UAC 3552A
PRELIMINARY DATA SHEET
2. Functional Description
2.1. Hardware
The ROM contains the USB drivers for the microcon-
troller as well as the complete descriptor table includ-
ing the report descriptor for the HID-class. Some parts
of the descriptor which are subjected to be changed by
the customer, however, reside in the EEPROM.
A detailed block diagram of the UAC 3552A is depicted
in Fig. 2–1. The functions of the blocks are explained
in the following sections.
The EEPROM is built to keep static customer-related
data that will customize the UAC 3552A-based USB
device during production.
2.1.1. USB Interface
2.1.1.1. Transceiver
The 128×8 bit EEPROM contains the customer spe-
cific information of the USB device descriptor, like ven-
dor ID, product ID, as well as strings for manufacturer,
product and serial number. Apart from this USB-
related information, the EEPROM holds customer-spe-
cific parameters for the PerfectSpeaker equalizer.
The differential input receiver is used to accept the
USB data signal according to the full-speed (12 MB/s)
USB driver characteristics (USB SPEC 1.1 - 7.1.4).
The UAC 3552A is shipped with a preprogrammed
EEPROM that allows normal USB functionality even if
no reprogramming is performed on the customer’s
side.
2.1.1.2. Interface Engine
The interface engine comprises two major sections:
the transceiver logic and the receiver logic. The trans-
ceiver logic transmits data packets built in memory by
the microcontroller. These packets are converted from
a serial to a parallel data stream. This includes NRZI
encoding, bit stuffing, CRC-computation, and addition
of SYNC field and EOP. The receiver logic will receive
USB data and stores these packets in its memory for
processing by the microcontroller. Serial USB data is
converted to a byte-wide parallel data stream and
stored in system memory. In addition to USB basic
data decoding, the Rx logic performs a PID check and
protocol layer checks.
The EEPROM can be programmed via USB by means
of UAC 3552A application tools.
2.1.2. Audio Control Interface
The audio control interface links the microcontroller to
the DSP and is used to initialize the DSP and to trans-
mit audio-related USB control data, like volume setting,
tone control etc.
2.1.3. Audio Streaming Interface
2.1.1.3. Microcontroller
The audio streaming interface directly connects the
serial interface engine to the DSP in order to transmit
the digital audio data. The interface collects and buff-
ers the burst audio data for further processing by the
audio processing unit.
The microcontroller manages buffers for all enabled
endpoints and interacts with the interface engine. The
buffers are built and decoded in memory. This way, the
microcontroller realizes the USB protocol handling, like
USB reset, enumeration, and all chapter 9 processing,
error handling, as well as class-specific endpoint han-
dling, like audio class and HID class. The audio-class
processing consists of interpreting the USB audio
commands and accordingly controlling the DSP-audio
function through a dedicated audio-control-interface to
the DSP. HID class processing means polling keys pro-
viding the corresponding key-codes to the host-com-
puter’s requests. These keys are connected to the
GPIO-pins. The RAM can be accessed by the micro-
controller and by the interface-engine’s DMA-control-
ler. All endpoint communication is realized with intelli-
gent buffer management built up in the RAM.
2.1.4. Audio Processing Unit
The audio processing unit is a powerful DSP core
which allows high-quality sample conversion, base-
band audio processing, and interpolation filtering used
for oversampling DAC, as well as customized algo-
rithms. For more details on the software see Section
2.2.2. “Audio Processing Software” on page 11.
2.1.5. Analog Back-end
A part of the RAM is reserved for download software.
This allows adding extra functionality to the GPIO pins,
like I2C-handling or any other control of external com-
ponents via USB. Downloading is handled by an extra
driver which allows direct RAM/ROM access via USB.
The analog back-end comprises the audio DAC, ana-
log filters, input mixer, op amps for optimal external
postfiltering, analog volume and mute, and the output
amplifier.
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