Lpc2000

Gromann, Klaus wrote:

>attribute packed should help.
>But take care, the ARM7 processor can't access 32-bit wide to an address
>that is not 32-bit aligned.
>If you try to read 32 bit from the address 0x83000002, you don't get the
>expected result, but without any error message or exception.
>
>  
>

No, you cannot do that.  *THAT* is what is called "Alignment Fault" and 
an exception is thrown.

TomW


>Klaus
>
>-----Original Message-----
>From: lpc2000@yahoogroups.com [mailto:lpc2000@yahoogroups.com] On Behalf
>Of lehmannjluc
>Sent: Wednesday, November 09, 2005 11:55 AM
>To: lpc2000@yahoogroups.com
>Subject: [lpc2000] UBYTE alignment problem in structure
>
>
>I have the following structure definition: =========================
>#define PTR_ATTR                
>#define VPC3_PTR                PTR_ATTR *
>typedef struct
>{
>    UBYTE int_req1;
>    UBYTE int_req2;
>    union
>    {
>        struct
>        {
>            UBYTE int_reg1;
>            UBYTE int_reg2;
>            UBYTE status_L;
>            UBYTE status_H;
>        } (ULONG rd);
>        struct
>        {
>            UBYTE int_ack1;
>            UBYTE int_ack2;
>            UBYTE int_mask_L;
>            UBYTE int_mask_H;
>        } wr;
>    } isreg;
>    UBYTE mode_reg0_L;
>    //....and so on with various union and sub-structure.
>}  VPC3_STRUC;
>#define VPC3_STRUC_PTR    VPC3_STRUC    VPC3_PTR
>extern VPC3_STRUC_PTR     p_Vpc3;
>=========================
>This structure is used to point to a real hardware address.
>And the code is:
>=========================
>#define EM_START_ADDR_BANK3	(0x83000000)
>#define VPC3_ASIC_ADDRESS	(EM_START_ADDR_BANK3 + 0x0000)
>    p_Vpc3 = (VPC3_STRUC VPC3_PTR)VPC3_ASIC_ADDRESS;
>========================= But when we compile using the Ashling dev
>tools with GNU compiler 
>version 3.4.2 for a LPC2214 ARM, I have an alignment problem.
>&p_Vpc3->int_req1 points to 0x83000000 (which is correct) but whereas 
>I would expect &p_Vpc3->isreg.rd.int_reg1 to point to 0x83000002, it 
>points to 0x83000004 (same for &p_Vpc3->mode_reg0_L which points to 
>0x83000008 rather than the expected 0x83000006) and so on with the 
>following byte of the structure.  
>It looks like the compiler aligns the union on 32 bits, so drop an 
>empty 2 bytes after int_req2 element.
>I searched the archive for similar problem, but also I found some 
>alignment questions, none matched my problem or where even close.
>
>I am using a library supplied by the hardware chip manufacturer and I 
>cannot just rewrite the whole library.
>What could be done to force the compiler to point byte after byte and 
>not align to 32-bit ARM word ? If it can be done at all...
>
>Thanks in advance for any help you can provide,
>Jean-Luc Lehmann
>
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>Yahoo! Groups Links
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>Yahoo! Groups Links
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-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
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