The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL

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1 Yu will learn the fllwing in this lab: The UNIVERSITY f NORTH CAROLINA at CHAPEL HILL Cmp 541 Digital Lgic and Cmputer Design Spring 2016 Lab Prject (PART A): A Full Cmputer! Issued Fri 4/8/16; Suggested cmpletin date 4/18/16 Designing a mdule with multiple memries Designing and using a bitmap fnt Designing a memry-mapped display Understanding initializatin f a memry unit using an external file Part 0: Thrughly test yur design f the MIPS CPU frm Lab 10 Befre yu prceed with the tasks belw, make sure that yur MIPS CPU frm Lab 10 is wrking crrectly. The tester prvided fr Lab 10 shuld result in all crrect utputs (i.e., all ERROR signals shuld be green). Part 1: Design a full display unit ( Terminal Display ) Yu will build upn yur VGA display driver frm Lab 7 t make it a full-fledged character display. The blck diagram belw shws yur design frm Lab 7: This earlier design simply generated a fixed pattern t shw n the display (e.g., lines, checkerbard pattern, etc.). In this assignment, yu will extend it t display a 2-D grid f characters, i.e., a character display, as shwn in the blck diagram belw. 1

2 The characters t display are assigned cdes (yur chice), and these cdes are stred in an array in a special memry called screen memry. The array is stred in rw-wise (rw 0 first, then rw 1, etc.), and left-t-right within each rw. If yur screen size is 640x480 pixels, and if yu decide n each character being 16x16 pixels, then each rw will have 40 characters, and there will be 30 rws. S, yur screen memry will need t have at least 1200 lcatins. There is als anther memry, a read-nly ne, called bitmap memry, which stres the pixel pattern fr each f the characters yu implement. S, fr example, if yur characters are blcks f 16x16 pixels, and if each pixel has an 8-bit RGB clr, then the bitmap memry will have 256 bytes stred fr each character yu chse t implement. If yur final applicatin needs 16 different characters, then yur bitmap memry will have 256 x 16 = 4096 bytes f data. Nte: There is n CPU in this picture yet. Study the blck diagram carefully. Make a tp-level mdule called tp, which cntains vgadisplaydriver (in a file named vgadisplaydriver.sv) and screenmem (in file screenmem.sv). The VGA display driver in turn cntains tw submdules: VGA Timer and Bitmap Memry. Nte the fllwing: VGA timer: Yu designed this mdule in Lab 7. Use a reslutin that yu wuld like fr yur final dem. In class/lab discussins, I will assume a reslutin f 640x480. If yu deviate frm this reslutin, be sure t make crrespnding changes t yur Verilg descriptin thrughut. 2

