Add support for 6551 IRQ mode

6551_irq.asm

@@ -0,0 +1,131 @@
+; 6502 BIOS 
+; Based on original code by Daryl Rictor
+; Adapted to 6551 ACIA board for RC2014
+; This implementation uses IRQ
+; NOTE: The 6551 ACIA works with the 6502 card for simple Monitor functions
+; However, loading an Intel HEX file appears to overwhelm the ACIA.
+;
+;
+; ----------------- assembly instructions ---------------------------- 
+;
+; this is a subroutine library only
+; it must be included in an executable source file
+;
+;
+;*** I/O Locations *******************************
+; Define the i/o address of the UART chip
+;*** 6551 ACIA ************************
+
+uart_base               = $c0a0
+uart_data_reg           = $c0a0
+uart_status_reg         = $c0a1
+uart_command_reg        = $c0a2
+uart_control_reg        = $c0a3
+uart_xmit               = uart_data_reg     ; Used by upload.asm
+
+;
+;***********************************************************************
+; UART I/O Support Routines
+; We'll use Daryl's routine names for compatibility with his software/code
+; Otherwise, we'll use UART-agnostic nomemclature
+
+;---------------------------------------------------------------------
+
+ACIA1_init
+uart_init
+                lda     #>uart_irq
+                ldx     #<uart_irq
+                stx     irq_vector
+                sta     irq_vector+1
+                jsr     init_buffer     ; Initialize IRQ buffer
+                
+                ; Software reset
+                lda     #$00
+                sta     uart_status_reg
+                
+                ; 0000 1001     -> recv irq
+                lda     #$09
+                sta     uart_command_reg
+                
+		; 0001 1110
+                lda     #$1e    ; 9600 baud, /16, 8+1
+                sta     uart_control_reg
+                
+                rts                     ; done
+                
+;---------------------------------------------------------------------
+; Input char from UART (blocking)
+; Exit: character in A
+ACIA1_Input
+uart_input
+                jsr     check_buffer
+                beq     uart_input
+                jsr     pull_buffer
+                rts                      ;
+
+;---------------------------------------------------------------------
+; Non-waiting get character routine 
+; Scan for input (no wait), C=1 char, C=0 no character
+ACIA1_Scan
+uart_scan
+                clc
+                jsr     check_buffer
+                beq     uart_scan2
+                jsr     pull_buffer     ; Exit with C=1
+uart_scan2
+                rts
+
+;---------------------------------------------------------------------
+; output to OutPut Port
+; Entry: character in A
+; Exit: character in A
+ACIA1_Output
+uart_output   
+                pha                      ; save registers
+uart_out1     
+                lda   uart_status_reg           ; serial port status
+                and   #$10              ; is tx buffer empty
+                beq   uart_out1         ; no
+                pla                     ; get char
+                sta   uart_data_reg     ; Write character to Port
+                rts                     ; done
+                
+;------------------------------------------------------------------------------
+; This is the UART-specific call to bring RTS high to disable transmit from terminal
+; We can use A
+uart_deassert_rts
+;                lda     uart_command_reg
+;                and     #$f3            ; bits 3-2 = 0
+;                sta     uart_command_reg
+                rts
+
+;------------------------------------------------------------------------------
+; This is the UART-specific call to bring RTS low to re-enable transmit
+
+uart_assert_rts
+;                lda     uart_command_reg
+;                ora     #$08            ; bit 3 = 1
+;                sta     uart_command_reg
+                rts
+
+;---------------------------------------------------------------------
+uart_irq
+                ; Check if our interrupt
+                lda     uart_status_reg      ; Serial port status
+                tax             
+                and     #$88           ; is irq
+                beq     ui_end         ; no char to get
+                and     #$08
+                bne     ui_isours
+                brk                     ; Breakpoint if not our interrupt
+ui_isours
+                ; It's our interrupt
+                lda     uart_data_reg           ; get chr
+                jsr     put_buffer
+                
+ui_end
+                jmp     null_irq
+                
+        .include        buffer.asm
+;
+;end of file

sbc.asm

@@ -20,11 +20,12 @@
 
         ; Change this line according to the type of UART board 
 ;        .include rruart.asm     ; uart init
-;      	 .include 16c550.asm
+      	 .include 16c550.asm
 ;        .include 16c750.asm
 ;        .include 6850.asm
 ;        .include 16c550_irq.asm
-        .include 6551.asm
+;        .include 6551.asm
+;        .include 6551_irq.asm
 
  	.include sbcmon.asm         ; actual monitor