From:	"Simon" <simonhch AT yahoo DOT com DOT tw>
To:	<djgpp AT delorie DOT com>
Subject:	Using UDMA with DJGPP
Date:	Thu, 26 Jun 2003 10:52:40 +0800
Message-ID:	<000201c33b8e$136f1e30$2810a8c0@epo.com.tw>
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Sorry, Email again...

I want to use UDMA, but I don't know how to get the physical address of
the buffer I allocate for that purpose

 For BCC code fragment :

//  Builds the PRD table for the given buffer address and size
int build_PRD_table(unsigned int far *buffer, unsigned long size)
{
    register unsigned long linear_address = ((unsigned
long)FP_SEG(buffer) << 4) + FP_OFF(buffer);
    register unsigned long residual_size = size;
    unsigned long int temp_size;

	// Use 2's complement to caculate
    if ((temp_size = (-linear_address) & 0x0000FFFFL) == 0)
        temp_size = 0x10000L;                                 

    PRD_table[0].base_addr = linear_address;
    PRD_used = 1;

    if (residual_size <= temp_size)     // one PRD is enough?
    {
        PRD_table[0].byte_count = residual_size;
        PRD_table[0].eot = 0x8000;
        return(1);
    }
    else
    {
        PRD_table[0].eot = 0;
        PRD_table[0].byte_count = temp_size;
        linear_address += temp_size;
        residual_size -= temp_size;
    }

    while (residual_size > 0x10000L)
    {
        PRD_table[PRD_used].base_addr = linear_address;
        PRD_table[PRD_used].byte_count = 0;         // 0 idicates 64K
bytes
        PRD_table[PRD_used++].eot = 0;
        linear_address += 0x10000L;
        residual_size  -= 0x10000L;
    }
    PRD_table[PRD_used].base_addr = linear_address;
    PRD_table[PRD_used].byte_count = residual_size;
    PRD_table[PRD_used++].eot = 0x8000;
    return(1);
}

How to get linear_address ?
DJGPP not support FP_SEG() and FP_OFF() macro.

Thanks your help.

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