readme.encoderwatchdog

神龙卡开发原代码

Reason for an encoder watchdog
------------------------------
On one hand, the SM2288 encoder will not crash easily, but high
bitrate and perturbed video input will make it more sensible to
crashing.

On the other hand, it's not acceptable that a user recording a 2h
movie gets it half for a few seconds signal quality defect.

As a consequence, private/encoderprivate.c contains some code to
restart the encoder automatically when it is in a state where it
should output data but does not.

This is an emergency measure only and the system stream at the
junction between bogus termination and emergency restart _will not be_
compliant with standards. We hope the decoding software will be
error-resilient enough to skip the defect.

In the worst case about five seconds of video will be lost.

What are the conditions to trigger the watchdog?
------------------------------------------------
The watchdog is run in the following cases:

1- immediately, if one of the following TX_FIFO message occurs:
                case 0x01e0: // ?
		case 0xaff4: // discarded gop
		case 0xeeb0: // VOBU error
		case 0xeeb4: // VOBU error
		case 0xeef3: // end frame flag lacking
because they have proved to stall encoder immediately anyways.

2- every ENCODER_WATCHDOG_UPDATE_PERIOD_US microseconds (currently,
5000000 microseconds), the byte count is compared to the previous test
byte count. If both numbers are equal, the encoder is considered as
stalled (crashed). 

What does the watchdog?
-----------------------
The watchdog runs encoderprivate_softreset(), meaning the current
encoding parameters are kept as close as possible to the parameters
that were used before crashing (they are not reset to params.h). This
means an error-resilient decoder will go on demuxing the same system
type, decoding same audio type, etc.

The watchdog is entirely handled in kernel mode. From the user
application point of view, the bitstream will be invalid at some
point, and the happening REALMAGICHWL_HAPPENING_ENCODER_CRASH may be
tested regularly to get ready for some woes. The user can choose to
never test REALMAGICHWL_HAPPENING_ENCODER_CRASH and trust the recovery
abilities of its playback software.

Details of implementation (see code in private/encoderprivate.c)
----------------------------------------------------------------
The test 2- is, of course, disabled when the encoder is in STOP mode
or PAUSE mode. `pE->eW.encoderRunning' is used to distinguish between
these cases.

Since it's not possible to run START before having uploaded a correct
parameter list (RUA_ENCODER_RESET() or ENCODER_PARAMSAPPLY property),
the situation when 0xfeed is received and pE->eW.encoderRunning==1 is
the valid test to enter // actual encoder watchdog part II

To disable the watchdog, replace:

// actual encoder watchdog part I
	if (triggerSoftReset) {

by

// actual encoder watchdog part I
	if (0) {