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Camera ISP Basic Programming Model
6.5.8.4
Camera ISP Resizer Register Accessibility During Frame Processing
There are two types of register access in the resizer.
•
Shadow registers: These registers/fields can be read and written (if the field is writable) at any time.
However, the written values take effect only at the start of a frame. Reads return the most recent write,
even though the settings are not used until the next start of frame.
The shadowed registers are:
–
–
–
–
–
•
Busy-lock registers
–
All registers EXCEPT the shadowed registers belong to this category.
–
Busy-lock registers cannot be written when the module is busy. Writes are allowed, but no change
occurs in the registers (blocked writes from hardware perspective; allowed write from software
perspective).
–
After the
[1] BUSY bit is reset to 0, the busy-lock registers can be written.
The ideal procedure for changing the resizer registers is:
IF (
[1] BUSY == 0) OR IF
(EOF interrupt occurs)
DISABLE RESIZER
CHANGE REGISTERS
ENABLE RESIZER
6.5.8.5
Camera ISP Resizer Inter-Frame Operations
Between frames, it may be necessary to modify the memory pointers before processing the next frame.
Because the
[0] ENABLE bit and memory pointer registers are shadowed, these modifications
can occur any time before the end of the frame, and the data is get latched in for the next frame. The
MPU subsystem can perform these changes on receiving an interrupt.
NOTE:
The firmware must compute and upload the filter coefficients. If polyphase resampling is
used, a different set is required when changing between 4-tap and 7-tap modes, and with
different downsampling factors; all upsampling factors can share the same set of coefficients.
Do not change any busy-lock registers while the resizer is operating. Specifically, when
back-to-back resizes require changes in any busy-lock registers (such as the coefficients,
resizing ratios, input and output sizes), users must wait for the first resize to complete. The
following section describes some scenarios where this is required.
6.5.8.5.1 Camera ISP Resizer Multiple Passes for Large Resizing Operations
The resizer supports multiple passes of processing for large resizing operations. "Large" has the following
meanings:
•
Wider output than 4096 pixels: This works only in memory input mode. Input can be partitioned into
multiple resizer blocks, and each block is separately resized and stitched together. Having input/output
memory line offsets, input starting pixel and starting phase are essential to make this work. The basic
idea is to begin subsequent slices at exactly where previous images leave off. The starting phase and
pixel registers can be programmed to this exact location.
•
Larger than 4x upsampling: Resizing can be applied in multiple passes. For example, 10x upsampling
can be realized by first a 4x upsampling, then a 2.5x upsampling. The first pass can be performed
on-the-fly with the preview engine. The second pass can be performed only with input from memory,
and for 10x digital zoom; there is time outside the active picture region to perform the second pass.
1287
SWPU177N – December 2009 – Revised November 2010
Camera Image Signal Processor
Copyright © 2009–2010, Texas Instruments Incorporated
