is CIA port A bit 1 (filter) readable?

jotd · 20 June 2019, 00:06

in some game I saw:

Code:

    TST.B    some_flag     
    BEQ.S    LAB_0598   
    BSET    #1,CIAA_PRA   
    BRA.S    LAB_0599   
LAB_0598:
    BCLR    #1,CIAA_PRA   
LAB_0599:

but is it possible to just toggle it ?:

Code:

  BCHG    #1,CIAA_PRA

I suppose that all (except 6 & 7 maybe) bits are readable as BSET/BCLR already read the whole byte to just change 1 bit. Is that bit readable too?

Thomas Richter · 20 June 2019, 01:20

Quote:

Originally Posted by jotd

Is that bit readable too?

Yes. CIA port bits are both read and write at the same address, unlike the custom chips where the direction is implicit in the address.

Photon · 07 July 2019, 22:44

I have assumed no, since I've seen code that saves and restore hardware registers but not the state of this bit. Interesting.

Probably some structure in audio.device or elsewhere can be used to get the last state set by some library call, though?

Thomas Richter · 08 July 2019, 08:05

Unfortunately, operating system support for this bit is zero. There is nothing, nowhere.

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20 June 2019, 00:06	#1
jotd This cat is no more Join Date: Dec 2004 Location: FRANCE Age: 52 Posts: 8,163	is CIA port A bit 1 (filter) readable? in some game I saw: Code: TST.B some_flag BEQ.S LAB_0598 BSET #1,CIAA_PRA BRA.S LAB_0599 LAB_0598: BCLR #1,CIAA_PRA LAB_0599: but is it possible to just toggle it ?: Code: BCHG #1,CIAA_PRA I suppose that all (except 6 & 7 maybe) bits are readable as BSET/BCLR already read the whole byte to just change 1 bit. Is that bit readable too?

07 July 2019, 22:44	#3
Photon Moderator Join Date: Nov 2004 Location: Eksjö / Sweden Posts: 5,602	I have assumed no, since I've seen code that saves and restore hardware registers but not the state of this bit. Interesting. Probably some structure in audio.device or elsewhere can be used to get the last state set by some library call, though?

08 July 2019, 08:05	#4
Thomas Richter Registered User Join Date: Jan 2019 Location: Germany Posts: 3,215	Unfortunately, operating system support for this bit is zero. There is nothing, nowhere.

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