Re: [Freemint-discuss] Disassembly of TOS 1.00 with Ghidra

[Thorsten O. <ad...@th...>]

Other funny thing i just realized: the original version of the alcyon 
assembler was not able to assemble short absolute addressing modes, which 
saves 2 bytes when acessing system variables or I/O addresses. In TOS 2.x and 
above they used mas instead, but in older versions this was worked around by 
setting a5 to 0 and use that as a base register. However in TOS 1.00, they 
missed a lot of places where this mode could be used, sometimes even inside 
one instruction:

vsetscreen:
[00fc0982] 4aaf 0004                 tst.l      4(a7)
[00fc0986] 6b06                      bmi.s      $00FC098E
[00fc0988] 2b6f 0004 044e            move.l     4(a7),1102(a5)
[00fc098e] 4aaf 0008                 tst.l      8(a7)
[00fc0992] 6b10                      bmi.s      $00FC09A4
[00fc0994] 13ef 0009 ffff 8201       move.b     9(a7),$FFFF8201
[00fc099c] 13ef 000a ffff 8203       move.b     10(a7),$FFFF8203
[00fc09a4] 4a6f 000c                 tst.w      12(a7)
[00fc09a8] 6b24                      bmi.s      $00FC09CE
[00fc09aa] 1b6f 000d 044c            move.b     13(a7),1100(a5)
[00fc09b0] 6100 fd74                 bsr        $00FC0726
[00fc09b4] 13ed 044c ffff 8260       move.b     1100(a5),$FFFF8260   <---
[00fc09bc] 426d 0452                 clr.w      1106(a5)
[00fc09c0] 4eb9 00fc a7e2            jsr        esc_init
[00fc09c6] 33fc 0001 0000 0452       move.w     #$0001,$00000452
[00fc09ce] 4e75                      rts