[Amforth-devel] spi master mode?

[Erich W. <ew....@na...>]

Hello,

I'm adding external periphery to SPI of an atmega32 controller.

a. bit-bang mode

when bitbanging clock and setting mosi / reading miso, everything works fine.
==> my wiring and the external chip are ok.

b. using the builtin subsystem.

I set mosi and clk to output, and the select pin (PORTC.2) as well.

HOWEVER, I found it impossible to set SPCR to the desired values:

 > hex
  ok
 > $53 SPCR c!
  ok
 > SPCR c@ .
43  ok

The bit $10, which is apparently not set, ist the MSTR bit. That fits
the symtoms I'm seeing: "spirw" (available in core/words/spirw.asm)
never returns, because SPIF in register SPSR is never set. No wonder,
if we are not in master mode to begin with. The bit-bang version
never looks at SPSR and SPCR.

I found in the datasheet that the behaviour depends on whether /SS is
input and externally driven low or not while setting SPCR. However,
switching /SS to output does not change the situation.

This is the same in amforth 3.4 (where I found my old test), 3.8 or trunk.

Ideas?

Cheers,
Erich