What does 'Blitter off' really mean?

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mikro
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What does 'Blitter off' really mean?

Postby mikro » Thu Jul 26, 2018 8:15 pm

This may look like an obvious answer but to be honest, I can't really figure it out. For instance in Falcon, the register $ff8007 controls the Blitter. You can half its clock and you can enable/disable it. So what exactly happens if I disable it?

Please note, don't confuse this with the desktop settings found in earlier ST models - that checkbox disables hardware blitting in VDI (which is forced in Falcon's VDI).

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Re: What does 'Blitter off' really mean?

Postby Cyprian » Thu Jul 26, 2018 8:58 pm

which bit do you mean?

Code: Select all

-------+-----+-----------------------------------------------------+----------
$FF8007|byte |Falcon Bus Control                    BIT 5 . . 2 . 0|R/W (F030)
       |     |STe Bus Emulation (0 - on) ---------------'     |   ||
       |     |Blitter (0 - 8mhz, 1 - 16mhz) ------------------'   ||
       |     |68030 (0 - 8mhz, 1 - 16mhz) ------------------------'|


if it exists, it could e.g. turns on/off bus error when the CPU try to access the BLiTTER memory area
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Re: What does 'Blitter off' really mean?

Postby mikro » Thu Jul 26, 2018 9:16 pm

Cyprian wrote:which bit do you mean?

Yes, it's not in every registers list:

Code: Select all

$FFFF8007 [R/W] B         _65_32_0  System - Control
                           || || |
                           || || +- Prozessor-Takt
                           || ||    0 =  8 MHz
                           || ||    1 = 16 MHz
                           || |+--  BLiTTER-Takt
                           || |     0 =  8 MHz
                           || |     1 = 16 MHz
                           || +---  BLiTTER-Flag
                           ||       0 = BLiTTER An
                           ||       1 = BLiTTER Aus
                           |+-----  Umschaltung Bus-Mode
                           |        0 = STE
                           |        1 = Falcon
                           +------  RESET-Verhalten
                                    0 = immer Kaltstart
                                    1 = normal, "memvalid" wird
                                        beachtet

Also:

Code: Select all

$FFFF8006.W|RW|SYS_CTL|System Control              %MM______ _RS_bB_C |F
           |  |       | Monitor Type (M0,M1)--------++        || || | |F
           |  |       | Monochrome Monitor----------00        || || | |F
           |  |       | RGB Monitor-----------------01        || || | |F
           |  |       | VGA Monitor-----------------10        || || | |F
           |  |       | TV--------------------------11        || || | |F
           |  |       | Reset 0:ignore resetvector------------+| || | |F
           |  |       | STE-compatible-I/O 0:off,1:on----------+ || | |F
           |  |       | Blitterflag 0:on,1:off-------------------+| | |F
           |  |       | Blitterspeed 0:half clock,1:full clock----+ | |F
           |  |       | CPUspeed 0:half clock,1:full clock----------+ |F

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Re: What does 'Blitter off' really mean?

Postby ThorstenOtto » Fri Jul 27, 2018 1:07 am

mikro wrote:Yes, it's not in every registers list:
1 = normal, "memvalid" wird
beachtet


I don't know were you got that list from, but this looks rather strange. What does a piece of hardware have to do with the system-variable memvalid? I would think that these are more like bit registers that software can set and act accordingly, i can't imagine that the blitter suddenly reads that system variable on a reset.

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Re: What does 'Blitter off' really mean?

Postby mikro » Fri Jul 27, 2018 7:36 am

ThorstenOtto wrote:I don't know were you got that list from, but this looks rather strange. What does a piece of hardware have to do with the system-variable memvalid? I would think that these are more like bit registers that software can set and act accordingly, i can't imagine that the blitter suddenly reads that system variable on a reset.

Hey, you are the TOS expert here, RTFS (Sources ;-)). STARTUP.S indeed demonstrates how that bit is used. While looking into the sources I can't say anything about the Blitter on/off bit: it is enabled & set to 16 MHz but that's it. No mention about that specific bit at all.

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Re: What does 'Blitter off' really mean?

Postby ctirad » Fri Jul 27, 2018 8:38 am

From what i know the Blitter in F030 actually cannot be completeley switched off and the bit is just ignored.

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Re: What does 'Blitter off' really mean?

Postby ThorstenOtto » Fri Jul 27, 2018 9:27 am

mikro wrote:Hey, you are the TOS expert here


Oops, really? ;)

RTFS (Sources ;-))


Yes, but seeing that it is used somehow, and understanding why, when it is not documented anywhere are different things. I guess you actually have try it out and see what happens, eg. wether the blitter still accesses the bus when that bit is set.


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