3 Screen memry: This memry cntains a linear sequence f values, each representing the cde fr a character. These are cdes yu assign t sme special characters (e.g., different clred blcks, r different types f smilie faces, etc.). It is sufficient t keep each cde 8-bits wide, althugh yu can use fewer bits if yu need fewer. Fr instance, if yu nly want t display 32 unique symbls, yu nly need a cde with 5 bits (yur cdes wuld run frm 5 b00000 t 5 b11111). The width f the screen address will depend n yur screen reslutin and character size. If, as in the text abve, yur screen has a ttal f 1200 characters, yu will need a screen address f 11 bits. Nte: Each lcatin in this memry shuld represent a single character s cde. Bitmap memry: This memry is indexed by the character cde, and stres the bitmap r fnt infrmatin fr that character. In particular, each character is a 2-dimensinal matrix f RGB values, stred in a linear sequence. S, fr example, if each character is a 16x16 square bx f pixels, yu will stre the 12-bit RGB value fr the (0,0) pixel fr that character first, then (0,1), and s n until the end f the tp rw, then the secnd rw, etc. Thus, there will be 256 clr values (each 12-bit in length) stred fr each character. Nte: Each lcatin in this memry shuld represent a single pixel s clr value. Keep the fllwing pints in mind as yu d this assignment: Start with nly a small number f characters (say, 2 r 4). If yur design wrks fine, increase the number f characters t a reasnable number (at least 8, but as many as yu think yu might need t d an interesting dem!). Yu may have t think a bit int yur final dem here, but dn t wrry, nce yu have the basic design wrking, it wn t be t hard t cme back and add mre characters and bitmaps t it! Initialize the screen memry frm a file using the $readmemh instructin. Yu shuld have the entire screen initialized in this file; therwise there may be junk character cdes in the part f the screen left uninitialized. This file will be lng (e.g., 1200 lines if yur screen has 40 clumns x 30 rws). Initialize the bitmap memry frm a file using the $readmemh (r perhaps $readmemb may be mre cnvenient here). If, fr example, characters are 16x16 pixels, then each will require 256 clr values t be stred in this memry. Start with nly a cuple f characters, then increase the number. This file can get lng! Fr example, it culd have 256 x 16 lines if yu are using 16 characters. The main challenge in this lab assignment is t instantiate the tw memry units, and t wire everything up tgether. This is a gd exercise in hierarchical design. That is the reasn I will nt be prviding a Verilg cde skeletn. The key challenge t designing this system is t figure ut the fllwing mappings: The mapping frm the (x,y) pixel crdinates generated by the VGA Timing Generatr, t the (J, K) character crdinates that that pixel maps t in Screen Memry. The mapping frm (J, K) character crdinates t the address in Screen Memry. The mapping frm the character cde that the Screen Memry gives yu, t the start lcatin f the bitmap stred fr that character in the Bitmap Memry. The mapping frm the (x,y) pixel crdinates generated by the VGA Timing Generatr, t the ffset within the bitmap fr that character in the Bitmap Memry. Start small s things are easier t debug. 3

4 Part 2: Integrate the CPU and the display unit using memry mapping As discussed in Lecture 16 (slides 3 and 5 [reprduced belw]), yu will integrate the CPU and the display using memry-mapped I/O. One pssible memry mapping scheme was discussed in class: Assigning the data memry t start at address 0x2000 allws yu t use the MARS assembler with the Cmpact, Text at 0 cnfiguratin, which places cde at 0x000 and data at 0x2000. T implement this memry map, use the blck diagram belw. Put the Memry and I/O unit in a mdule called memio, and name the file memio.sv. Fr nw, skip the jystick/keybard etc. We will discuss thse next week. 4

5 NOTE: The screen memry shwn in Part 1 has nw been placed inside the Memry and I/O unit. Therefre, the display driver nw utputs the address fr the screen memry, which ges int the memry-i/o unit thrugh a prt (shwn n the right side in the figure abve). This prt is distinct frm the prt used by the MIPS prcessr, and frm the prt that will be used by the keybard/jystick. Thus, the screen memry nw has separate interfaces t the display driver and t the MIPS CPU. Implement this part n the bards! Write a shrt prgram t have yur MIPS write characters t Screen Memry and see if they shw up n the mnitr! A sample prgram is prvided n the website; it waits fr an amunt f time that can be set in the assembly prgram, then write tw characters n the screen. If all ges well, yu will have a near-final full-functin cmputer. Gd luck! Start wrking n yur final prject dem. As explained in class, submit a shrt prpsal n what yu wuld like t implement fr yur final prject dem via Sakai by Mnday, Apr 11, 10 am. What t submit: [Part 1] The Verilg surce f yur tp-level display unit (vgadisplaydriver.sv). This file shuld cntain the Verilg descriptin f the three cmbinatinal lgic blcks fr generating RGB values fr each pixel. [Part 2] In a cuple f sentences, describe the set f characters yu have chsen t implement. [Part 3] The Verilg surce fr the memio mdule (memio.sv). In a cuple f sentences, state if everything wrks as yu expect, r if there are sme prblems yu still need t reslve. Shw a wrking dem f yur design fr Part 3 whenever ready. Hw t submit: Please submit yur wrk by whenever ready (if it is after 4/18, I d wrry): Send t: cmp541submit-cs@cs.unc.edu Use subject line: Lab Prject PART A Include the Verilg files as attachments as specified abve, and the rest in plain text. 5