Analog Devices ee-78 Application Notes

Engineer To Engineer Note EE-78

Technical Notes on using Analog Devices’ DSP components and development tools

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BDMA Usage on 100 pin ADSP-218x DSPs configured for IDMA use.

The 100 pin versions of the ADSP-218x processors can be configured to either fully support the IDMA
interface of a memory interface. When these components are configured to utilize the IDMA interface, the
memory interface is only partially functional. This allows only limited usage for the memory interfaces. The
BDMA interface can still be used in this mode, albeit in a somewhat limited way.

This document will show how to set up BDMA in IDMA mode with the following features.

• 20 Bits of BMDA address space.

• Approx. 8 cycles overhead per DM or PM word transferred in blocks of up to 256 DM words or

170 PM words.

• Supports both reading and writing of BM.

This document will show example source code demonstrating the use of BDMA on the ADSP-2185 in IDMA
mode. This code is shown at the end of this document.

In this mode of operation the processor only normally provides 1 address bit. This does not make it impossible
to use the BDMA functions. Up to 20 bits of address can be generated for use with the BDMA function. The
approach used in this document creates and address for BDMA in the following way:

Pin name fl2 fl1 fl0 pf7:0 d23:16 a0
Number of bits 3 8 8 1

This creates an address of up to 20 bits which can address 1 Megabyte. The different sections of the address
need to be updated manually, but a trick in setting up the transfers allows the d23:16 section of the address to
automatically be updated. By setting the BEAD register to all ones for the bits which are not used causes an
automatic carry into the BMPAGE register. This allows the one, two, or three transfers needed to transfer an
internal memory word to be done as a single BDMA transfer.

The example code is structured to set up a block transfer of up to 256 words for DM and 170 words for PM.
The blocks are transferred at a rate of one DM or PM word per BDMA interrupt. The interrupt routine
automatically sets up the next word for transfer. The block size is limited due to the fact that the code shown
does not update either the pf7:0 pins or the fl2:0 pins. The problem is basically that a single DM or PM word
which would cross a 512 byte boundary set by the number of bits automatically updated by the BDMA

a

interface would require the update the other address fields. There is a tradeoff between supporting larger blocks
and overhead. This example shows a bias toward limiting overhead at a cost of additional limitations.

The code has three parts, the main program, a block transfer setup subroutine, and the BDMA interrupt
handler. The main program creates a small DM buffer full of data and then uses the block transfer subroutine to
copy it out to BM. It then reads it back from the BM to a small buffer in DM. It then copies the first 100 words
of PM (itself) to BM. The main program polls the number of remaining words in each transfer to determine
when to continue. The main program would be available do other tasks at these waiting points.

The block transfer subroutine “hokeyb” is used to set up the BMDA control registers and the address bits to
cause the requested transfer.

The BDMA interrupt routine does the necessary adjustments to the control words, decrements the block count,
and triggers the next transfer. It could also call a user BDMA subroutine when the block is finished.

{ --------------------------------------------------------

Show an example of BDMA on IDMA configured part

uses address bus made up of:
fl0, pf7:0, d23:16, a0

transfers multiple dm or pm words to/from bm with
one word transferred per BDMA interrupt. This version
does not automatically update pf7:0 or fl0.

Date: May 16, 1997

---------------------------------------------------------- }

.module/ram/abs=0 hokey;

.var/dm/ram hbwords;

jump START; nop; nop; nop; {0x0000 reset}
rti; nop; nop; nop; {0x0004 irq2}
rti; nop; nop; nop; {0x0008 irql1}
rti; nop; nop; nop; {0x000c irql0}
rti; nop; nop; nop; {0x0010 sp0tx}
rti; nop; nop; nop; {0x0014 sp0rx}
rti; nop; nop; nop; {0x0018 irqe}
jump BDMAINT; nop; nop; nop; {0x001c bmda}
rti; nop; nop; nop; {0x0020 sp1tx/nirq1}

EE-78 Page 2

Notes on using Analog Devices’ DSP components and development tools

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rti; nop; nop; nop; {0x0024 sp1rx/nirq0}
rti; nop; nop; nop; {0x0028 timer}
rti; nop; nop; nop; {0x002c pwd}

#define ENABDMA 0x8
#define CLRBDMA 0x8

START:
{ Set wait states to 0 for PM and 0 for DM }

icntl=0x03;

ax0=CLRBDMA; {clear bmda interrupt if left over from booting}
ifc=ax0;

ax0=0x1bff; {1 bdma waitstate, cms normal, pfs=output}
dm(0x3fe6)=ax0;

imask=ENABDMA; {unmask bdma interrupt}

{main code begins here}
i0=0x3000;
m0=1;
l0=0;

my0=0x4321; {initialize dm with a pattern}
cntr=24;
do loopy until ce;
mx0=cntr;
mr=mx0*my0(ss);
loopy: dm(i0,m0)=mr0;

{ set up first transfer (write of dm to bm)}
ax0=0x3000; {set biad}
dm(0x3fe1)=ax0;

ax0=24; {number of words}
dm(hbwords)=ax0;

ay0=0x05; {direction and mode}
si=0x0; {address lsb's}
ax0=0x0000; {address msb's}

call hokeyb; {do the transfer}

EE-78 Page 3

Notes on using Analog Devices’ DSP components and development tools

Phone: (800) ANALOG-D, FAX: [phone], FTP: ftp.analog.com, EMAIL: [e-mail]