fix kp values

Makefile

@@ -20,6 +20,7 @@ $(BUILD_DIR):
 	mkdir $@
 
 .PHONY: default test clean
+.DEFAULT_GOAL 	= default
 default: $(ROM)
 test: ../test.bin
 

details.md

@@ -1,13 +1,19 @@
 # Project details
 ## Address Space
-### RAM: $0-$7fff 
+|Name|From|To|r/w|
-### (EEP)ROM: $8000-$ffff
+|---|---:|---:|:---:|
+|ZEROPAGE   |$00    |$ff    |`rw`|
+|STACK      |$100   |$1ff   |`rw`|
+|RAM        |$200   |$4fff  |`rw`|
+|SPI        |$5000  |$5fff  |`rw`|
+|VIA1       |$6000  |$600f  |`rw`|
+|VIA2       |$7000  |$700f  |`rw`|
+|ROM        |$8000  |$ffff  |`r `|
 
 ## Naming conventions
 leading underscors `_` indicate a "private" label/variable, that is meant for internal use within the module only.
 ### Labels
-- `namespace_fname` for exported subroutines
+- **scopes**: snake case 
-- `_namespace_fname` or `_namespace_fname_sub` for internal labels
+- **subroutines** and **variables**: snake case (`scope::(_)fname_snake_case` or `scope::(_)varname_2`)
-- `(_)namespace_Macroname`
+- **macros**: camel case (`(_)GoodMacroname`)
-- `(_)NAMESPACE_SYMBOLNAME` for constant symbols
+- **constants** (eg. in ROM): upper case (`scope::(_)NICE_SYMBOLNAME`)
-- `(_)NAMESPACE_symbolname` for variables

main.s65

@@ -2,6 +2,7 @@
 .code
 
 .macro DEBUG_LED_OFF nr
+    pha
     lda IO1 + IO::RA
 .if nr = 0
     and #%11111110
@@ -9,9 +10,11 @@
     and #%11111101
 .endif
     sta IO1 + IO::RA
+    pla
 .endmacro
 
 .macro DEBUG_LED_ON nr
+    pha
     lda IO1 + IO::RA
 .if nr = 0
     ora #%00000001
@@ -19,6 +22,7 @@
     ora #%00000010
 .endif
     sta IO1 + IO::RA
+    pla
 .endmacro
 
 ;********************************************************************************    
@@ -37,6 +41,7 @@ SPI_IO = IO2
 ; Printer
     .include "programs/printer.s65"
     .include "programs/print_slow.s65"
+    .include "programs/spi-menu.s65"
 ; Digital Humidity and Temerature Sensor
     ; .include "dht.s65"
 
@@ -61,8 +66,8 @@ irq:
     lda IO2+IO::IFR
     sta IRQ_VAR
     bbr7 IRQ_VAR,@irq_return
-    bbs1 IRQ_VAR,@irq_keypad  ; check CB1
     bbs2 IRQ_VAR,@irq_spi_p  ; check SR
+    bbs1 IRQ_VAR,@irq_keypad  ; check CA1
     ; this should never be reached
     jsr lcd_clear
     Print str_irq_unknown
@@ -75,7 +80,7 @@ irq:
     jsr kp_read_on_irq
     bra @irq_return
 @irq_spi_p:
-    jsr spi_p_read
+    jsr spi_p::read
     bra @irq_return
 ; @irq_dht:
 ;     lda IO1 + IO::T1CL ;T1L2  ; clear interrupt flag
@@ -89,14 +94,15 @@ irq:
 reset:
     jsr lcd_init
 
+    ; TODO debug stuff
+    stz IO2 + IO::DDRB
     lda #$ff
     sta IO1 + IO::DDRA
     DEBUG_LED_OFF 0
     DEBUG_LED_OFF 1
 
-    jsr kp_init
 
-    jsr spi_p_init
+    jsr kp_init
 
 
     ; ; INIT DHT
@@ -112,48 +118,61 @@ reset:
 
     ; enable interrupts
     cli
- 
+    bra home
-.proc return_home
-    Print message_menu
-.endproc
 
