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RAM Poke Problem

Forum Index -> ZBasic Native Mode

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mikep

Joined: 24 Sep 2005
Posts: 765
Location: Austin, TX

Posted: 14 July 2008, 1:18 AM Post subject: RAM Poke Problem

Here is a test program:

Code:

Private msgbuf(1 To 64) as Byte
Private bufEnd as UnsignedInteger

Public Sub Main()
bufEnd = msgbuf.DataAddress
Debug.Print CStrHex(bufEnd); " "; cstrhex(msgbuf.DataAddress)
Call RAMPoke(&hD7, bufEnd)
Call RAMPoke(&h11, bufEnd+1)
Debug.Print CStrHex(bufEnd); " "; cstrhex(msgbuf.DataAddress); " "; CStrHex(RAMPeekWord(bufEnd))

bufEnd = msgbuf.DataAddress
Debug.Print CStrHex(bufEnd); " "; cstrhex(msgbuf.DataAddress)
Call RAMPokeWord(&h11D7, bufEnd)
Debug.Print CStrHex(bufEnd); " "; cstrhex(msgbuf.DataAddress); " "; CStrHex(RAMPeekWord(bufEnd))
End Sub

On a ZX24 the output is correct

Code:

00a0 00a0
00a0 00a0 11d7
00a0 00a0
00a0 00a0 11d7

On a ZX-24n it appears to poke the value into the variable rather than the address where the variable is pointing to

Code:

0102 0102
01d7 0102 1100
0102 0102
11d7 0102 1100

mikep

Joined: 24 Sep 2005
Posts: 765
Location: Austin, TX

Posted: 14 July 2008, 1:34 AM Post subject: Re: RAM Poke Problem

mikep wrote:

Call RAMPokeWord(&h11D7, bufEnd)

The generated code is

Code:

*(uint16_t *)&zv_bufEnd = 4567;

rather than

Code:

*(uint16_t *)zv_bufEnd = 4567;

dkinzer
Site Admin

Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR

Posted: 14 July 2008, 2:21 AM Post subject: Re: RAM Poke Problem

mikep wrote:

On a ZX-24n it appears to poke the value into the variable rather than the address where the variable is pointing to

Thanks. It is interesting that the address/dereferencing code generated for RamPeek() is correct. Somehow we missed the problem for RamPoke(). A solution to the problem has been identified and tested preliminarily.

One way to work around the problem is to use a based variable:

Code:

Dim msgWord as UnsignedInteger Based msgBuf.DataAddress
msgWord = &H11D7

If you need to populate several elements of msgBuf, you can use an auxiliary variable:

Code:

Dim addr as UnsignedInteger
Dim msgWord as UnsignedInteger Based addr
addr = msgBuf.DataAddr
msgWord = &H11D7

A third option that may be useful if the message buffer lends itself to being described by a structure is to define a structure matching the message and then define a structure variable based on the address of the message buffer.

mikep

Joined: 24 Sep 2005
Posts: 765
Location: Austin, TX

Posted: 14 July 2008, 3:41 AM Post subject: Re: RAM Poke Problem

dkinzer wrote:

[It is interesting that the address/dereferencing code generated for RamPeek() is correct. Somehow we missed the problem for RamPoke(). A solution to the problem has been identified and tested preliminarily.

Just to point out that all 3 variations have the problem.

dkinzer wrote:

One way to work around the problem is to use a based variable:

Code:

Dim msgWord as UnsignedInteger Based msgBuf.DataAddress
msgWord = &H11D7

If you need to populate several elements of msgBuf, you can use an auxiliary variable:

As it turns out I already had the auxillary variable. Here is my code with the work around:

Code:

#if Option.TargetCode="ZVM"
      Call RAMPoke(CByte(length), bufend)
      bufEnd = bufEnd + 1
      Call RAMPokeWord(sequenceNumber, bufEnd)
#else
      Dim msgWord as UnsignedInteger Based bufend
      Dim msgByte as Byte Based bufend
      msgByte = CByte(length)
      bufend = bufend + 1
      msgWord = sequenceNumber
#endif
      bufEnd = bufEnd + 2

dkinzer
Site Admin

Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR

Posted: 14 July 2008, 5:02 AM Post subject: Re: RAM Poke Problem

mikep wrote:

Just to point out that all 3 variations have the problem.

Yes, they use common code since the only difference is the type of the cast. Consequently, the correction fixed all three.

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