Channel Change

Latency

Latency of the IRTek

  • The time involved with the IrTek receiving the serial command (at its port) and sending the IR code is about:
  • (12 data bytes * ( 8 data + 1 start + 2 stop bits)/ 115200 baud ~= 0.1 ms
  • This is not really a consideration to Channel Change measurements which are in the tens of milliseconds.

Other things that affect latency:

  • Software script output buffers flushing
  • USB Serial port communication
  • IP Network communications

Channel Change Tests

Channel Change Test 1

Ideally for an empirical measurement of Channel Change (CC), the settop could have software instrumentation to send a RS232 control line change directly to the UART hardware register at the start of the (CC) software process. That line would power a visible LED mounted to the side of a TV monitor. A TV camera recording of both the TV screen and the LED would be taken. Using a video editing tool, the exact number of frames between the start of the CC software (LED On) and the actual new channel video shown could be measured. This test would be independent and agnostic to IR signals and IR decoder software.

Channel Change Test 2

This test is the same as Test 1, but with no software instrumentation needed. The IR output drives an IR LED and visible LED mounted to the side of a TV monitor. A video editing tool can give you the exact number of frames between the start of the IR LED and the actual new channel video. This measurement would include the software IR decoding time.

Channel Change Test 3

Assumptions about when the IR decode software actually sends the CC event to the CC software must be made. For the SA classic and most other remotes, the assumed delay between the start of the IR signal and the start of the CC software process is about 100 ms.

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License