 .proc home
-    jsr rb_keypad_read
+    Print message_menu
-    beq home
+    ; jsr rb_keypad_read
+@loop:
+    lda _KP_DEBUG_VAL
+    beq @loop
+    ; TODO debug
+    sta 0
+    stz _KP_DEBUG_VAL
+    lda 0
     ; beq home
     cmp #'A'
     jeq printer
     cmp #'B'
-    jeq SPI_CODE_START
+    jeq spi_menu::spi_menu
-    ; jeq dht_request
     cmp #'C'
     jeq print_1
     cmp #'D'
     jeq print_2
-    cmp #'0'
+    cmp #'1'
-    bne @l1
+    beq @debug0_on
-    DEBUG_LED_OFF 0
+    cmp #'2'
-    jmp home
+    beq @debug0_off
-@l1:
+    cmp #'4'
-    cmp #'#'
+    beq @debug1_on
-    bne @l2
+    cmp #'5'
-    DEBUG_LED_ON 0
+    beq @debug1_off
-    jmp home
+    cmp #'7'
-@l2:
+    beq @print_rb
-    cmp #'8'
-    bne @l3
-    DEBUG_LED_OFF 1
-    jmp home
-@l3:
-    cmp #'9'
-    bne @l4
-    DEBUG_LED_ON 1
-    jmp home
-@l4:
     cmp #'*'  ; print home menu again if not visible (message 1 and 2 jmp to home)
-    jeq return_home
+    beq home
+    jmp @loop
     
-    jmp home
+@debug0_off:
+    DEBUG_LED_OFF 0
+    jmp @loop
+@debug0_on:
+    DEBUG_LED_ON 0
+    jmp @loop
+@debug1_off:
+    DEBUG_LED_OFF 1
+    jmp @loop
+@debug1_on:
+    DEBUG_LED_ON 1
+    jmp @loop
+@print_rb:
+    jsr lcd_clear
+    Print str_io2
+    lda IO2 + IO::RB
+    jsr lcd_char
+    lda #'''
+    jsr lcd_char
+    jmp @loop
 .endproc
 
 
@@ -181,13 +200,19 @@ message_2:
 message_menu: 
     .byte   "<A> Printer     "
     ; .byte   "<B> Temperatur  "
-    .byte   "<B> Run from SPI"
+    .byte   "<B> SPI-Menu    "
     .byte   "<C> Text 1      "
     .asciiz "<D> Text 2      "
+str_spi_begin:
+    .asciiz "---BEGIN  SPI---"
+str_spi_start:
+    .asciiz "---START  SPI---"
 str_irq:
     .asciiz "IRQ detected!   "
 str_irq_unknown:
     .asciiz "Unknown IRQ src!"
+str_io2:
+    .asciiz "IO2::RB='"
 
 ;********************************************************************************
 ; reset vector

programs/memcopy.s65

@@ -12,8 +12,8 @@ INCLUDE_MEMCOPY = 1
     cpy
 loop:
     beq @loop_end
-    lda (ARG0,y)
+    lda (ARG0),y
-    sta (ARG2,y)
+    sta (ARG2),y
     dey
     bra @loop
 loop_end:

programs/print_slow.s65

@@ -33,9 +33,9 @@ INCLUDE_PRINT_SLOW = 1
 ;********************************************************************************
 .macro PrintSlow message,time_cs
     jsr lcd_clear
-    lda #.LOBYTE(message)
+    lda #<message
     sta ARG0
-    lda #.HIBYTE(message)
+    lda #>message
     sta ARG1
     phx
     ldx #time_cs

programs/printer.s65

@@ -10,7 +10,7 @@ printer:
     jsr rb_keypad_read
     beq @printer_loop
     cmp #'*'
-    jeq return_home
+    jeq home
     jsr lcd_char
     bra @printer_loop
 .endif  ; guard

