Keyboard input, hex printer

README.md

@@ -24,7 +24,11 @@ Hello world programs that run without an operating system.
     1.  [reboot](reboot.S)
     1.  [Not testable in userland](not-testable-in-userland.md)
         1.  [Segment registers real mode](segment_registers_real_mode.S)
-            1 [SS (TODO)](ss.S)
+            1.  [SS (TODO)](ss.S)
+        1.  [Interrupt](interrupt.S)
+            1.  [Interrupt zero divide](interrupt_zero_divide.S)
+        1.  in
+            1.  [in keyboard](in_keyboard.S)
     1.  APM
         1.  [APM shutdown](apm_shutdown.S)
         1.  [APM shutdown 2](apm_shutdown2.S)

TODO.md

@@ -7,7 +7,7 @@
 
 -   instructions
 
-    - wbinvd
+    - cache: wbinvd
     - outb inb
     - lgdtl, paging http://stackoverflow.com/questions/21128311/the-physical-address-of-global-descriptor-table http://stackoverflow.com/questions/7415515/problem-accessing-control-registers-cr0-cr2-cr3
     - lidtl, interrupts, IDTR
@@ -25,6 +25,7 @@
     - http://stackoverflow.com/questions/14480579/when-does-segment-registers-change
     - http://stackoverflow.com/questions/15335003/x86-protected-mode-segment-registers-purpose
     - http://stackoverflow.com/questions/17210620/assembler-calculating-a-memory-address-with-register-base?lq=1
+      http://stackoverflow.com/questions/18736663/what-does-the-colon-mean-in-x86-assembly-gas-syntax-as-in-dsbx
     - http://stackoverflow.com/questions/20717890/how-to-interpret-gs0x14?lq=1
     - http://stackoverflow.com/questions/22446104/do-the-x86-segment-registers-have-special-meaning-usage-on-modern-cpus-and-oses?lq=1
     - http://stackoverflow.com/questions/26058665/fs-register-in-assembly-code?lq=1
@@ -57,8 +58,6 @@
 
 -   ACPI
 
-    -   reboot computer. Would put QEMU into an infinite reboot loop! Awesome. http://stackoverflow.com/questions/32682152/how-to-reboot-in-x86-assembly-from-16-bit-real-mode
-
 -   multithreading: http://stackoverflow.com/questions/7308391/how-is-concurrency-done-in-intel-x86-assembly || http://stackoverflow.com/questions/980999/what-does-multicore-assembly-language-look-like || http://stackoverflow.com/questions/714905/threads-in-x86-assembler-using-the-gnu-assember-as || https://github.com/cirosantilli/oszur11-operating-system-examples/tree/1af6451852887fac3d7206d4d09714c181c81d1e/Chapter_07_Threads
 
 -   play with hardware

bios_carriage_return.S

@@ -13,6 +13,6 @@ Carriage returns are needed just like in old days.
 BEGIN
     PRINT($msg)
     hlt
+END
 msg:
     .asciz "hello\n\rworld"
-END

bios_newline.S

@@ -13,6 +13,6 @@ Carriage returns are needed just like in old days.
 BEGIN
     PRINT($msg)
     hlt
+END
 msg:
     .asciz "hello\nworld"
-END

bios_scroll.S

@@ -36,15 +36,8 @@ which gets filled with the background color in bh.
 #include "common.h"
 BEGIN
 
-/* Print staircase. */
 CLEAR
-PUTC($0x61)
-PUTC($0x0A)
-PUTC($0x62)
-PUTC($0x0A)
-PUTC($0x63)
-PUTC($0x0A)
-PUTC($0x64)
+PRINT($stair)
 
 /* Function ID. */
 mov $0x06, %ah
@@ -70,3 +63,5 @@ int $0x10
 
 hlt
 END
+stair:
+    .asciz "a\nb\nc\nd"

common.h

@@ -50,6 +50,40 @@ Usage: character 'A' (ASCII 61):
     mov c, %al;\
     int $0x10
 
+/*
+Convert a byte to hex ASCII value.
+c: r/m8 byte to be converted
+Output: two ASCII characters, is stored in `al:bl`
+http://stackoverflow.com/questions/3853730/printing-hexadecimal-digits-with-assembly
+*/
+#define HEX(c) GAS_HEX c
+.macro GAS_HEX c
+    mov \c, %al
+    mov \c, %bl
+    shr $4, %al
+    GAS_HEX_NIBBLE al
+    and $0x0F, %bl
+    GAS_HEX_NIBBLE bl
+.endm
+
+/*
+Convert the low nibble of a r8 reg to ASCII of 8-bit in-place.
+reg: r8 to be converted
+Output: stored in reg itself. Letters are uppercase.
+*/
+.macro GAS_HEX_NIBBLE reg
+    LOCAL letter, end
+    cmp $10, %\reg
+    jae letter
+    /* 0x30 == '0' */
+    add $0x30, %\reg
+    jmp end
+letter:
+    /* 0x37 == 'A' - 10 */
+    add $0x37, %\reg
+end:
+.endm
+
 /*
 Print a null terminated string.
 
