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MT9T111_DG - Rev. B 9/10 EN
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MT9T111: Developer Guide
JPEG Encoder
Preliminary
Transfer Modes
Two JPEG transfer modes are supported for different output streams:
• Continuous mode
• Spoof mode
The output buffer module takes inputs from different sources—the color pipe bypass
stream, the JPEG bypass stream, and the JPEG compressed stream. Each data stream
source may have its own transfer mode, which is shown in Table 17.
Bypass Mode
In this scenario, the hardware ignores the option of changing the clock speed depending
on data rates. The clock remains at the frequency of PCLK1. However, the software can
slow down PCLK1 by programming the output buffer PCLK1 configuration register. It is
the responsibility of the user to guarantee that the buffer does not overflow or underflow.
CCIR markers can be optionally inserted. However, because the markers SOF and EOF
are carried on data before FV is asserted, and after FV is asserted; SOL and EOL markers
are carried on data before LV is asserted and after LV is de-asserted, CCIR markers can
NOT be guaranteed to be transferred on the MIPI/CCP interface. This feature only
applies to the parallel output port.
Continuous Mode
The JPEG output clock can be configured to be either continuous or gated off while LV is
de-asserted. The JPEG output clock can also be optionally gated off between frames to
save power.
The JPEG data stream implements two markers, SOI (0xFFD8) and EOI (0xFFD9), which
can be optionally inserted before and after valid JPEG data, respectively. SOI and EOI
can be inserted either inside or outside the FV assertion period, but always inside the LV
assertion period.
The adaptive clock switching feature is also supported. The PCLK changes according to
the output buffer FIFO fullness status.
When the thumbnail asserts a request and the FIFO is less than 5/8 full, the output
buffer serves the thumbnail immediately until the end of the thumbnail line. Then the
output buffer switches back to JPEG data if there is any. When the thumbnail asserts a
request and the FIFO is more than 5/8 full, JPEG data has higher priority. The output
buffer does not service the thumbnail request until the FIFO drops below 5/8 full.
JPEG status information can be appended at the end of JPEG/Thumbnail stream.
Table 17:
Transfer Modes and Sources
Source/Mode
Bypass Mode
R0x3C52[1:0] = “10”
Continuous Mode
R0x3C52[1:0] = “00”
Spoof Mode
R0x3C52[1:0] = “01”
Color pipe bypass stream
R0x3C50[1:0] = “10”
X
JPEG bypass stream
R0x3C50[1:0] = “01”
X
JPEG compress stream
R0x3C50[1:0] = “00”
X
X