Parallel Port Throughput
8-14
ADSP-2126x SHARC Processor Hardware Reference
8-Bit Access
In 8-bit mode, the first data-access (whether a read or a write) always con-
sists of one
ALE
cycle followed by four data cycles. As long as the upper 16
bits of address do not change, each subsequent transfer consists of four
data cycles. The
ALE
cycle is inserted only when the parallel port address
crosses an 8-bit boundary page, in other words, after every 256 bytes that
are transferred.
For example, if
PPDUR3
,
BHC
= 0, and the processor is in 8-bit mode. The
first byte on a new page takes six core cycles (three for the
ALE
cycle and
three for the data cycle), and the next sequential 255 bytes consume three
core cycles each.
Therefore, the average data rate for a 256 byte page is:
(3
CCLK
x 255 + 6
CCLK
x 1) / 256 = 3.01 core clock cycles per byte.
For a 200 MHz core, this results in:
(200M
CCLK
/sec) x (1 byte/3.008
CCLK
) = 66.4M bytes/sec
16-Bit Access
In 16-bit mode, every word transfer consists of two
ALE
cycles and two
data cycles. Therefore, for every 32-bit word transferred, at least six
CCLK
cycles are needed to transfer the data plus an additional six
CCLK
cycles for
the two
ALE
cycles, for a total of 12
CCLK
cycles per 32-bit transfer (four
bytes). For a 200 MHz core clock, this results in a maximum sustained
data rate device of:
200 MHz /12 = 16.67 Million 32-bit words/sec = 66.6M Bytes/sec
There is a specific case which allows this maximum rate to be exceeded. If
the external address modifier (
EMPP
) is set to a stride of zero, then only one
Summary of Contents for ADSP-21261 SHARC
Page 30: ...Contents xxx ADSP 2126x SHARC Processor Hardware Reference ...
Page 40: ...Register Diagram Conventions xl ADSP 2126x SHARC Processor Hardware Reference ...
Page 58: ...Differences From Previous SHARCs 1 18 ADSP 2126x SHARC Processor Hardware Reference ...
Page 112: ...Secondary Processing Element PEy 2 54 ADSP 2126x SHARC Processor Hardware Reference ...
Page 178: ...Summary 3 66 ADSP 2126x SHARC Processor Hardware Reference ...
Page 204: ...DAG Instruction Summary 4 26 ADSP 2126x SHARC Processor Hardware Reference ...
Page 322: ...Setting Up DMA 7 32 ADSP 2126x SHARC Processor Hardware Reference ...
Page 436: ...SPORT Programming Examples 9 86 ADSP 2126x SHARC Processor Hardware Reference ...
Page 521: ...ADSP 2126x SHARC Processor Hardware Reference 11 31 Input Data Port rts IDP_ISR end ...
Page 522: ...Input Data Port Programming Example 11 32 ADSP 2126x SHARC Processor Hardware Reference ...
Page 590: ...Timer Programming Examples 14 20 ADSP 2126x SHARC Processor Hardware Reference ...
Page 796: ...I O Processor Registers A 174 ADSP 2126x SHARC Processor Hardware Reference ...
Page 800: ...B 4 ADSP 2126x SHARC Processor Core Manual ...
Page 846: ...Index I 36 ADSP 2126x SHARC Processor Hardware Reference ...