.CR 8080 .EB OFF .TF BOOTLOAD.HEX,INT .LI off ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ; ; ; 8080 CPU Bootloader ; ; ; ; This is a simple bootloader that will write data to memory that is sent ; ; over the UART. It occupies a little over half of a 768 byte ROM. ; ; ; ; It has three commands: ; ; * Waaaadd - 'Write' - where aaaa is the address and dd is the data. Note ; ; that all numerals are in CAPITAL hexadecimal, as are all the ; ; commands. This command will echo back the address and the ; ; data that was written, however, if the address is in the ROM's ; ; address space this will be data FROM THE ROM, so it will not ; ; match what was written to the RAM. Note that the Python ; ; programmer does not check the data written below 0x2FF (the ; ; high address of the ROM) for this very reason. ; ; * C - 'Clear' - clears the RAM. ; ; * D - 'Done' - this will write a one to the switch register and ; ; activate the RAM, thus resetting the CPU and ; ; executing whatever is in RAM. ; ; ; ; The bootloader uses the top end of the RAM as a small stack space. It would ; ; be possible to get rid of the need for a stack altogether by 'unrolling' the ; ; code but I was too lazy, so I just made sure that the programs I was loading ; ; didn't have anything near the end of the RAM. ; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ; ; ; Copyright (c) 2008 Mike Roddewig. ; ; All rights reserved. ; ; ; ; Redistribution and use in source and binary forms, with or without ; ; modification, are permitted provided that the following conditions are met: ; ; * Redistributions of source code must retain the above copyright notice, ; ; this list of conditions and the following disclaimer. ; ; * Redistributions in binary form must reproduce the above copyright ; ; notice, this list of conditions and the following disclaimer in the ; ; documentation and/or other materials provided with the distribution. ; ; ; ; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ; ; "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED ; ; TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR ; ; PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR ; ; CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, ; ; EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, ; ; PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; ; ; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, ; ; WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR ; ; OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ; ; ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. ; ; ; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; .OR $0000 ; ; UART equates ; TTS: .EQ $20 TTI: .EQ $21 TTO: .EQ $21 TTYDA: .EQ $01 TTYTR: .EQ $80 SWITCH: .EQ $00 ; Address of the memory switch peripheral. MEM_HIGH: .EQ $FFFF ; The highest memory address. START: MVI A,$00 MVI B,$00 MVI C,$00 MVI D,$00 MVI E,$00 MVI H,$00 MVI L,$00 LXI SP,MEM_HIGH-20 ; Setting up the stack space. LXI H,WMES CALL PRINT JMP CLEAR ; Clear the memory at start-up PROGRAM: CALL IN8 MOV B,A MVI A,'D' CMP B JZ DONE MVI A,'W' CMP B JZ WRITE MVI A,'C' CMP B JZ CLEAR JMP PROGRAM ; This routine will clear the ram (including the stack!!!) CLEAR: CALL OUT8 LXI H,$0000 MVI A,$FF CLEAR_LOOP: MVI M,$00 CMP H JZ CLEAR_LB CLEAR_INC: INX H JMP CLEAR_LOOP CLEAR_LB: CMP L JNZ CLEAR_INC CALL CRLF JMP PROGRAM ; This subroutine will terminate the bootloader. DONE: CALL OUT8 CALL CRLF MVI A,$01 OUT SWITCH ; This will reset the processor... NOP_LOOP: NOP JMP NOP_LOOP WRITE: CALL OUT8 CALL GET_ADDR CALL IN8 CALL ATOH RLC RLC RLC RLC MOV B,A CALL IN8 CALL ATOH ADD B MOV M,A ; Store data to memory. CALL W_ADDR ; Echo the address back MOV A,M ; Load the data back. CALL WRITE_A CALL CRLF JMP PROGRAM ; This subroutine will write the byte in A to the UART. WRITE_A: MOV C,A ; Save the byte ANI $F0 RRC RRC RRC RRC CALL HTOA MOV B,A CALL OUT8 MOV A,C CALL HTOA MOV B,A CALL OUT8 RET ; This subroutine will convert an ASCII hex number in A ; to a number. ATOH: CPI '9'+1 JC ATOH_NUM ATOH_CHAR: SUI $37 JMP ATOH_DONE ATOH_NUM: SUI $30 ATOH_DONE: ANI $0F RET ; This subroutine will convert a number in A ; to a character. HTOA: ANI $0F CPI 10 JC HTOA_NUM ADI $37 JMP HTOA_DONE HTOA_NUM: ADI $30 HTOA_DONE: RET ; This subroutine will write the address in HL to the ; UART. W_ADDR: MVI D,1 W_ADDR_L: MOV A,D CPI 0 JZ W_ADDR_D MOV A,H CALL WRITE_A DCR D JMP W_ADDR_L W_ADDR_D: MOV A,L CALL WRITE_A RET ; This subroutine reads an address from the UART into HL. GET_ADDR: MVI C,1 GET_LOOP: CALL IN8 CALL ATOH RLC RLC RLC RLC MOV B,A CALL IN8 CALL ATOH ADD B MOV B,A MOV A,C CPI 0 JZ GET_DONE MOV H,B DCR C JMP GET_LOOP GET_DONE: MOV L,B RET ; This subroutine will print a null-terminated string ; with the starting address loaded into HL. PRINT: MOV B,M ; fetch character MVI A,$00 ; null CMP B ; character = null? RZ CALL OUT8 INX H JMP PRINT ; This subroutine sends the character in B to the ; UART. OUT8: IN TTS CMA ANI TTYTR JZ OUT8 MOV A,B OUT TTO RET ; This subroutine fetches a character from the UART ; and returns it in A. IN8: IN TTS CMA ANI TTYDA JZ IN8 IN TTI RET CRLF: MVI B,13 ; cr CALL OUT8 LF: MVI B,10 ; lf CALL OUT8 RET WMES: .DB '8080 Bootloader',13,10 .DB 'Mike Roddewig 2008',00