DATA SHEET AND USER GUIDE

Transcription

1 V L S I I P O W N E D B Y A V I R A L M I T T A L Mp3HufDec DATA SHEET AND USER GUIDE

2 Mp3HufDec ISO LAYER III HUFFMAN DECODER. ISO Layer III or commoly called as Mp3, employs Huffma ecodi techique to compress data, alo with other compreso schemes. Our product Mp3HufDec is deed to decode the Huffma coded data preset i a Mp3 ecoded file. Its writte u VHDL, ad is fully sythezeable. Mai Features: Sythezeable le clock VHDL RTL core, with testbech. No memory Decoder : it dos NOT use ay memory to decode the icomi bit stream No latecy Decoder: O/p values are produced at the very ext clock ede, as the correspodi iput is received by the decoder. Low Gate Cout : Less tha 5K ates o TSMC 0.18u Tech Deed u HufGe : our tool for eeric Huffma Decoder De Low lice Cost: $4000 for Sile Use Source. What is the Huffma Decoder supposed to do? As per the specificatios, of ISO Layer III, the frequecy spectrum of the audio al is packed i the bit stream as 2 raules per frame for each chael(the umber of chaels ca be either 1 or 2), ad each raule is cost of 576 frequecy samples, or frequecy lies. Out of these 576 frequecy lies, bi_values pairs of lies are coded u oe of the 17 uique(32 i all) Huffma tables, cout1 quadruples are coded u oe of the 2 huffma tables for the quadruples, ad the rest(576 2 x bi_values 4 x cout1) are zeros, they are also called rzeros. The task of the Huffma decoder is to decode these frequecy lies, ad produce correspodi values with their s. The codi of the frequecy lies represeted by bi_values has a special field associated with them called the libits. libits umber of bits will may follow a bi_value if, the maitude of the correspodi bi_value is equal to 15. Value of libits are ive i the specs with each Huffma table. The bit stream sytax cotaii the Huffma codes is ive i the ISO specificatios, uder the fuctio Huffmacodebits(). The task of the Huffma decoder is to produce these 576-rzeros frequecy lies for each raule with their correct ad maitude. For each Huffma coded bi_value, there are 2 decoded frequecy lies called is_x_out ad is_y_out. For each Huffma coded cout1, there are 4 decoded frequecy lies called is_v_out_quad, is_w_out_quad, is_x_out_quad, is_y_out_quad. The presece of a valid is_x_out ad is_y_out is idicated by huf_output_valid. The presece of is_v_out_quad, is_y_out_quad, is_x_out_quad, is_y_out_quad is idicated by huf_output_valid_quad. 2

3 The Iterface to the Huffma decoder : Pi Name IN/OUT Descriptio. clk_i IN Clock iput for the de clr_ IN Asyc reset for the de whe 0, put the de i reset, whe 1, let the de work. mp3bit_stream IN Huffma coded bitstream as per Huffmacodedbits() start IN Idicates valid Huffma data correspodi to bi_values part of the spectra, is valid at mp3bit_stream. This al must be put to 1 to idicate that the curret bit stream o the iput correspods to the bi_values reio of the spectra. start_quad IN Idicates valid Huffma data correspodi to cout1 part of the spectra is valid at mp3bit_stream. This al must be put to 1, to idicate that the curret bit stream o the iput correspods to the cout1 reio of the spectra table_sel IN(4:0) A 5 bit iput al which idicates which of the 32 tables is to be used for decodi bi_values. cout1_tablesel IN Sial bit iput al, to idicate which oe of the 2 quadruple tables is to be used for decodi cout1 values foud OUT It oes to 1, ad idicates that the Huffma decoder has just foud a code word i the iput bit stream(mp3bit_stream al). This code word belos to the bi_values reio of the spectra foud_quad OUT It oes to 1, ad idicates that the Huffma decoder has just foud a code word i the iput bit stream(mp3bit_stream al). This code word belos to the cout1 reio of the spectra is_x_out is_y_out OUT(13:0) The decoded x value correspodi to a bi_value Huffma code OUT(13:0) The decoded y value correspodi to a bi_value Huffma code 3