programs/spi-menu.s65

@@ -0,0 +1,92 @@
+.include "system/spi.s65"
+.include "util/string.s65"
+.ifndef INCLUDE_SPI_MENU
+INCLUDE_SPI_MENU = 1
+
+.scope spi_menu
+.bss
+trans_bytes: .res 1
+trans_pages: .res 1
+status:      .res 1
+status_str:  .res 17  ; 16 + null
+
+.code
+.proc spi_menu
+    stz trans_bytes
+    stz trans_pages
+    lda #'X'
+    sta status
+@print_menu:
+    jsr lcd_clear
+    Print MENU
+@print_status:
+    Strf FMT_STATUS,status_str,trans_pages,trans_bytes,status
+    lda #(LCD_CMD_SET_ADDRESS | LCD_LINE4)
+    jsr _lcd_cmd
+    Print status_str
+@loop:
+    ; check if a byte has been transferred
+@check_byte:
+    lda spi_p::bytes_written
+    cmp trans_bytes
+    bne @byte_written
+@check_page:
+    lda spi_p::pages_written
+    cmp trans_pages
+    bne @page_written
+    bra @read_keypad
+@byte_written:
+    sta trans_bytes
+    bra @print_status
+@page_written:
+    sta trans_pages
+    bra @print_status
+
+@read_keypad:
+    lda _KP_DEBUG_VAL
+    beq @loop
+    ; TODO debug
+    sta 0
+    stz _KP_DEBUG_VAL
+    lda 0
+    cmp #'*'
+    beq @return_home
+    cmp #'A'
+    beq @spi_begin
+    cmp #'B'
+    beq @spi_end
+    cmp #'C'
+    beq @spi_jump
+    bra @loop
+@spi_begin:
+    lda #'@'
+    sta status
+    jsr spi_p::begin
+    jmp @print_menu
+@spi_end:
+    lda #'X'
+    sta status
+    jsr spi_p::end
+    jmp @print_menu
+@spi_jump:
+    jsr spi_p::end
+    jsr lcd_clear
+    Print START
+    jmp spi_p::SPI_CODE_START
+@return_home:
+    jsr spi_p::end
+    jmp home
+.endproc
+
+.rodata 
+MENU:
+    .byte   "A> Beg. Transfer"
+    .byte   "B> Stop Transfer"
+    .asciiz "C> Jump  Home <*"
+    ; .asciiz "0b0p   Status: X"
+FMT_STATUS: .asciiz "%x%xb  Status:%x"
+BEGIN:      .asciiz "---BEGIN  SPI---"
+START:      .asciiz "---START  SPI---"
+
+.endscope
+.endif  ; guard

system/io_W65C22.h65

@@ -102,25 +102,5 @@ INCLUDE_IOW65C22 = 1
     IRQ  = %10000000
 .endenum
 
-    ; TODO: leave?
+.endscope ; IO
-    ; .struct VIA_Pins
+.endif  ; guard
-    ;     RB   .byte   ; $0
-    ;     RA   .byte   ; $1
-    ;     DDRB .byte   ; $2
-    ;     DDRA .byte   ; $3
-    ;     T1CL .byte   ; $4
-    ;     T1CH .byte   ; $5
-    ;     T1LL .byte   ; $6
-    ;     T1LH .byte   ; $7
-    ;     T2CL .byte   ; $8
-    ;     T2CH .byte   ; $9
-    ;     SR   .byte   ; $a
-    ;     ACR  .byte   ; $b
-    ;     PCR  .byte   ; $c
-    ;     IFR  .byte   ; $d
-    ;     IER  .byte   ; $e
-    ;     RANH .byte   ; $f  ; no handshake
-    ; .endstruct
-.endif
-.endscope
-

system/keypad.s65

@@ -18,6 +18,7 @@ INCLUDE_KEYPAD = 1
 
 .zeropage
 _KP_COLUMN:         .res 1  ; for storing stuff
+_KP_DEBUG_VAL:      .res 1  ; for storing the last char DEBUG
 
 .bss  ; reserve space or ringbuffer
 KP_BUF_SIZE = 10
@@ -90,6 +91,8 @@ RBUF_MEM_END = RBUF_MEM_START + KP_BUF_SIZE - 1
     rts
 @kp_write:
     lda _KP_VALUES,x
+    ; TODO use ringbuffer
+    sta _KP_DEBUG_VAL
     jsr rb_keypad_write
     rts
 .endproc
@@ -97,9 +100,9 @@ RBUF_MEM_END = RBUF_MEM_START + KP_BUF_SIZE - 1
 .rodata
 _KP_VALUES:
     .byte "174*"
-    .byte "396#"
     .byte "2850"
-    .byte "ABCD"
+    .byte "396#"
+    .byte "ACBD"
     ; keypad conencted so that 
     ; row 1 = PA0
     ; row 2 = PA2

