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mindTunes . FPGA mp3/wav memo recording. Jonathan Chen, Po-Han Huang, Michael Kempf, Yen-Liang Tung, Christos Vezyrtzis. Object – Environment of System. Music/voice signals are band-limited signals. =. Memo storing dictates capacity instead of quality as primary concern . t. We need:
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mindTunes FPGA mp3/wav memo recording Jonathan Chen, Po-Han Huang, Michael Kempf, Yen-Liang Tung, Christos Vezyrtzis
Object – Environment of System Music/voice signals are band-limited signals = Memo storing dictates capacity instead of quality as primary concern t • We need: • Low complexity system • Widely accepted storage format and medium • Therefore: • Minimize sampling rate (8kHz) and bit analysis (16 bit) • Choose wav/mp3 and USB Flash Drive
Hardware Setup (i-side only) • Programmable A/D converter • 1-bit output stream : Use S/P • 8kHz sampling rate, dual channel • No pre-filtering • Same setting for D/A • Why only input? Symmetry • Output of hardware: at request of the processor / encoder • Very quick sample demand, very slow sampling • Solution: HARDWARE MUST SLOW DOWN THE SOFTWARE • How long? As much as it takes !!
S/P & Clock Setup (FYI) • Clocks are always created as fractions of the Audio Clock: 18.432MHz • 18.432MHz / 2304 = 8kHz (Sampling) • A/D Output must be converted to 16-bit word before the next sample • 18.432MHz / 144 = 128kHz (S/P) • Within 1-sample time interval we create one 16-bit word (sample)
FIFO • Processor much faster than A/D • Within 1 sample time : 6250 read commands but only 1 new sample !! • Pause processor until there is word to read from the FIFO • In the process of reading: • If there is a read command pause the processor • Put the word on the bus • Then read it!! • 3 cycle delay (w.r.t. processor clock)
FIFO(2) (FYI) • Questions: • How big? mp3 frame • Synchronous? NO Moore state machine • Input & Output FIFO equally spaced ? NO • Delay between successful reading and output word: 3 cycles
FIFO(3) • Operation: • Altera MegaFunction • One clock cycle after rdreq, data is presented at output q; usedw decrements • One clock cycle after wrreq, data is latched in; usedw increments • Underflow circuitry prevents data being read from an empty FIFO; FIFO blocks • Overflow circuitry prevents data being wrteen to a full FIFO; FIFO blocks
Timing Diagram (Input) (FYI) (3) FIFO is not empty prepares for output (1) Read & Write are de-assetred WAITREQUEST (4) FIFO is not empty & Read command data is on the bus (5) WAITREQUEST 0 and data is read (2) New sample arrives at the FIFO FIFO is ready for output
Operating System • uClinux – microcontroller implementation of Linux. • Enables the incorporation of device drivers – without having to write them!
Storage/File System • Utilized USB mass storage device • Running as a host device on DE2 • Once mounted, provides convenient storage of recordings in a “directory”
I/O programming in user space • Not kernel space - no interrupts • Can’t use Hardware Abstraction Layer (e.g. IORD16_Direct) • To access peripherals (switches, audio) use memory pointer access
WAV Format Recording • The ‘RIFF’ chunk descriptor • WAVE format • The ‘fmt’ sub-chunk • format of the sound information • The ‘DATA’ sub-chunk • size of the sound information and raw sound dat
MP3 Format (MPEG 1 Layer3) • MP3 is composed of succession of frames • i.e. frame1 - frame2 - frame3 -…….. • Each frame is totally independent, can cut any part of MPEG files and play correctly.
Choosing MP3 version • Since we want to user low sampling Rate - 8kz, we choose MPEG 2.5 • Layer3 • Note: The only difference MPEG 1,2,2.5 is MPEF 2 and 2.5 support more bit • rate, and sampling rate. Everything else are the same.
Encoding Implementation .Wav file At USB .mp3 file at USB ADC Encoding The reason to have .wav file in the transition is that the mp3 encoding algorithm is to slow to make it realtime
Encoding Implementation Take a code from shine fixed point version 1.09 which was originally used on ARM machine Strip out the part about ARM and change the part of assembly code to C in order to run under nios-uclinux Made it a function for main code to call
Decoding: Uclinux – MP3PLAY Support MPEG-1, 2, 2.5 Layer 1 2 3 Support both fixed-point and floating-point Can use Assembly to optimize the computing Implementation: Set to use fixed-point function in mp3dec library and do not use Assembly optimization Write out PCM data to FIFO input Add header on PCM data to write to WAV
Decoding Implementation .mp3 file at USB Decoding DAC .Wav file At USB
Problems – Comments • Software(Decoding): • Now, we can hear artist’s vocal in the background with lots of white noise • Before waitrequest function enable, it sounded like machine gun • With waitrequest enabled, artist’s voice sounds retarded • After we increased the FIFO size, the tempo is close to original clip • Write to wav file, but cannot hear sound • Write raw PCM data, listening on Matlab does not work • Software(Encoding): • Too slow to be real-time • Inline assembly optimization • Hardware mul() implementation
Problems – Comments • Hardware: • FIFO timing • Need to synchronize bus clock (100 MHz) and S. CLK (8 kHz) • Encoder/Decoder might be consuming/feeding data faster than ADC/DAC can process! • Need to increase size of FIFO • Asynchronous “wait” • waitrequest is combinational logic; state machine is sequential • Choice of Different configurations • Size of FIFO’s (mp3 frame) • Simulation : • Initial sample of FIFO undefined at output • Caused by Legacy mode (chosen as a suggestion of the software)
