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Subject: Re: ANNOUNCE: Rockbox emulates M-Bus car CD changer (Alpine and OEM)
From: [IDC]Dragon (idc-dragon_at_gmx.de)
Date: 2004-02-13


> If I understood correctly, there is a PIO connected to the remote pin.

Yes.

> I dont know if it is possible in the archos, but it might be possible to
> trigger an interrupt at each transition.

No, unfortunately the pin is not interrupt-capable. And this is where the
nice general concept collapses, sorry.

Under some circumstances it is possible to abuse the UART RX feature to have
an interrupt, like I do. RX waitts for a start condition (falling edge),
then with the set baudrate captures the start bit which must be low, some data
bits and optional parity, then the stop bit which must be high again. Is any
of the "must" is violated, it generates a framing error.
For my Alpine protocol this is usable, I can set the baudrate in a way that
start and stop condition are always fulfilled, but not in general.

Dirk-Andreas did the IR like this:
a) set RX to highest baudrate, so that it generates RX or error interrupt if
anything moves
b) if above comes, enable a high-speed "polling" timer interrupt for a
while, to sample the remote pin

> When the high level protocol decides to transmit data, it just disable the
> interrupt for the input and then it can drive the remote pin.

> This technique of setting the interrupt handler for each transition is
> used
> in the universal infrared receiver design. I think that it is generic
> enough
> to provide a general purpose remote control api.

For IR, yes. But I'm not following as far as generalizing CD changer
protocols, serial keyboards, etc. into that as well. Each should have it's own
low-level driver.

> I've read about the sony s-link, which seems very similar to the M bus
> encoding (pulses to encode 0 and 1) it is also compatible with this
> generic technique.
>
> The sony S-link seems more interesting to me because sony pilot changer
> are
> cheap and widespread. The protocol is also well documented. It is even
> possible to display song names.

I like that, but happen to have an Alpine.

Jörg

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