4 _x OUT Si bit for is_x_out _y OUT Si bit for is_y_out is_v_out_quad OUT(3:0) The decoded v value correspodi to a cout1 Huffma code. is_w_out_quad OUT(3:0) The decoded w value correspodi to a cout1 Huffma code. is_x_out_quad OUT(3:0) The decoded x value correspodi to a cout1 Huffma code. is_y_out_quad OUT(3:0) The decoded y value correspodi to a cout1 Huffma code. _v_quad OUT Si bit for is_v_out_quad _w_quad OUT Si bit for is_w_out_quad _x_quad OUT Si bit for is_x_out_quad _y_quad OUT Si bit for is_y_out_quad huf_output_valid OUT Idicates the presece of two valid decoded values is_x_out ad is_y_out beloi to the bi_value reio of spectra. Whe 1, the is_x_out ad is_y_out cotais valid decoded values huf_output_valid_quad OUT Idicates the presece of 4 valid decoded value belos is_v_out_quad, is_w_out_quad, is_x_out_quad ad is_y_out_quad beloi to the bi_value reio of spectra. Whe 1, the is_v_out_quad, is_w_out_quad is_x_out_quad ad is_y_out_quad cotais valid decoded values 4

5 Mp3HufDec clk_i clr_ mp3bit_stream start start_quad table_sel[3:0] cout1_tablesel foud foud_quad is_x_out[13:0] _x is_y_out[13:0] _y is_v_out_quad[3:0] _v_quad is_w_out_quad[3:0] _w_quad is_x_out_quad[3:0] _x_quad is_y_out_quad[3:0] _y_quad huf_output_valid huf_output_valid_quad Fiure 1: The Etity for Huffma Decoder with its I/Os. 5

6 Sectio 2. Worki of the Huffma Decoder. It is stroly recommeded that the reader should o throuh the sytax of huffmacodedbits(), i appedix A, before readi this sectio. As soo as oe of the iputs start or start_quad oes to 1, ad clr_, is ot eabled i.e its set to 1, ad there is a rui clock at the clk_i iput, Huffma decoder starts worki. As soo as the iput bitstream matches, a Huffma code from the table ive by table_sel (i case start is 1 ad start_quad is 0), foud oes 1 i the same clock cycle. As per the sytax of huffmacodedbits(), depedi upo the correspodi decoded values, i.e x,y from the table, the ad the libits correspodi to each decoded value(x ad y) follows hcod(x,y) i a maer described i huffmacodedbits(). The elemets that may follow a hcod are libits(x), if x = 15 ad libits!=0, for the table correspodi to table_sel Si(x), if x!= 0 libits(y), if y = 15 ad libits!=0, for the table correspodi to table_sel (y), if y!= 0 After all the expected elemets correspodi to a hcod, are received by the Huffma decoder, it produces fial values _x_out ad _y_out alo with their _x ad _y, ad the output al huf_output_valid is put to 1. The user ca use huf_output_valid al to clock i the data from the Huffma decoder. Fiure 2 below ives a example of Huffma decodi u Mp3HufDec, with 2 codes bei decoded from table umber 24(libits = 4). The first code word(hcod x, y ) bei decoded is which correspods to x=3,y=15. Sice x is ot equal to 15, o libits for x are expected. Sice x is ot equal to 0, therefore a bit for x is expected immediately after hcod( x, y ). Sice y is equal to 15, therefore libits for y (libitsy, 4 bits) are expected immediately after (x). Sice y ot equal to 0, bit for y is expected immediately after libitsy (show to be equal to 0011 i Fiure 2). The fial value of x is therefore -3, ad fial value for y therefore +18, (which comes from y + libitsy ).(Remember bit = 1 => -ive umber, ad bit = 0 => +ive umber) Similarly it ca be see that the secod hcod( x, y ), which is show to be 1100 is followed by just (x), (y), ivi x = +1, ad y = +1. The decodi of the frequecy spectrum represeted by cout1 is also decoded i milar fashio as the bi_values reio, but i cout1 reio, there are o libits ad istead of juxt x or y, there are four decoded values istead of 2 i.e v, w, x, y. The fial values are called is_v_out_quad, is_w_out_quad, is_x_out_quad, is_y_out_quad with their bits as _v_quad, _w_quad, _x_quad, _y_quad. These values are qualified by a presece of huf_output_valid_quad. Note that oly oe of the outputs, either huf_output_valid or 6

