Rapid Prototyping using a Microprocessor Core on a Spartan II FPGA

Rapid Prototyping using a Microprocessor Core on a Spartan II FPGA A Digilent Prototyping Board Xilinx Spartan IIE FPGA The FC16 Forth Core Rapid Prototyping of the DIO2 Peripheral Board DIO2 buttons, LEDs, and 7-seg displays Multiplication and Division The Liquid Crystal Display A Simple Decimal Calculator Summary

Digilab 2E – Spartan IIE www.digilentinc.com

Digilab 2E – Spartan IIE

Digilab IO2 Board 16x2 character LCD Four seven segment displays 16 LEDs in three colors 8 switches 15 pushbutton keypad 8-bit VGA port PS/2 port

Digilab IO2 Board

Accessing the DIO2 Peripheral Board cs oe we addr(5:0) data(7:0) 1 xxxx00 btns(7:0) xxxx01 ‘0’&btns(14:8) xxxx1x switchs 000100 leds(7:0) 000101 leds(15:8) 000110 sseg_reg(7:0) 000111 sseg_reg(15:8)

The FC16 Forth Core

The Data Stack

Data Stack Instructions Hex Opcode Name Function 0000 NOP No operation 0001 DUP Duplicate T and push data stack. N <= T; N2 <= N; 0002 SWAP Exchange T and N. T <= N; N <= T; 0003 DROP Drop T and pop data stack. T <= N; N <= N2; 0004 OVER Duplicate N into T and push data stack. T <= N; N <= T; N2 <= N; 0005 ROT Rotate top 3 elements on stack clockwise. T <= N2; N <= T; N2 <= N; 0006 -ROT Rotate top 3 elements on stack counter-clockwise. T <= N; N <= N2; N2 <= T; 0007 NIP Drop N and pop rest of data stack. T is unchanged. N <= N2; 0008 TUCK Duplicate T into N2 and push rest of data stack. N2 <= T; 0009 ROT_DROP Drop N2 and pop rest of data stack. T and N are unchanged. Equivalent to ROT DROP 000A ROT_DROP_SWAP Drop N2 and pop rest of data stack. T and N are exchanged. Equivalent to ROT DROP SWAP

The FC16 Forth Core

Funit16 Instructions (fcode = lower 6 bits of opcode) Hex Opcode Name Function 0010 + Pop N and add it to T. 0011 - Pop T and subtract it from N. 0012 1+ Add 1 to T 0013 1- Subtract 1 from T 0014 INVERT Complement all bits of T. 0015 AND Pop N1 and AND it to T. 0016 OR 0017 XOR 0018 2* Logic shift left T. 0019 U2/ Logic shift right T. 001A 2/ Arithmetic shift right T. 001B RSHIFT Pop T and shift N1 T bits to the right. 001C LSHIFT Pop T and shift N1 T bits to the left. 001D mpp multiply partial product (used for multiplication) 001E shldc shift left and decrement conditionally (used for division)

Funit16 Instructions (cont.) (fcode = lower 6-bits of opcode) Name Function 0020 TRUE Set all bits in T to ‘1’. 0021 FALSE Clear all bits in T to ‘0’. 0022 NOT 0= TRUE if all bits in T are ‘0’.   0023 0< TRUE if sign bit of T is ‘1’. 0024 U> T <= TRUE if N > T (unsigned), else T <= FALSE 0025 U< T <= TRUE if N < T (unsigned), else T <= FALSE 0026 = T <= TRUE if N = T, else T <= FALSE 0027 U>= T <= TRUE if N >= T (unsigned), else T <= FALSE 0028 U<= T <= TRUE if N1 <= T (unsigned), else T <= FALSE 0029 <> T <= TRUE if N /= T, else T <= FALSE 002A > T <= TRUE if N1 > T (signed), else T <= FALSE 002B < T <= TRUE if N1 < T (signed), else T <= FALSE 002C >= T <= TRUE if N1 >= T (signed), else T <= FALSE 002D <= T <= TRUE if N1 <= T (signed), else T <= FALSE

The FC16 Forth Core

Return Stack

Return Stack Instructions Name Function >R “To-R” Pop T and push it on return stack R> “R-from” Pop return stack R and push it into T R@ “R-fetch” Copy R to T and push register stack R>DROP “R-from-drop” Pop return stack R and throw it away DRJNE Decrement R and jump if R is not zero CALL (:) Call subroutine (colon) RET (;) Subroutine return (semi-colon)

The FC16 Forth Core

Top Level Design

DIO2 and Transfer Instructions Name Function #ClkCyc DIO2@ Fetch the 8-bit byte from the DIO2 data bus and load it into T. 1 DIO2! Store the byte in N at the DIO2 address in T. Pop both T and N 3 LCDinst! Write instruction in N to the DIO2 LCD. 8 LCDdata! Write data in N to the DIO2 LCD. JMP Jump to inline address 2 JZ Jump if all bits in T are ‘0’ and pop T

\ Test of DIO2 buttons, LEDs, and 7-seg disp : D2DIG! ( n -- ) DUP 8 RSHIFT \ n nHI 7 DIO2! \ display nHI 6 DIO2! ; \ display nLO : D2LD! ( n -- ) DUP 8 RSHIFT \ n nHI 5 DIO2! \ display nHI 4 DIO2! ; \ display nLO : get.BTN2( -- n ) 1 DIO2@ \ btns(15:8) 8 LSHIFT 0 DIO2@ \ btns(7:0) OR ; cs oe we addr(5:0) data(7:0) 1 xxxx00 btns(7:0) xxxx01 ‘0’&btns(14:8) xxxx1x switchs 000100 leds(7:0) 000101 leds(15:8) 000110 sseg_reg(7:0) 000111 sseg_reg(15:8)