@@ -65,14 +99,14 @@ We use this `cpp` macro to allow writing `PRINT(S)` with parenthesis.
 #define PRINT(s) GAS_PRINT s
 /* We need a Gas macro for the LOCAL labels. */
 .macro GAS_PRINT s
-    LOCAL halt, loop
+    LOCAL loop, end
     mov s, %si
     mov $0x0e, %ah
 loop:
     lodsb
     or %al, %al
-    jz halt
+    jz end
     int $0x10
     jmp loop
-halt:
+end:
 .endm

in_keyboard.S

@@ -0,0 +1,33 @@
+/*
+Whenever you press a key up or down,
+the keyboard hex scancode is printed to the screen.
+
+Only changes in state are shown.
+
+Scancode tables: TODO: official specs?
+
+- http://flint.cs.yale.edu/cs422/doc/art-of-asm/pdf/APNDXC.PDF
+- https://en.wikipedia.org/wiki/Scancode
+
+TODO Where does the 0x60 come from? http://wiki.osdev.org/I/O_Ports has a small list.
+
+TODO Possible to do this with the interrupt table instead of `in`?
+*/
+
+#include "common.h"
+BEGIN
+    CLEAR
+    /* TODO why CLI makes no difference? We are not using interrupts? */
+    /*cli*/
+loop:
+    in $0x60, %al
+    cmp %al, %cl
+    jz loop
+    mov %al, %cl
+    HEX(<%al>)
+    PUTC(%al)
+    PUTC(%bl)
+    PUTC($0x0A)
+    PUTC($0x0D)
+    jmp loop
+END

interrupt.S

@@ -1,12 +1,11 @@
 /*
 Minimal interrupt example.
 
-Upon division by zero, the interrupt handler is run,
-and it prints the character 'A' to screen.
+Should print the characters 'ab' to screen.
 
 TODO: is STI not needed because this interrupt is not maskable?
 
-TODO: use IDTR. Is initial value guaranteed?
+TODO: use IDTR as a base. Is the initial value 0 guaranteed?
 */
 
 #include "common.h"
@@ -14,11 +13,13 @@ BEGIN
     CLEAR
     movw $handler, 0x00
     movw $0x00, 0x02
-    mov $0x00, %ax
-    div %ax
-    jmp fail
+    int $0
+    PUTC($0x62)
+    jmp end
 handler:
     PUTC($0x61)
-fail:
+    /* Returns to the int instruction. */
+    iret
+end:
     hlt
 END

interrupt_keyboard.S

@@ -1,10 +1,14 @@
 /*
-TODO get working
+TODO get working. Vs `in_keyboard`?
 */
 
 #include "common.h"
 BEGIN
     CLEAR
+    /*
+    I've read that the keyboard handler is the number 1 (second one),
+    and each entry is 4 byte wide.
+    */
     movw $handler, 0x04
     movw $0x00, 0x06
     sti
@@ -12,5 +16,6 @@ loop:
     jmp loop
 handler:
     PUTC($0x61)
+    iret
 jmp loop
 END

interrupt_zero_divide.S

@@ -0,0 +1,17 @@
+/*
+Same as doing an `int $0`.
+*/
+
+#include "common.h"
+BEGIN
+    CLEAR
+    movw $handler, 0x00
+    movw $0x00, 0x02
+    mov $0x00, %ax
+    div %ax
+    jmp fail
+handler:
+    PUTC($0x61)
+fail:
+    hlt
+END

mbr.md

@@ -12,6 +12,8 @@ TODO where is it specified, if at all?
 
 -   BIOS loads the program into memory at the address `0x7C00`.
 
+    Note that this is not the first address that the RIP is set to run: I think all jobs up to now are done by the CPU: the first address seems to be `FFFF:0000` instead: <http://stackoverflow.com/a/32686533/895245>
+
     We must tell that magic number to the linker somehow, either with a linker script, `-tText=-Ttext 0x7C00` or NASM `org 0x7c00`.
 
     This will only matter when you access a memory address, because of relocation.