system/spi.s65

@@ -10,30 +10,148 @@
 
 .ifndef INCLUDE_SPI
 INCLUDE_SPI = 1
+.scope spi_p
 
 
+.zeropage
+code_page:          .res 2  ; SPI_CODE_START + pages_written * 256
 .bss
-SPI_PAGES_WRITTEN:  .res 1
+bytes_written:      .res 1
-SPI_BYTES_WRITTEN:  .res 1
+pages_written:      .res 1
+
+.include "util/math.s65"
+; spi-transferred code will be placed here
 .segment "SPI"
-SPI_CODE_START:     ; .res $1000
+SPI_CODE_START:
-    lda $1000
+    lda '$'
-    sta $1000
+    jsr lcd_char
-    lda $1000
+    lda #<TEST_FMT
-    sta $1000
+    sta ARG0
-    lda $1000
+    lda #>TEST_FMT
-    sta $1000
+    sta ARG1
+    lda #<TEST_OUT
+    sta ARG2
+    lda #>TEST_OUT
+    sta ARG3
+    lda #$a9
+    sta ARG4
+    lda #$3c
+    sta ARG5
+    lda #$10
+    sta ARG6
+    jsr strf
+    Print TEST_OUT
+@spiloop:
     lda IO1 + IO::RA
-    lda IO1 + IO::RA
+    lda IO2 + IO::RA
-    bra SPI_CODE_START
+    nop
-    ; jsr lcd_clear
+    bra @spiloop
-    ; PrintSlow msg,20
+    jmp home
-    ; jmp home
+
-; msg:
+; TODO allocate zp memory
-    ; .asciiz "YO DAS WAR    SPI"
+fmt_idx = $30
+out_idx = $31
+;********************************************************************************
+; @function Format a string
+; @details
+;   If there is no value to be read, the Pz will be set
+;   Formats:
+;   - u: unsigned decimal integer (1 byte)
+;   - U: unsigned decimal integer (2 bytes)
+; @param ARG0-1: Format string address
+; @param ARG2-3: Output string address
+; @param ARG4+:  Additional parameters
+; @returns 
+; @modifies: A, Y
+;********************************************************************************
+.proc strf
+    stz out_idx
+    stz fmt_idx
+    ldy #0  ; position in string
+    ldx #0  ; index of format args
+@loop:
+    ldy fmt_idx
+    lda (ARG0),y
+    beq @null
+    cmp #'%'
+    beq @percent
+@normal_char:  ; store A in output string
+        ldy out_idx
+        sta (ARG2),y
+        inc fmt_idx
+        inc out_idx
+        beq @out_overflow
+        bra @loop
+@percent:  ; check for format in next position
+        iny
+        sty fmt_idx
+        lda (ARG0),y
+        beq @null
+        ; formats
+        cmp #'x'
+        beq @format_hex1
+        bra @normal_char
+@format_hex1:   ; 1 byte hex -> 2 chars
+            lda ARG4,x
+            phx
+            jsr int8_to_hex_str
+            ldy out_idx
+            sta (ARG2),y  ; most sig digit
+            iny
+            beq @out_overflow
+            txa
+            sta (ARG2),y  ; least sig digit
+            iny
+            beq @out_overflow
+            sty out_idx
+            plx
+            inx  ; 1 byte of args handeled
+            ; bra @format_return
+@format_return:  ; increment fmt_idx to swallow the formating char
+        inc fmt_idx
+        bra @loop
+@out_overflow:  ; store 0 in last position
+    ldy #$ff
+    sty out_idx
+@store_null:
+    lda #0
+@null:  ; store and return
+    ldy out_idx
+    sta (ARG2),y
+@rts:
+    rts
+.endproc
+
+
+;********************************************************************************
+; @function Convert a 1 byte number into two hex characters
+; @param A: Number to convert
+; @returns A: Most significant digit
+; @returns X: Least significant digit
+; @modifies X,Y,A
+;********************************************************************************
+.proc int8_to_hex_str
+    pha
+    and #%00001111
+    tay
+    ldx HEX_CHARS,y
+    pla
+    div A,16
+    and #%00001111
+    tay
+    lda HEX_CHARS,y
+    rts
+.endproc
     
     
 
+
+HEX_CHARS: .byte "0123456789ABCDEF"
+
+TEST_FMT: .asciiz "%x -> %x -> %x:)"
+TEST_OUT: .asciiz "TESTOUT"
+
+; SPI_P = as peripheral
 .code
 .struct SPI_P_Pins
     ; VIA addresses
@@ -50,12 +168,20 @@ SPI_CODE_START:     ; .res $1000
 .endstruct
 
 ;********************************************************************************
-; @function Initialize the IO Adapter for SPI
+; @function Begin listening for SPI transfers
-; @param ARG0-1 Address of the SPI_Pins struct
+; @details
+;   - initialize variables
+;   - configure shift register to shift in under external clock
+;   - enable shift register interrupts 
 ;********************************************************************************
-.proc spi_p_init
+.proc begin
-    stz SPI_PAGES_WRITTEN
+    stz pages_written
-    stz SPI_BYTES_WRITTEN
+    stz bytes_written
+    ; store address in zp
+    lda #<SPI_CODE_START
+    sta code_page
+    lda #>SPI_CODE_START
+    sta code_page + 1
     ; todo USE MASKS
     ; set Shift register to shift in under external clock on CB1
     lda #IO::ACR::SR_SIN_PHIE
@@ -64,21 +190,49 @@ SPI_CODE_START:     ; .res $1000
     ; enable SR interrupts
     lda #(IO::IRQ::IRQ | IO::IRQ::SR)
     sta SPI_IO + IO::IER
-    DEBUG_LED_ON 1
+
+    ; load SR to reset
+    lda SPI_IO + IO::SR
     rts
 .endproc
 
