1.1 --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
     1.2 +++ b/README	Fri Feb 23 13:29:37 2018 +0200
     1.3 @@ -0,0 +1,27 @@
     1.4 +Amiga floppy boot test
     1.5 +----------------------
     1.6 +Bootblock code in src/boot/boot.s uses the Amiga exec in ROM to load the
     1.7 +flat binary image from from the first N sectors to address 0x10000, and jumps
     1.8 +there. The size of the binary is patched immediately before the first
     1.9 +instruction of the boot code by tools/mk_adf.py.
    1.10 +
    1.11 +Linkscript puts code from the .startup segment (src/startup.s) at the load
    1.12 +address, and it starts by setting the trap0 exception vector to point to the
    1.13 +next instruction and executes a trap 0, to enter supervisor mode and take
    1.14 +complete control of the system. Then it clears .bss, sets the stack and calls
    1.15 +the C main function.
    1.16 +
    1.17 +A few words about the graphics hack
    1.18 +-----------------------------------
    1.19 +The IFS fractal is calculated in 16.16 fixed point, using a mersenne twister
    1.20 +random number generator (src/rng.c) for picking an IFS transformation to do each
    1.21 +time. Two bitplanes are enabled both pointing to the same IFS pixel buffer, with
    1.22 +a few scanlines offset and a different per-pixel scroll (data fetch delay) in
    1.23 +BPLCON1. The palette is set up in a way to give priority to bitplane 0, i.e. use
    1.24 +green for pixels with bit 0 set, and use a shadow color for pixels which have
    1.25 +only bit 1 set. This gives the illusion of a shadow layer.
    1.26 +
    1.27 +Serial debug output
    1.28 +-------------------
    1.29 +Serial comm needs RTS/CTS (hardware) flow control.
    1.30 +  stty 38400 crtscts cs8 -parenb -ixon -ixoff raw -iutf8 -F /dev/ttyUSB0