Datasheet

Data Sheet ADAU1701
Rev. C | Page 37 of 52
2064 TO 2068 (0x0810 TO 0x0814)—SAFELOAD
DATA REGISTERS
Many applications require real-time microcontroller control of
signal processing parameters, such as filter coefficients, mixer
gains, multichannel virtualizing parameters, or dynamics
processing curves. When controlling a biquad filter, for
example, all of the parameters must be updated at the same
time. Doing so prevents the filter from executing with a mix of
old and new coefficients for one or two audio frames, thus
avoiding temporary instability and transients that may take a
long time to decay. To accomplish this, the ADAU1701 uses
safeload data registers to simultaneously load a set of five 28-bit
values to the desired parameter RAM address. Five registers are
used because a biquad filter uses five coefficients and, as
previously mentioned, it is desirable to do a complete update in
one transaction.
The first step in performing a safeload operation is writing the
parameter address to one of the safeload address registers (2069
to 2073). The 10-bit data-word to be written is the address in
parameter RAM to which the safeload is being performed. After
this address is written, the 28-bit data-word can be written to
the corresponding safeload data register (2064 to 2068).
The data formats for these writes are detailed in Table 29 and
Table 30. Table 38 shows how each of the five address registers
maps to its corresponding data register.
After the address and data registers are loaded, set the initiate
safeload transfer bit in the core control register to initiate the
loading into RAM. Each of the five safeload registers takes one of
the 1024 core instructions to load into the parameter RAM. The
total program lengths should, therefore, be limited to 1019 cycles
(1024 minus 5) to ensure that the SigmaDSP core always has at
least five cycles available. The safeload is guaranteed to occur
within one LRCLK period (21 μs for a f
S
of 48 kHz) of the initiate
safeload transfer bit being set.
The safeload logic automatically sends data to be loaded into
RAM from only those safeload registers that have been written
to since the last safeload operation. For example, if two parameters
are to be updated in the RAM, only two of the five safeload registers
must be written. When the initiate safeload transfer bit is asserted,
only data from those two registers are sent to the RAM; the other
three registers are not sent to the RAM and may hold old or
invalid data.
Table 38. Safeload Address and Data Register Mapping
Safeload
Register
Safeload
Address Register
Safeload
Data Register
0 2069 2064
1 2070 2065
2 2071 2066
3 2072 2067
4 2073 2068
Table 39. Safeload Registers Bit Map
D39 D38 D37 D36 D35 D34 D33 D32
D31 D30 D29 D28 D27 D26 D25 D24 D23 D22 D21 D20 D19 D18 D17 D16
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 Default
SD39 SD38 SD37 SD36 SD35 SD34 SD33 SD32 0x00
SD31 SD30 SD29 SD28 SD27 SD26 SD25 SD24 SD23 SD22 SD21 SD20 SD19 SD18 SD17 SD16 0x0000
SD15 SD14 SD13 SD12 SD11 SD10 SD09 SD08 SD07 SD06 SD05 SD04 SD03 SD02 SD01 SD00 0x0000
Table 40.
Bit Name Description
SD[39:0]
Safeload Data. Data (program, parameters, register contents) to be loaded into the RAMs or
registers.
2069 TO 2073 (0x0815 TO 0x819)—SAFELOAD ADDRESS REGISTERS
Table 41. Safeload Address Registers Bit Map
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 Default
0 0 0 0 SA11 SA10 SA09 SA08 SA07 SA06 SA05 SA04 SA03 SA02 SA01 SA00 0x0000
Table 42.
Bit Name Description
SA[11:0] Safeload Address. Address of data that is to be loaded into the RAMs or registers