B channel DMA enabled during line mode?

[mc6809e]

Old thread, but I found this in an old usenet post:

In article <2pjom5$d...@hpsystem1.informatik.tu-muenchen.de>, fisc...@Informatik.TU-Muenchen.DE (Juergen "Rally" Fischer) writes:
> I made the same experiences. No pattern reload in line mode. Reloading with cpu
This is NOT TRUE! I have done it! But it works too slow....sorry...
You may start the B channel (as usual, in CONx), but you are limited to where the
lines can go. The BLTBMOD must be 2, and you get the restrictions of this, as the
BLTBMOD is used as something else. You CAN actuallu draw lines with angels about
0,45,90,135,180,225,270,315,360 degrees. The B pos is incremented (a word) in
every pixel, and the pixel is shifted:

bdata: $8000 Set the start bit in one of the CONx regs (can't remember wich)
$4000
$2000
$efff
... This would read the pattern 1110 if startpos is 15, and 0001 if the startpos
is not 15. Drawing like this:

.
.
.
. Should do it... (some modulo changes on each line are needed)
(This needs interleaved planes!)

Too sad it's too slow...

The post seems to suggest that if BLTBMOD is 2, then a fetch happens for B channel into B data register (data is also shifted).