1 : waitBTN2 ( -- n) BEGIN \ wait to lift finger get.BTN2 0= UNTIL 1 : waitBTN2 ( -- n) BEGIN \ wait to lift finger get.BTN2 0= UNTIL BEGIN \ wait to press button get.BTN2 get.BTN2 ; \ get buttons : but>num ( n1 – n2 ) 15 FOR \ loop 15 times DUP 1 = IF \ value matches R> \ get loop value 15 SWAP - \ find index 1 >R \ break out of loop ELSE U2/ \ Shift button value THEN NEXT NIP ; \ remove extra 1 from N

\ Test of DIO2 buttons, LEDs, and 7-seg disp : main( -- ) BEGIN waitBTN2 \ wait to push BTN2 DUP D2LD! \ display on LEDs but>num \ find button number D2DIG! \ display on 7-seg disp AGAIN ;

Multiplication UM* ( u1 u2 -- upL upH ) T N N2 mpp mpp mpp mpp ROT_DROP ; mpp (multiply partial product) if N(0) = 1 then adsh else sh end if; : * ( n1 n2 – n1*n2 ) UM* DROP ;

Division shldc Dividend T N N2 Divisor sll T & N; if T[16:8] > N2 then T := T - (0 & N2); N(0) := ‘1’; end if; Dividend T N N2 Divisor

32 / 16 = 16:16 Unsigned Division : UM/MOD ( unL unH un -- ur uq ) -ROT shldc shldc shldc shldc ROT_DROP_SWAP ;

32 / 16 = 32:16 Unsigned Division : MU/MOD ( ud un -- urem udquot ) >R 0 R@ \ udL udH 0 un UM/MOD \ udL remH quotH R> \ udL remH quotH un SWAP >R \ udL remH un UM/MOD \ remL quotL R> ; \ remL quotL quotH

LCD Display

DIO2 and Transfer Instructions Name Function #ClkCyc DIO2@ Fetch the 8-bit byte from the DIO2 data bus and load it into T. 1 DIO2! Store the byte in N at the DIO2 address in T. Pop both T and N 3 LCDinst! Write instruction in N to the DIO2 LCD. 8 LCDdata! Write data in N to the DIO2 LCD. JMP Jump to inline address 2 JZ Jump if all bits in T are ‘0’ and pop T

LCD.WHP HEX : 1ms_Delay( -- ) 30D1 FOR NEXT ; : 30ms.Delay ( -- ) 1E FOR 1ms_Delay NEXT ; : lcd.init ( -- ) 30ms.delay 3C 0 LCDinst! \ 2 x 40 display 1ms_Delay 0f 0 LCDinst! \ display on 1 0 LCDinst! \ display clear 1ms_Delay 1ms_Delay 6 0 LCDinst! \ entry mode 1ms_Delay ;

LCD.WHP (cont.) : clear.lcd( -- ) 1 0 LCDinst! \ display clear 1ms_Delay 1ms_Delay ; : crlf.lcd( -- ) C0 0 LCDinst! \ set address 40 : hex2asc ( n -- asc ) F AND \ mask upper nibble DUP 9 > \ if n > 9 IF 37 + \ add $37 ELSE 30 + \ else add $30 THEN ;

LCD.WHP (cont.) : hex>lcd ( hex -- ) hex2asc 0 LCDdata! 1ms_Delay ; : u.lcd ( u -- ) DUP C RSHIFT hex>lcd DUP 8 RSHIFT DUP 4 RSHIFT hex>lcd ;

A simple decimal calculator HEX : get.dec ( -- n k ) \ k = non-dec key 0 \ decimal # n in hex BEGIN waitBTN2 but>num \ press button DUP A < \ while 0 - 9 WHILE DUP hex>lcd \ display on lcd SWAP A * + \ convert to hex REPEAT ; : display.dec( ud -- ) 1 >R \ save count A MU/MOD OVER OVER XOR WHILE \ while dquot <> 0 R> 1+ >R \ inc count REPEAT DROP DROP \ drop 0 0 R> \ get count FOR hex>lcd \ display all digits NEXT ;

A simple decimal calculator (cont.) : main( -- ) lcd.init BEGIN get.dec \ enter decimal number DUP E = \ followed be E key WHILE clear.lcd DROP REPEAT DUP C = \ press C key to IF DROP UM* \ multiply clear.lcd display.dec \ display product ELSE DUP D =\ press D key to 0 SWAP UM/MOD \ divide clear.lcd 0 display.dec \ display quotient crlf.lcd 0 display.dec \ display remainder B = \ press B key to DROP clear.lcd \ clear the display THEN AGAIN ; A simple decimal calculator (cont.)

Digilab IO2 Board 16x2 character LCD Four seven segment displays 16 LEDs in three colors 8 switches 15 pushbutton keypad 8-bit VGA port PS/2 port

Summary A Forth core has been implemented on a Xilinx Spartan II FPGA This Forth core allows rapid prototyping of the Digilent DIO2 board Easy access to the LEDs, 7-segment displays, LCD display, switches, and pushbuttons Demonstrated by implementing a simple decimal calculator