1 Amiga floppy boot test

2 ----------------------

3 Bootblock code in src/boot/boot.s uses the Amiga exec in ROM to load the

4 flat binary image from from the first N sectors to address 0x10000, and jumps

5 there. The size of the binary is patched immediately before the first

6 instruction of the boot code by tools/mk_adf.py.

7

8 Linkscript puts code from the .startup segment (src/startup.s) at the load

9 address, and it starts by setting the trap0 exception vector to point to the

10 next instruction and executes a trap 0, to enter supervisor mode and take

11 complete control of the system. Then it clears .bss, sets the stack and calls

12 the C main function.

13

14 A few words about the graphics hack

15 -----------------------------------

16 The IFS fractal is calculated in 16.16 fixed point, using a mersenne twister

17 random number generator (src/rng.c) for picking an IFS transformation to do each

18 time. Two bitplanes are enabled both pointing to the same IFS pixel buffer, with

19 a few scanlines offset and a different per-pixel scroll (data fetch delay) in

20 BPLCON1. The palette is set up in a way to give priority to bitplane 0, i.e. use

21 green for pixels with bit 0 set, and use a shadow color for pixels which have

22 only bit 1 set. This gives the illusion of a shadow layer.

23

24 Serial debug output

25 -------------------

26 Serial comm needs RTS/CTS (hardware) flow control.

27 stty 38400 crtscts cs8 -parenb -ixon -ixoff raw -iutf8 -F /dev/ttyUSB0