Separate kernel code from test code

Eventually I want the kernel to be loaded from the SD card as well, but
it still needs to separate from user programs.

At some point there should be a folder just for the BIOS, which should
read from the boot block of the SD card and start executing, and thats
it.

sw/kernel/devices/sd_card_asm.s

@@ -0,0 +1,66 @@
+.include "io.inc65"
+
+.importzp sp, sreg, ptr1
+
+.export _sd_card_command
+.export _sd_card_resp
+.export _sd_card_read_byte
+.export _sd_card_wait_for_data
+
+.autoimport on
+
+.code
+
+; Send sd card command.
+; command is in A register, the args are on the stack
+; I think the order is high byte first?
+_sd_card_command:
+    pha
+
+    jsr popeax
+    sta SD_ARG
+    stx SD_ARG+1
+    lda sreg
+    sta SD_ARG+2
+    lda sreg+1
+    sta SD_ARG+3
+
+    pla
+    sta SD_CMD
+    rts
+
+; void sd_card_resp(uint32_t* resp);
+_sd_card_resp:
+        phy
+        sta ptr1        ; store pointer
+        stx ptr1+1
+@1:     lda SD_CMD      ; wait for status flag
+        and #$01
+        beq @1
+        lda SD_ARG
+        ldy #$0
+        sta (ptr1),y
+        lda SD_ARG+1
+        iny
+        sta (ptr1),y
+        lda SD_ARG+2
+        iny
+        sta (ptr1),y
+        lda SD_ARG+3
+        iny
+        sta (ptr1),y
+        ply
+        rts
+
+_sd_card_read_byte:
+        lda SD_DATA
+        ldx #$00
+        rts
+
+_sd_card_wait_for_data:
+        pha
+@1:     lda SD_CMD      ; wait for status flag
+        and #$02
+        beq @1
+        pla
+        rts