-.proc spi_p_read
+;********************************************************************************
-    DEBUG_LED_ON 0
+; @function Stop listening for SPI transfers
-    ; print received byte
+; @details
+;  Disables shift register interrupts
+;********************************************************************************
+.proc end
+    ; disable SR interrupts
+    lda #IO::IRQ::SR
+    sta SPI_IO + IO::IER
+    rts
+.endproc
+    
+
+
+;********************************************************************************
+; @function Read a byte from SPI
+; @details
+;  Reads a byte from the shift register and stores it in the SPI code buffer
+;********************************************************************************
+.proc read
+    ldx bytes_written
     lda SPI_IO + IO::SR
     sta SPI_CODE_START,x
-    inc SPI_BYTES_WRITTEN
+    inc bytes_written
-    jsr lcd_char
+    beq @new_page
+    rts
+@new_page:
+    inc pages_written
+    inc code_page + 1
     rts
 .endproc
 
     
+;********************************************************************************
+; @function Initialize the IO Adapter for SPI
+; @param ARG0-1 Address of the SPI_Pins struct
+;********************************************************************************
 ;********************************************************************************
 ; @function Read bytes
 ; @param X Number of bytes to send
@@ -96,8 +250,8 @@ SPI_CODE_START:     ; .res $1000
 .proc send_data
 .endproc
 
+.endscope
 
     
-_send_byte:
 
 .endif

util/math.s65

@@ -0,0 +1,106 @@
+;********************************************************************************
+; @module math
+; @type utility
+; @details
+;   Math library
+;********************************************************************************
+.ifndef INCLUDE_MATH
+INCLUDE_MATH = 1
+
+.scope math
+
+;********************************************************************************
+; @macro Divide a num (or A) by a factor
+; @param num: Memory or A
+; @param divider: must be power of 2
+;********************************************************************************
+.macro div num,divider
+.if divider = 2
+    lsr num
+.elseif divider = 4
+    lsr num
+    lsr num
+.elseif divider = 8
+    lsr num
+    lsr num
+    lsr num
+.elseif divider = 16
+    .repeat 4
+    lsr num
+    .endrepeat
+.elseif divider = 32
+    .repeat 5
+    lsr num
+    .endrepeat
+.elseif divider = 64
+    .repeat 6
+    lsr num
+    .endrepeat
+.elseif divider = 128
+    .repeat 7
+    lsr num
+    .endrepeat
+.else
+    .error "div macro: divider % 2 != 0"
+.endif
+.endmacro
+
+; .macro Amult1 factor
+;     phx
+;     ldx factor
+;     AmultX
+;     plx
+; .endmacro
+
+; https://www.llx.com/Neil/a2/mult.html
+; .macro mult num1,num2,result
+;     lda #0
+;     ldx #8
+; L1: 
+;     lsr num2
+;     bcc L2
+;     clc
+;     adc num1
+; L2:
+;     ror
+;     ror result
+;     dex
+;     bne L1
+;     sta result+1
+; .endmacro
+
+;         00110101
+;         10010011
+;         -------^
+;        =00110101
+;        00110101
+;        01001001
+;        -------^
+;       =00110101
+;       00110101
+;       00100100
+;       -------^
+;      =00000000
+;      00110101
+;      00010010
+;      -------^
+;     =00000000
+;     00110101
+;     00001001
+;     -------^
+;     00110101
+;    00110101
+;    00000100
+;    -------^
+;   =00000000
+;   00110101
+;   00000010
+;   -------^
+;  =00000000
+;  00110101
+;  00000001
+; 00110101
+
+      
+.endscope
+.endif  ; guard

