Accessory port

[geekmaster]

Originally Posted by mmatej

Thanks. Do yo know how to control LEDs using any similiar method?

There is an LED diagnostic in u-boot bist (using the serial port) that can flash out Morse code "okay" or "fail" on the LEDs. You could look in the u-boot source code for that.

Direct control of hardware needs to be in kernel mode, so would either need a custom loadable kernel module, or a custom kernel loaded with kexec (unless you can find an ioctl() call to do what you want).

I would like to output PWM sound on the LEDs (stereo using the yellow and green LEDs). You could recover the audio with color filters and a pair of photosensors feeding an audio amplifier (powered computer speakers?).

Of course, we can also use a USB OTG sound adapter, with appropriate hardware. I ordered some $1.35USD devices from an ebay store to use on a K4 (when I get some time). You can buy USB host mode cables for less thatn $1USD, or you can just cut a microUSB plug from a cord and solder it into the USB sound adapter.

Or you could use "WiFi Sound" (pipe raw sound to a host PC over WiFi).

[mmatej]

Originally Posted by geekmaster

There is an LED diagnostic in u-boot bist (using the serial port) that can flash out Morse code "okay" or "fail" on the LEDs. You could look in the u-boot source code for that.

Direct control of hardware needs to be in kernel mode, so would either need a custom loadable kernel module, or a custom kernel loaded with kexec (unless you can find an ioctl() call to do what you want).

I would like to output PWM sound on the LEDs (stereo using the yellow and green LEDs). You could recover the audio with color filters and a pair of photosensors feeding an audio amplifier (powered computer speakers?).

Of course, we can also use a USB OTG sound adapter, with appropriate hardware. I ordered some $1.35USD devices from an ebay store to use on a K4 (when I get some time). You can buy USB host mode cables for less thatn $1USD, or you can just cut a microUSB plug from a cord and solder it into the USB sound adapter.

Or you could use "WiFi Sound" (pipe raw sound to a host PC over WiFi).

There is also LED diagnostic in system diags, which can blink the LEDs, so it must be possible to control them within userspace. Stupid that they haven't released diags prog source. Do you think if we asked them, they would provide it?
That idea with PWM on LEDs isn't bad, but LEDs have also some time to turn off completely (but I don't know very much about transfer via light system).
Have somebody tested that host mode? I don't know how to switch it so.

[geekmaster]

Originally Posted by mmatej

There is also LED diagnostic in system diags, which can blink the LEDs, so it must be possible to control them within userspace. Stupid that they haven't released diags prog source. Do you think if we asked them, they would provide it?
That idea with PWM on LEDs isn't bad, but LEDs have also some time to turn off completely (but I don't know very much about transfer via light system).
Have somebody tested that host mode? I don't know how to switch it so.

Diags is not GPL, so probably not...

Incandescent bulbs take awhile to turn off because the filament needs to cool. Fluorescent bulbs take awhile to turn off because the phosphor had a decay rate. Some white LEDs contain a phosphor that is activated by an internal blue LED, so those white LEDs are actually a type of fluorescent light.

Ordinary LEDs turn on and off fast enough to send Radio Frequencies over them, so they would certainly be good enough for audio use.

[mmatej]

Originally Posted by geekmaster

Diags is not GPL, so probably not...

Incandescent bulbs take awhile to turn off because the filament needs to cool. Fluorescent bulbs take awhile to turn off because the phosphor had a decay rate. Some white LEDs contain a phosphor that is activated by an internal blue LED, so those white LEDs are actually a type of fluorescent light.

Ordinary LEDs turn on and off fast enough to send Radio Frequencies over them, so they would certainly be good enough for audio use.

Really? I've been always imagining that they are like small lamps.. (after all, they have small filament wire which actually emits the light, or not??)

[geekmaster]

Originally Posted by mmatej

Really? I've been always imagining that they are like small lamps.. (after all, they have small filament wire which actually emits the light, or not??)

Imagination guides your research, but does not replace it.

[mmatej]

Originally Posted by geekmaster

Imagination guides your research, but does not replace it.

Yeah, next time I will verify my thoughts if I am not sure!