Add some nifty shit to stdio.s.

Adds print and fread functions, both of which read NUL-terminated
strings. print writes them using the character output device, and
fread reads them from the block device to a region of memory.

README

@@ -66,13 +66,13 @@ Extensions to the 6502 instruction set
 
 I/O memory map:
 
-    There are three I/O devices right now: a character input
-    device, a character output device and a virtual
-    terminal. Convenience constants and macros for the
-    character I/O devices are defined in `stdlib/stdio.s'
-    for use in user programs. Add stdlib to your include
-    path and then add `#include <stdio.s>' to your program
-    to use these constants.
+    There are four I/O devices right now: a character input
+    device, a character output device, a virtual terminal
+    and a block device. Convenience constants and macros for
+    the character I/O devices are defined in
+    `stdlib/stdio.s' for use in user programs. Add stdlib to
+    your include path and then add `#include <stdio.s>' to
+    your program to use these constants.
 
     I/O options are controlled by setting bits on the I/O
     flag byte at address 0xFF02. The current set of
@@ -141,6 +141,18 @@ I/O devices:
     sample_programs/echo.s, and an example of a vterm
     application is provided in sample_programs/spam.s
 
+    A block device can be mapped in with control addresses
+    at 0xFF03 through 0xFF07. To use the block device, you
+    must specify a binary disk image to back the device
+    using the -d flag. To read from the block device, write
+    an address in the disk image to 0xFF03 and 0xFF04, with
+    the low byte in 0xFF03. The value at that location in
+    the disk image will be written to 0xFF05, which your
+    program can then read. To write, set the memory address
+    to write to using the same method, then write the
+    desired byte to 0xFF06. If any of these operations
+    return an error, the byte at 0xFF07 will be nonzero.
+
 Reading the source
 
     x6502 was written to be easy to understand and read. A

main.c

@@ -52,8 +52,8 @@ int main(int argc, char *argv[]) {
         return -1;
     }
 
-    debugf("using %s as a backing file for block device 0\n", blck0_file);
     if (blck0_file != NULL) {
+        debugf("using %s as a backing file for block device 0\n", blck0_file);
         FILE *blck0 = fopen(blck0_file, "r+");
         if (blck0 == NULL) {
             fprintf(stderr, "block file %s does not exist.\n", blck0_file);

sample_programs/README

@@ -1,6 +1,6 @@
 Test 6502 assembler programs. Generate binaries with:
 
-xa -w -bt 0x0100 -Istdlib/ sample_programs/test.s
+xa -w -Istdlib/ sample_programs/test.s
 
 xa is a cross-assembler and utility suite for 65xx series processors. It's
 included in many package repositories as `xa65', including Homebrew on OSX in
@@ -20,3 +20,5 @@ Sample programs:
         spam.s          Writes A through Z repeatedly, filling the vterm.
                         Demonstrates vterm output and how to do indirect
                         addressing to address the whole vterm.
+        stdlib_test.s   Demo program displaying the functionality of the
+                        standard library.

sample_programs/diskread/gendisk.c

@@ -8,7 +8,10 @@ int main() {
         printf("could not open file, err: %s", strerror(errno));
         return 1;
     }
-    fprintf(f, "hello, world!");
+    fprintf(f, "hello, world, from disk!\n");
+    fputc(0, f);
+    fseek(f, 0xFF00, SEEK_SET);
+    fprintf(f, "hello from a seeked position.\n");
     fclose(f);
     return 0;
 }

sample_programs/stdlib_test.s

@@ -0,0 +1,26 @@
+#include <stdio.s>
+
+    lda     #$02    ; set WAIT_TERMINATE flag
+    sta     iomode
+    lda     #<str
+    sta     $F0
+    lda     #>str
+    sta     $F1
+    jsr     print
+
+    lda     #$00
+    sta     blck0_addrl
+    sta     blck0_addrh
+    jsr     fread
+    jsr     print
+
+    lda     #$00
+    sta     blck0_addrl
+    lda     #$FF
+    sta     blck0_addrh
+    jsr     fread
+    jsr     print
+
+    ext
+
+str: .asc "hello, world, from .data!", $0A, $00

stdlib/stdio.s

@@ -1,11 +1,81 @@
-; defines useful constants for writing 6502 assembler that targets x6502
-
-putc = $FF00
-getc = $FF01
-iomode = $FF02
-paint = $FEE8
+; defines useful constants and methods for writing 6502 assembler that targets x6502
 
 #define debug .byt $FC
 #define ext .byt $FF
 #define DEBUG debug
 #define EXT ext
+
+.(
+jmp prog
+
++putc = $FF00
++getc = $FF01
++iomode = $FF02
++paint = $FEE8
+
++blck0_addrl = $FF03
++blck0_addrh = $FF04
++blck0_read = $FF05
++blck0_write = $FF06
++blck0_err = $FF07
+
+; print reads two bytes from $00F0, treats them as a memory address, then
+; reads from that memory address and prints those characters to the character
+; device until a NUL character is found. the printed string must be less than
+; 256 characters long.
++print:
+.(
+    pha
+    ldy     #$00
+loop:
+    lda     ($F0),Y
+    cmp     #$00
+    beq     done
+    sta     putc
+    iny
+    ; check that y hasn't overflowed
+    cpy     #$00
+    beq     done
+    jmp     loop
+done:
+    pla
+    rts
+.)
+
+; fread reads up to 255 bytes into a memory region that starts at the address in
+; $00F0 from the current position of the block device until a null character is
+; encountered.
++fread:
+.(
+    pha
+    ldy     #$00
+
+loop:
+    lda     blck0_read
+    ; TODO check read status
+
+    sta     ($F0),Y
+
+    iny
+    ; check that y hasn't overflowed
+    cpy     #$00
+    beq     done
+
+    ; increment disk address, using carry addition
+    clc
+    lda     #$01
+    adc     blck0_addrl
+    sta     blck0_addrl
+    lda     #$00
+    adc     blck0_addrh
+    sta     blck0_addrh
+
+    jmp     loop
+
+done:
+    pla
+    rts
+.)
+
+prog:
+.)