[psas-avionics] lpc2378 SPI channel selection..

David H. Madden dhm at mersenne.com
Sat Aug 14 21:25:56 PDT 2010


On 08/14/2010 08:56 PM, Daniel Ferguson wrote:

> You'll notice that,
> SPI pin, MOSI(P0.18), is seemingly unexposed to the outside world.
> So from my fresh-faced perspective, SPI is unusable on this board as-is.

If I'm reading the lines right, P0.18 goes over to BUT2.  So it's not as 
easy as it could be, but you could probably tap it with a piece of 
wire-wrap wire.

> In case I truly cannot use SPI(sans SSP), I need a backup plan...
> SSP0 goes to the LCD. And, it's not exposed via headers as-is. so SSP0 is
> out.
>
> That leaves me with SSP1
> So, SSP1 will do, but it doesn't let me use the interrupts that the SPI/SSP0
> give me.

I found the LPC23xx manual...looks like there's a SPI port and two SSP 
ports, which can operate in SPI mode.  So...how are they pinned out? ...
Looks like SSP1 is pinned out to P0.[789], on EXT-2.  SSP0 shares pins 
with SPI.  SSP0 can also get pinned out to P1.23...which goes over to 
the LCD.  I haven't chased it all out, but I wouldn't be surprised if 
you can hook up SSP0 to the LCD by selecting some pins, and connect it 
somewhere else by selecting other pins.

I haven't read thru the SSP chapter, but it's not entirely unusual for 
one of two otherwise-identical peripherals to have a little extra love 
in the interrupt or control-line department.

If you absolutely need interrupts to write your code, you might be 
screwed, but IME on the LPCs, you can abstract stuff away pretty well, 
and just fake the interrupts by busy-waiting or whatever.  You can get 
your code running, and when you get the real hardware built, you 
shouldn't have _that_ much extra work to do.

What are you putting on the SPI bus?
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