CS493002-CL Cirrus Logic, CS493002-CL Datasheet - Page 64

• Manufacturer Part Number: CS493002-CL
• Description: Multi-Standard Audio Decoder Family
• Manufacturer: Cirrus Logic

external ROM, in order to have access to the single
application code stored in the 32 kilobyte non-
paged memory. The host is completely isolated
from memory accesses in this situation. Once the
hardware has been designed, the DSP itself will be
responsible for all communication with the ROM.
8.7.2. 32 Kilobyte Paged Autoboot Memory
An external memory architecture which is paged
on 32 Kilobyte boundaries offers the higher end
system the ability to store several full download or
IBA application codes in each 32 Kilobyte page.
Figure 41 shows an example of a 32 Kilobyte
paged memory image for a the premium 6.1/7.1
channel system describe in Table 12 above.
The flow diagram given in Figure 36 demonstrates
the interaction required by the microcontroller
during autoboot. After placing the decoder into a
reset state, the host selects the page in memory
containing first code by driving uC15 to a low state.
The host also drives ABOOT low and holds it in a
low state until the rising edge of RESET to initiate
autoboot. As noted in the autoboot section, the
ABOOT pin should be connected to an open-drain
output of the microcontroller so as to allow the
specified pull-up resistor to generate the high
value. The open-drain driver is required because
the DSP will begin using the pin as an output after
a successful download (INTREQ and ABOOT are
multiplexed on the same pin).
After waiting for 175 ms, the download should
have completed. During the wait period, the host
should ignore all INTREQ behavior (mask the
INTREQ interrupt). The host can then verify that
the code has successfully initialized itself by
reading a variable from the application and
64
Figure 40. Non-Paged Memory
0x00000
0x0FF FF
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or
checking the returned value against the default
value. Any variable can be used for the verification
step, but a robust design will select a variable
whose value is neither all 0’s nor all 1’s. If the first
read attempt returns an incorrect value, a 5 ms wait
should be inserted and the read should be repeated.
If a second invalid number is read, the entire boot
process should be repeated. When the number
returned matches the default value for the variable
read, the host knows that the application is resident
in the DSP and awaiting further instruction. Please
see Section 8.2, “Autoboot” on page 56 for more
information.
For systems that would prefer to store all
application codes in an external parallel Flash
Memory (vs. a OTP EPROM) in order to realize a
“field-upgradable”
[e-mail] for information
Figure 41. Example Contents of a Paged 32 Kilobytes
External Memory (Total 256 Kilobytes)
0x07FFF
0x0FFFF
0x17FFF
0x1FFFF
0x27FFF
0x2FFFF
0x37FFF
0x3FFFF
0x00000
0x08000
0x10000
0x18000
0x20000
0x28000
0x30000
0x38000
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