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Register.PersistentSize et al as compile-time constants

 
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stevech



Joined: 23 Feb 2006
Posts: 657
Posted: 01 November 2006, 3:38 AM    Post subject: Register.PersistentSize et al as compile-time constants Reply with quote
Correct? ...

Things like

Register.PersistentSize

could be but aren't evaluated at compile-time.

Thus, I must keep my #if and const defs so as to be usable for DIM.
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dkinzer
Site Admin


Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
Posted: 01 November 2006, 3:48 AM    Post subject: Re: Register.PersistentSize et al as compile-time constants Reply with quote
stevech wrote:
Register.PersistentSize could be but [isn't] evaluated at compile-time.

Register.PersistentSize is constant at compile-time evidenced by this listing:
Code:
           Sub Main()
               ps = Register.PersistentSize
0014 1be003      PSHI_W         0x03e0 (992)
0017 21a000      POPA_W         0x00a0 (160)
            End Sub
001a 06          RET

You are correct, however, that the compiler doesn't treat it like a constant for the purposes that you mentioned. It probably should.
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stevech



Joined: 23 Feb 2006
Posts: 657
Posted: 01 November 2006, 3:56 AM    Post subject: Reply with quote
like

const PMsize = Register.PersistentSize

...
...

const infoMax = (PMsize - N) \ sizeof(MyType)

or

DIM info(PMSize - M) as BYTE
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dkinzer
Site Admin


Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
Posted: 01 November 2006, 4:15 AM    Post subject: Reply with quote
Understood. I probably should have thought of that. I've modified the tables to make some of the Register.xxx items look like constants. In particular,

Register.RamStart
Register.PersistentStart
Register.PersistentSize

I can't also make Register.RamSize constant because of the possibility of the presence of external RAM on future ZX models. It may be possible to have it be a constant for targets that have a constant RAM size and be a read-only variable for others. That may cause more confusion than it's worth, though.
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stevech



Joined: 23 Feb 2006
Posts: 657
Posted: 01 November 2006, 5:01 AM    Post subject: Reply with quote
sounds good.

Register.PersistentSize

would be a constant? For any given VM release, I suppose.
or perhaps it's the size of the chip's EEPROM, excluding the portion used by the VM.
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dkinzer
Site Admin


Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
Posted: 01 November 2006, 6:18 AM    Post subject: Reply with quote
stevech wrote:
perhaps it's the size of the chip's EEPROM, excluding the portion used by the VM.

That is correct. A section is reserved for system use; most of it unused at present.
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stevech



Joined: 23 Feb 2006
Posts: 657
Posted: 01 November 2006, 6:21 AM    Post subject: Reply with quote
while you're twiddling, maybe a constant or run-time to discover how much of the persistent EEPROM area is reserved, given this region begins at zero.
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dkinzer
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Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
Posted: 01 November 2006, 16:11 PM    Post subject: Reply with quote
stevech wrote:
while you're twiddling, maybe a constant or run-time to discover how much of the persistent EEPROM area is reserved, given this region begins at zero.

That is available, by implication, in Register.PersistentStart. Currently, Register.PersistentSize will always have the value 32, implying that the first 32 bytes are reserved for system use. For the mega32-based ZX devices, Register.PersistentSize will be 992. The sum of these two is the total number of bytes of internal EEPROM.

Register.PersistentSize - Register.PersistentUsed gives the number of unused bytes of Persistent Memory in the user portion of the internal EEPROM and Register.PersistentStart + Register.PersistentUsed gives the address of the first unused byte.

I believe that these three values completely describe the allocation of the PersistentMemory resource.
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stevech



Joined: 23 Feb 2006
Posts: 657
Posted: 02 November 2006, 0:52 AM    Post subject: Reply with quote
ah, got it. Those are too new to be in the docs yet.
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dkinzer
Site Admin


Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
Posted: 02 November 2006, 1:53 AM    Post subject: Reply with quote
stevech wrote:
ah, got it. Those are too new to be in the docs yet.

That's true. However, the meaning of each is the same as the similarly named values for RAM.
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