10
Memory Interface
10 – 15
10.4
BOOT MEMORY INTERFACE
This section describes the boot memory interface of all ADSP-21xx
processors except the ADSP-2181.
The entire internal program memory, or any portion of it, can be loaded
from an external source using a boot sequence. To interface with
inexpensive EPROM, the processor loads instructions one byte at a time.
Automatic booting at reset depends on the state of the MMAP pin at the
time of processor reset. The boot sequence occurs if the MMAP pin is 0.
The boot sequence can also be initiated after reset by software.
The ADSP-2111, ADSP-2171, and ADSP-21msp5x processors, which
include a Host Interface Port (HIP), can boot using either the memory
interface or the HIP (from a host computer). The state of the BMODE pin
determines which method is used: the memory interface if BMODE=0, or
the HIP if BMODE=1. Booting through the HIP is described in Chapter 7.
BR
is recognized during the booting sequence. The bus is granted after
completion of loading the current byte.
The ADSP-216x contain on-chip program memory ROM; on these devices,
no booting occurs.
10.4.1 Boot Pages
Boot memory is organized into eight pages, each of which can be 8K bytes
long. Every fourth byte of a page is an “empty” byte, except the first one,
which contains the page length. Each set of three bytes between successive
empty bytes contains an instruction. The page length is read first and then
bytes are loaded from the top of the page downwards. This results in
shorter booting times for shorter pages.
The length of the boot page is given as:
page length = (number of 24-bit PM words / 8) – 1
That is, a page length of 0 causes the boot address generator to generate
byte addresses for 8 words which reside in 32 sequential ROM locations.
The PROM Splitter utility, part of the ADSP-2100 Family Development
Software tools, calculates the proper page length for your program and
orders the bytes of your program as shown in Figure 10.16 (on the next
page).