7 clr_ start mp3bit_stream hcod( x, y ) x=3,y=15 foud huf_output_valid _x_out _y_out table_sel = 24 x libitsy y hcod( x, y ) x=1,y= Fiure 2. A example, where the huffma decoder is decodi a bit stream, havi codes from Table Number 24(libits = 4) x y -1-1 huf_output_valid_quad ca be active at ay ive time, provided, the iputs start ad start_quad are ot applied multaeously. The outputs foud ad foud_quad are very helpful for user, as these ca be used by user to keep a accout of a couter which couts how may decoded values have bee received by user. For example if there exists a couter called huf_codes_couter the this couter should be icremeted by 2, wheever foud oes to 1, ad it should also be icremeted by 4, wheever foud_quad oes hih for each clock cycle. If either foud or foud_quad is 1 cotiuously for clock cycles, where >1, the it defiitely meas that the huf_codes_couter should be icremeted by Case I: 2 for each umber of clock cycles, foud was 1, i.e after the ed of clock cycles, the huf_codes_couter should have bee icremeted by *2. Case II: 4 for each umber of clock cycles foud_quad was 1, i.e after the ed of clock cycles, huf_codes_couter should have bee icremeted by *4. For example if table_sel is 16, start is 1, ad mp3bit_stream is 1 for clock cycles. It meas that the iput bit stream is cost of code words, correspodi to first etry i the table where hcod( x, y ) = 1. User should update the value of table_sel if reio boudary has bee discovered, i.e huf_code_couter = (umber of codes i a reio -2) ad foud has bee received. For 7

8 example, i the bi_values reio of the spectrum if umber of codes i reio0 are 48, the if huf_code_couter reaches 46, ad a foud has bee asserted, user should switch the value of table_sel to poit the correct table_sel for reio1. The ew table_sel will ot come ito affect, util all the bits ad libits of 24 th hcod has bee received by the Huffma decoder. This example is also illustrated i Fiure 3 below. Note that eve after table_sel has bee updated i clock period umber 9, soo after foud has bee detected, the fial values i.e _x_out ad _y_out produced as output i clock period umber 15, belos to table Number 24(idetified by previous table_sel value). Hece from this poit of time the _x_out ad _y_out will belo to table Number 15(idetified by ew table_sel value. The values _x_out = 0, ad _y_out = -1 produced i clock period umber 21, thus belos to table umber 15. clr_ start mp3bit_stream hcod( x, y ) x=3,y=15 foud huf_output_valid _x_out _y_out table_sel = 24 x libitsy y hcod( x, y ) x=0,y=1 huf_code_couter = 46 huf_code_couter = table_sel = 15 Fiure 3. A example, to show whe the table_ must be updated, if the umber of codes reaches a reio boudary y ew hcode Sectio 3. Testi of the Huffma decoder. Testi of the Huffma decoder is doe u various test cases. Test Case I. This test case exercises each hcod preset i each of the 17 uique Huffma tables for bi_values reio, ad each hcod preset i both the quad tables, ive i the specificatios. This test case is called EXHAUST1. Correspodi testbech is huffma_tb_exhaust1.vhdl 8

9 Test Case II. This test case exercises hcod form some real.mp3 files. 9