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Question about variables across cogs / across spin and assembly — Parallax Forums

Question about variables across cogs / across spin and assembly

smbakersmbaker Posts: 164
in PASM/Spin (P1)

Hi, it's been a long time since my last propeller project, and I've forgot quite a bit. Lately I was trying to hack the maccasoft VGA serial terminal, adding the ability to strip the MSB from incoming characters.

My question is here in my fork: https://github.com/sbelectronics/prop_ser_term/blob/ae8f5034cd4aa27d5ca89f457e7fe05d361e3672/src/terminal.spin#L588

I tried to set a variable called mode7bit. Setting this variable works fine if done prior to initializing the vt100 cog (see line 225 for a working example). I'm reading this variable from line 890 using rdbyte which I understand reads from hub memory. So it seems to me the change should work fine from one cog to another.

This terminal does make use of "overlays" which is a technique that I didn't use back during my active propeller years, so I'm not sure if there's something I'm just not understanding.

Anyhow, can any spin or pasm experts spot where my problem is? Simply hitting the reset button after changing my settings is fine, but it would be nice to understand what the issue is.

Also, where have all the prop folks gone? I remember this place as being bustling with activity, but I don't see many of the familiar faces.

Thanks,
Scott

Comments

  • Wuerfel_21Wuerfel_21 Posts: 4,664

    mode7bit is defined as an initialized cog register. So you can change its initial value before you launch the cog by assigning to it. When the cog is launched it gets copied into that cog's cog RAM with whatever value it has at the time.

                        rdbyte  t1, mode7bit

    This is not how RDBYTE works. What this will do is read a byte from hub memory at the address stored in mode7bit (in your case 0000 or 0001). The reason this appears to work is because the first bytes in hub are normally 00 B4 C4 04 (because clkfreq is usually 80000000), so reading a byte from address zero will actually return zero.

    If you want this to work, you can set mode7bit := @mode7bit before starting, though that'll confuse people reading the code :P

  • smbakersmbaker Posts: 164

    Thanks, this makes a lot of sense!

  • evanhevanh Posts: 15,380
    edited 2024-07-08 06:52

    @smbaker said:
    Also, where have all the prop folks gone? I remember this place as being bustling with activity, but I don't see many of the familiar faces.

    Some will be waiting for the Prop2 docs to be fleshed out before diving in on that.
    Many of the talkers possibly have moved on to other pastures. RaspberryPi likely clean out a lot of 'em over the years. And a number have died of old age too.
    There is new names showing up still.

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