[lm-sensors] Black box flight recorder for Linux
khc at pm.waw.pl
Thu Jun 8 01:52:42 CEST 2006
Andy Green <andy at warmcat.com> writes:
> A whole other way forward is to consider to replace the EEPROM from
> the original proposal (which does provide its own advantages such as
> simplicity, I accept) with something else that ends up on another
> PC. In this concept some logic presents a fake I2C peripheral to the
> DDC interface at an I2C address of our choosing. This logic acts as a
> bidirectional "UART" type of thing, allowing transfer of data in both
> directions between the Linux box being debugged and another PC.
Right. I think one could use something like ATMEL 89F2051 (20-pin 8051
non-SMD clones with flash and hardware UART) or something similar.
Client I2C is difficult in Linux (using general purpose I/O port) but
with a dedicated CPU it's not a problem (not sure about 400 kHz access).
Well, that's a bit more complicated. I'm not going to try that on
an experimental PCB :-)
> However this would be much simpler, not even needing RAM. It can hook
> to the second PC by the same I2C method, parallel printer port, RS232
> or USB depending on the level of complexity of the design.
> I guess the link will feel quite like a 9600 or 19200 baud serial port
> in terms of throughput.
Depends on I2C. With something like 400 kHz it should be faster,
probably like 115200.
> Maybe this effort is considered too esoteric, but it seems to me to be
> a reason to keep the DDC access drivers standalone, the
> hardware-specific framebuffer drivers can call through to them and we
> can use them in a clean way. I realize this is a bit of a late
> objection and that there was not previously much point to keeping them
> as separate things in the world.
Actually we have:
- the Xserver "hardware access" issue
- now the I2C bus driver
- frame buffer
To avoid conflicts we really need them managed by a single driver.
Probably the GGI (KGI?) should be revisited?
Long-term project, unfortunatelly, but I think we'll have to do that
The I2C, graphics subsystem and DRI/DRM could be sub-modules, with
the master module only keeping track of hardware access, mode
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