 1 is used. BFR1_EMPTY indicates that the last byte of a field has been
transferred. It is actually raised at the completion of the transmission of the Overlap area of the field, as shown in
Figure 7-31
. At this point, software should assign a new field of imagery to {Y,U,V}_BASE_ADR and perform a
BFR1_ACK. If BFR1_EMPTY is not cleared by BFR1_ACK before the active video area of the next field starts to
be emitted, the EVO sets the URUN bit.
In data-streaming mode, BFR1_EMPTY and BFR2_EMPTY indicate that the last byte in their corresponding
buffer has been transferred. When BFR1_EMPTY or BFR2_EMPTY is set, transfer stops from the corresponding
buffer.
In message passing mode, BFR1_EMPTY signals completion of message transmission.
These bits cause an interrupt if their interrupt-enable bits are set. One interrupt per buffer is signaled.
Highway Bandwidth Error.
HBE is set when the highway fails to respond in time to a highway read request and data was not ready in time to be
set on EVO data lines. HBE can be set in both image- and data-transfer modes. HBE indicates insufficient band-
width was requested from the highway arbiter.
EVO unit indicator.
This bit allows software to determine if the unit is an EVO (containing extra MMIO registers) or a TM-1000 VO unit.
In the TM-1000, this bit is a copy of the HBE flag. In the EVO unit, it is hard-wired to
‘
1
’
. Software can easily deter-
mine the type of video output unit by clearing the HBE bit then reading this bit.
Y threshold.
In video-refresh modes, YTR indicates that the Image Line Counter value is equal to the Y_THRESHOLD value in
VO_YTHR. The Y_THRESHOLD value can be set to provide an interrupt on any line in the valid image area.
Underrun.
In video-refresh and data-streaming mode, this bit indicates that the CPU did not perform an acknowledge to indi-
cate updated address pointers for the next field or buffer in time for continuous image or data transfer URUN causes
an interrupt if the corresponding interrupt-enable condition is set.
In video-refresh modes, URUN indicates that the SAV code marking beginning of active video has been gener-
ated without BFR1_ACK being set by the CPU. (Setting BFR1_ACK to
‘
1
’
clears BFR1_EMPTY). In this case,
video refresh continues with previous address pointers.
In data-streaming mode, URUN indicates the last byte in the active buffer was transferred, and no BFR1_ACK or
BFR2_ACK occurred to enable the next buffer. In this case, transfer continues with previous address pointers.
Field 2 or Buffer 2 active.
In data-streaming mode, FIELD2 = 0 when Buffer 1 is active; FIELD2 = 1 when Buffer 2 is active.
In video-refresh modes, FIELD2 indicates that the EVO is actively sending out a video image for Field 2, as
defined by
Figure 7-31
.
Vertical blanking.
Indicates that the EVO is in a vertical-blanking interval. VBLANK is asserted only in video-refresh modes.
CUR_X
BFR1_EMPTY
BFR2_EMPTY
HBE
1
YTR
URUN
FIELD2
VBLANK