blocks|key|3503536|text|这是正确的；如果您使用for+...'address+use覆盖特定地址处的对象，则以后无法更改它。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3503537|一般来说，我会尽量避免重叠。你所展示的对他们来说是一个缺点。另一种是，如果对象有任何需要初始化的部分，它们将在每次对象细化时重新初始化。|3503538|不过，有一件事我必须事先问一问:这看起来像一个设备驱动程序。如果你不喜欢访问PCI总线的结果，那也没问题。当然，解决问题的明显方法是将对象读取到一个临时变量中，并在不想访问PCI总线时使用它。但很明显，当您这样做时，您不再直接从设备读取数据，因此看不到它对其内存映射寄存器所做的更改(并且您的更改不会直接传递到这些内存映射寄存器)。这就是你想要的，对吧？Ada不包含允许您在不命中PCI总线的情况下将数据进出PCI总线的魔术。|3503539|看起来你好像在想这一行：|3503540|for+NextPacketRegister'Address+use+To_Address+(16#A000_0000#+%2B+Integer_Address+(PacketBufferPointer));|3503541|意思是：“每次我访问NextPacketRegister时，找到PacketBufferPointer的值并将其覆盖到它现在所在的位置”。事实并非如此。当你的声明被处理时，这只会发生一次。此后，每次访问类似NextPacketRegister[12]的内容都将转到同一位置，而不访问任何PacketBufferPointer。|BOLD|3503542|另一种方法是使用指针和Unchecked_Conversion。这通常是我首选的覆盖解决方案。它看起来毛发更多，但你正在做的是毛发，所以它应该看起来是这样的。而且，它不会对覆盖的内存区执行初始化。我想这可能是一件坏事，如果你指望这些的话。当然，如果您愿意，以这种方式覆盖可能会导致对PacketBufferPointer的访问。你可以根据你的编码方式来控制它。|3503543|既然您问到了指针，在这种情况下，我认为您有一个非常有效的用例来使用包System.Address_to_Access_Conversions。我手头没有编译器，但我认为它应该是这样的：|3503544|type+Next_Packet_Array+is+array+(1+..+Natural+(Size))+of+Unsigned_32;
package+Next_Packet_Array_Convert+is+new+System.Address_To_Access_Conversions
+++(Next_Packet_Array);
Synced_Next_Packet_Address+:+System.Address;|code-block|syntax|javascript|3503545|现在，当你“同步”的时候，我猜你会想要点击那个PacketBufferPointer来获得寄存器值(作为一个SYSTEM.ADDRESS)，并将它保存到一个变量中以备后用：|3503546|Synced_Next_Packet_Address+=+16#A000_0000#+%2B+Integer_Address+(PacketBufferPointer);|3503547|当您想要访问Next_Packet_Array时，应该是这样的：Next_Packet_Array_Convert.To_Pointer+(Synced_Next_Packet_Address).all|3503548|entityMap|0|LINK|mutability|MUTABLE|url|http://www.adaic.org/standards/95lrm/html/RM-13-7-2.html#I4349^0|B|J|0|0|0|0|0|2U|0|2L|1Y|2V|M|3Z|J|0|0|50|3X|J|0|0|2K|Y|10|0|0|0|0|2E|0|0|0|2T|W|1X|0^^$0|@$1|2|3|4|5|6|7|1D|8|@$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1G|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|1H|8|@]|D|@]|E|$]]|$1|J|3|K|5|6|7|1I|8|@]|D|@]|E|$]]|$1|L|3|M|5|6|7|1J|8|@$9|1K|A|1L|B|C]]|D|@]|E|$]]|$1|N|3|O|5|6|7|1M|8|@$9|1N|A|1O|B|P]|$9|1P|A|1Q|B|C]|$9|1R|A|1S|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|6|7|1T|8|@$9|1U|A|1V|B|P]|$9|1W|A|1X|B|C]]|D|@]|E|$]]|$1|S|3|T|5|6|7|1Y|8|@$9|1Z|A|20|B|P]]|D|@$9|21|A|22|1|23]]|E|$]]|$1|U|3|V|5|W|7|24|8|@]|D|@]|E|$X|Y]]|$1|Z|3|10|5|6|7|25|8|@$9|26|A|27|B|P]]|D|@]|E|$]]|$1|11|3|12|5|W|7|28|8|@]|D|@]|E|$X|Y]]|$1|13|3|14|5|6|7|29|8|@$9|2A|A|2B|B|P]|$9|2C|A|2D|B|C]]|D|@]|E|$]]|$1|15|3|-4|5|6|7|2E|8|@]|D|@]|E|$]]]|16|$17|$5|18|19|1A|E|$1B|1C]]]]

That is correct; if you use <code>for ...'address use</code> to overlay an object at a specific address, you cannot change it later.

