Atari STE SIMM mixer by David Hoggan

Lets STE configure 2.5 Megs properly

@atari

Published in 

atari

 · 17 Mar 2021

  
* STE SIMM mixer by David Hoggan 
* Lets STE configure 2.5 Megs properly 
* MUST BE FIRST IN AUTO FOLDER! 

* This program asssumes 2Mb in bank 0 and 0.5Mb in bank 1. 
* It has been found that the other way around doesn't work 
* - the MMU configures to a 1Mb machine. 

* Install your SIMMs as follows: 
* 
* (back of STE) 
* 
* |--  1meg SIMM  --| 
* |-- .5meg SIMM  --| 
* |--  1meg SIMM  --| 
* |-- .5meg SIMM  --| 
* 
* (front of STE) 

    clr.l   -(sp) 
    move.w  #32,-(sp)       Switch to super mode 
    trap    #1 
    addq.l  #6,sp 

    cmp.l   #$280000,$42E   RAM <= 2.5 megs? 
    ble     already         If so, nothing to do 
    cmp.b   #9,$424         Is it installed properly? 
    bne     already         If so, nothing to do 

    move.l  #$280000,$42E   Set phystop 
    move.l  $4F2,a0         Find reset address 
    jmp     (a0)            Reset system 

already: move.l d0,-(sp)        Returned stack 
    move.w  #32,-(sp)       Switch back to user mode 
    trap    #1 
    addq.l  #6,sp 
    clr.w   -(sp)           Back to TOS 
    trap    #1