[mythtv-users] Re: MyIRBlaster - Myth Issues Only??

[Dan Wilga]

I have also experienced problems using LIRC to send IR signals 
through the serial port. I believe the reason is LIRC's reliance on 
the (low priority) RTC interrupt for timing. LIRC toggles a single 
serial port control line up to 56,000 times per second, to directly 
turn an LED on/off. If another thread takes control away from LIRC 
for too long, a pulse gets stretched and the IR device becomes 
confused.

However, this problem shouldn't affect devices like MyBlaster, 
because its software uses standard serial I/O to send information to 
the device. A single IR code consists of just a few bytes of data 
sent using a slow (compared to LIRC) baud rate of 19,200 bps. The 
MyBlaster then translates these few bytes into the many IR pulses 
necessary to control the device.

I'm really surprised, and somewhat disappointed, to hear that even 
MyBlasters have trouble. I was actually considering buying a 
MyBlaster or constructing something similar on my own using a 
microcontroller.

Maybe I'll set up a test to just send serial bytes in a predictable 
order and see if they get garbled or missed over time while Myth is 
displaying video.

My setup incudes a 3.0 GHz P4 running on an ASUS motherboard that use 
the ATI chipset. So none of that matches the original poster.

I am also using a PVR-250 and a PVR-350. There's no secondary video 
card; I'm using the onboard ATI video.
-- 
Dan Wilga                                         dwilga at mtholyoke.edu
Web Administrator                             http://www.mtholyoke.edu
Mount Holyoke College                                Tel: 413-538-3027
South Hadley, MA  01075            "Who left the cake out in the rain?"