Generally I try to avoid overlays. What you show is one drawback to them. Another is that if the object has any parts that require initialization, they will be reinitialized every time the object is elaborated.

One thing I do have to ask up front though: This looks like a device driver. If you don't like the hit from going to the PCI bus then, fine. The obvious way around your problem of course is to just read the object into a temporary variable and use that when you don't want to hit the PCI bus. But obviously when you do that you are no longer reading directly from the device, and thus won't see changes it made to its memory-mapped registers (and your changes won't go straight to those memory-mapped registers). That's what you want, right? Ada contains no magic to allow you to get data on and off the PCI bus without hitting the PCI bus.

It almost looks like you are thinking that this line:

<code>for NextPacketRegister'Address use To_Address (16#A000_0000# + Integer_Address (PacketBufferPointer));</code>

Means: "Every time I access NextPacketRegister, go find the value of PacketBufferPointer and overlay it where it happens to be right now". That is not the case. This will only happen once when your declaration is processed. Thereafter, every access to something like <code>NextPacketRegister[12]</code> will go to the same place, without any access to <code>PacketBufferPointer</code>.

Another way would be to use pointers and Unchecked_Conversion. That's generally my preferred solution for overlays. It looks hairer, but what you are doing is hairy, so it should look that way. Also, it doesn't perform initializations on the overlaid memory area. I suppose that could be a bad thing though, if you count on those. Of course overlaying this way could cause an access to <code>PacketBufferPointer</code>, if you want. You'd have control over it depending on how you code it.

Since you asked about pointers, in this case I think you have a very valid case for using the package <a href="http://www.adaic.org/standards/95lrm/html/RM-13-7-2.html#I4349" rel="nofollow">System.Address_to_Access_Conversions</a>. I don't have the compiler handy, but I think it would go something like this:

<pre><code>type Next_Packet_Array is array (1 .. Natural (Size)) of Unsigned_32;
package Next_Packet_Array_Convert is new System.Address_To_Access_Conversions
 (Next_Packet_Array);
Synced_Next_Packet_Address : System.Address;
</code></pre>

Now when you "sync", I guess you'd want to hit that PacketBufferPointer to get the register value (as a SYSTEM.ADDRESS), and save it into a variable for later use:

<pre><code>Synced_Next_Packet_Address = 16#A000_0000# + Integer_Address (PacketBufferPointer);
</code></pre>

And when you want to access the Next_Packet_Array, it would be something like this: <code>Next_Packet_Array_Convert.To_Pointer (Synced_Next_Packet_Address).all</code>

blocks|key|2018115|text|创建一个结构(缓冲区数组？)这就是您的数据包缓冲区集的外观，并将其放在数组开始处的地址。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2018116|从寄存器中读取数组索引。|2018117|你可以用任何语言写C，甚至是Ada。|2018118|至少它可以工作，并且你得到了一些合理的边界检查。|2018119|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

Make a structure (array of buffers ? ) that is what your set of packet buffers looks like and sit that at the address of the start of the array.

read the array index from the register.

you can write C in any language, even Ada.

At least it works and you get some sensible bounds checks.

I have an array and a variable declared like this

<pre><code>NextPacketRegister : array (1 .. Natural (Size)) of Unsigned_32; 
PacketBufferPointer : Unsigned_32; 

for PacketBufferPointer'Address use To_Address (SPW_PORT_0_OUT_REG_ADDR);

for NextPacketRegister'Address use To_Address (16#A000_0000# + Integer_Address (PacketBufferPointer));
</code></pre>

PacketBufferPointer points to an HW registers that you access thru the PCI of our board.
NextPacketRegister uses this register's value + 16#A000_0000#

The thing is everytime I access NextPacketRegister, behind the scene I perform a PCI access, these access are very slow and we are trying to remove this limitation.

But I can't seem to find a way to modify NextPacketRegister'Address during runtime (I'd like to read ONCE the PacketBufferPointer register and then add this value + 16#A000_0000# only once so I don't have to perform PCI access everytime.

I looked around but I have no clue how I could achieve this.

Ada Modifying a variable address during runtime

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有一个数组和一个变量，声明如下NextPacketRegister     : array (1 .. Natural (Size)) of Unsigned_32;  PacketBufferPointer    : Unsigned_32;  for PacketBufferPointer'Address use...

问Ada在运行时修改变量地址
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