Talk:Controller reading code: Difference between revisions

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(→‎Removed last-frame compromise: follow-up, it was determined unsafe against DPCM in 2023)
 
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See: [[Talk:Standard_controller#Reorganization_needed_with_Controller_Reading]]
See: [[Talk:Standard_controller#Reorganization_needed_with_Controller_Reading]]
== Removed last-frame compromise ==
This code appeared in the [[Controller Reading#DPCM Safety using Repeated Reads|DPCM Safety using Repeated Reads]] section.
I have removed it, because I think it hurts comprehension for new readers who may not understand
what they are trading away to save a few cycles they may not need.
There's probably a place for this code somewhere, but I don't think it belongs in the middle of the article,
and certainly not in lieu of a simpler and more standard example.
I left a description of the technique, but not the code. - [[User:Rainwarrior|Rainwarrior]] ([[User talk:Rainwarrior|talk]]) 13:14, 16 April 2019 (MDT)
Code:
<pre>
last_frame_buttons1 = $00
last_frame_buttons2 = $01
first_read_buttons1 = $02
first_read_buttons2 = $03
readjoy_safe:
    lda buttons2
    sta last_frame_buttons2
    lda buttons1
    sta last_frame_buttons1
    ; Read the controllers once and stash the result
    jsr readjoy
    lda buttons2
    sta first_read_buttons2
    lda buttons1
    sta first_read_buttons1
    ; Read the controllers again and compare
    jsr readjoy
    ldx #1
cleanup_loop:
    ; Ignore read values if a bit deletion occurred
    lda buttons1,x
    cmp first_read_buttons1,x
    beq not_glitched
        lda last_frame_buttons,x
        sta buttons1,x
    not_glitched:
    dex
    bpl cleanup_loop
    rts
</pre>
:In november 2023 it was demonstrated that this is still subject to DPCM errors because the readjoy loop does not complete fast enough (allowing 2 matching corruptions of the same controller). So, aside from the compromise of 1 frame of lag, it wasn't completely DPCM error free either. Note that tepples has since replaced this code with the OAMDMA sync solution in his NROM template ([https://github.com/pinobatch/nrom-template/commit/5656fc285aaa92f34a9b56246362c145aeaef930 gitub: pinobatch/nrom-template changes]). So, perhaps this code may just be retired here for eternity. - [[User:Rainwarrior|Rainwarrior]] ([[User talk:Rainwarrior|talk]]) 00:27, 11 January 2024 (UTC)

Latest revision as of 00:27, 11 January 2024

Reorganization needed with Standard controller

See: Talk:Standard_controller#Reorganization_needed_with_Controller_Reading

Removed last-frame compromise

This code appeared in the DPCM Safety using Repeated Reads section. I have removed it, because I think it hurts comprehension for new readers who may not understand what they are trading away to save a few cycles they may not need. There's probably a place for this code somewhere, but I don't think it belongs in the middle of the article, and certainly not in lieu of a simpler and more standard example.

I left a description of the technique, but not the code. - Rainwarrior (talk) 13:14, 16 April 2019 (MDT)

Code:

last_frame_buttons1 = $00
last_frame_buttons2 = $01
first_read_buttons1 = $02
first_read_buttons2 = $03

readjoy_safe:
    lda buttons2
    sta last_frame_buttons2
    lda buttons1
    sta last_frame_buttons1

    ; Read the controllers once and stash the result
    jsr readjoy
    lda buttons2
    sta first_read_buttons2
    lda buttons1
    sta first_read_buttons1

    ; Read the controllers again and compare
    jsr readjoy
    ldx #1
cleanup_loop:
    ; Ignore read values if a bit deletion occurred
    lda buttons1,x
    cmp first_read_buttons1,x
    beq not_glitched
        lda last_frame_buttons,x
        sta buttons1,x
    not_glitched:

    dex
    bpl cleanup_loop

    rts
In november 2023 it was demonstrated that this is still subject to DPCM errors because the readjoy loop does not complete fast enough (allowing 2 matching corruptions of the same controller). So, aside from the compromise of 1 frame of lag, it wasn't completely DPCM error free either. Note that tepples has since replaced this code with the OAMDMA sync solution in his NROM template (gitub: pinobatch/nrom-template changes). So, perhaps this code may just be retired here for eternity. - Rainwarrior (talk) 00:27, 11 January 2024 (UTC)