util/string.s65

@@ -0,0 +1,163 @@
+;********************************************************************************
+; @module string
+; @type utility
+; @details
+;   String utility
+;********************************************************************************
+.ifndef INCLUDE_STRING
+INCLUDE_STRING = 1
+
+.scope str
+
+.code
+.macro _StrfStoreArg arg
+.if (.not .blank(arg))
+    .if .match(arg, x)
+        stx ARG4 + @N_ARGS
+    .elseif .match(arg, y)
+        sty ARG4 + @N_ARGS
+    .else
+        lda arg
+        sta ARG4 + @N_ARGS
+    .endif
+    @N_ARGS .set (@N_ARGS + 1)
+.endif
+.endmacro
+
+;********************************************************************************
+; @function Macro for passing arguments to strf
+; @param fmt:   Format string address
+; @param out:   Output string address
+; @param x0-x9: Additional parameters
+; @warning Addresses as additional paramteres must be passed like this `#<addr,#>addr`
+; @modifies: A, X, Y
+; @see strf
+;********************************************************************************
+.macro Strf fmt,out,x0,x1,x2,x3,x4,x5,x6,x7,x8,x9
+    @N_ARGS .set 0  ; @ so that it doesnt break cheap labels
+    lda #<fmt
+    sta ARG0
+    lda #>fmt
+    sta ARG1
+    lda #<out
+    sta ARG2
+    lda #>out
+    sta ARG3
+    _StrfStoreArg x0
+    _StrfStoreArg x1
+    _StrfStoreArg x2
+    _StrfStoreArg x3
+    _StrfStoreArg x4
+    _StrfStoreArg x5
+    _StrfStoreArg x6
+    _StrfStoreArg x7
+    jsr strf
+    .out .sprintf("info: Strf: called with %d arguments", @N_ARGS)
+.endmacro
+
+; TODO allocate zp memory
+fmt_idx = $30
+out_idx = $31
+;********************************************************************************
+; @function Format a string
+; @details
+;   If there is no value to be read, the Pz will be set
+;   Formats:
+;   - x: unsigned hex integer (1 byte) -> 2 chars
+;   - X: unsigned hex integer (2 byte) -> 4 chars TODO
+;   - u: unsigned decimal integer (1 byte) TODO
+;   - U: unsigned decimal integer (2 bytes) TODO
+; @param ARG0-1: Format string address
+; @param ARG2-3: Output string address
+; @param ARG4+:  Additional parameters
+; @returns 
+; @modifies: A, X, Y
+;********************************************************************************
+.proc strf
+    stz out_idx
+    stz fmt_idx
+    ldy #0  ; position in string
+    ldx #0  ; index of format args
+@loop:
+    ldy fmt_idx
+    lda (ARG0),y
+    beq @null
+    cmp #'%'
+    beq @percent
+@normal_char:  ; store A in output string
+        ldy out_idx
+        sta (ARG2),y
+        inc fmt_idx
+        inc out_idx
+        beq @out_overflow
+        bra @loop
+@percent:  ; check for format in next position
+        iny
+        sty fmt_idx
+        lda (ARG0),y
+        beq @null
+        ; formats
+        cmp #'x'
+        beq @format_hex1
+        bra @normal_char
+@format_hex1:   ; 1 byte hex -> 2 chars
+            lda ARG4,x
+            phx
+            jsr int8_to_hex_str
+            ldy out_idx
+            sta (ARG2),y  ; most sig digit
+            iny
+            beq @out_overflow
+            txa
+            sta (ARG2),y  ; least sig digit
+            iny
+            beq @out_overflow
+            sty out_idx
+            plx
+            inx  ; 1 byte of args handeled
+            ; bra @format_return
+@format_return:  ; increment fmt_idx to swallow the formating char
+        inc fmt_idx
+        bra @loop
+@out_overflow:  ; store 0 in last position
+    ldy #$ff
+    sty out_idx
+@store_null:
+    lda #0
+@null:  ; store and return
+    ldy out_idx
+    sta (ARG2),y
+@rts:
+    rts
+.endproc
+
+
+;********************************************************************************
+; @function Convert a 1 byte number into two hex characters
+; @param A: Number to convert
+; @returns A: Most significant digit
+; @returns X: Least significant digit
+; @modifies A,X,Y
+;********************************************************************************
+.proc int8_to_hex_str
+    pha
+    and #%00001111
+    tay
+    ldx HEX_CHARS_UPPER,y
+    pla
+    div A,16
+    and #%00001111
+    tay
+    lda HEX_CHARS_UPPER,y
+    rts
+.endproc
+
+
+.rodata
+HEX_CHARS_UPPER:    .byte "0123456789ABCDEF"
+HEX_CHARS_LOWER:    .byte "0123456789abcdef"
+
+.export strf
+
+.endscope
+.endif  ; guard