Add some basic fat32 code

sw/kernel/devices/io.inc65

@@ -10,4 +10,21 @@ SPI_BAUD    = $efd8
 SPI_INPUT   = $efd9
 SPI_OUTPUT  = $efda
 SPI_CTRL    = $efdb
-SPI_STATUS  = SPI_CTRL
+SPI_STATUS  = SPI_CTRL
+
+MULTIPLIER_BASE = $eff0
+
+MULTIPLIER_AL = MULTIPLIER_BASE + 0
+MULTIPLIER_AH = MULTIPLIER_BASE + 1
+MULTIPLIER_BL = MULTIPLIER_BASE + 2
+MULTIPLIER_BH = MULTIPLIER_BASE + 3
+
+MULTIPLIER_OLL = MULTIPLIER_BASE + 4
+MULTIPLIER_OLH = MULTIPLIER_BASE + 5
+MULTIPLIER_OHL = MULTIPLIER_BASE + 6
+MULTIPLIER_OHH = MULTIPLIER_BASE + 7
+
+GOLDEN_OUTPUT_0 = $03
+GOLDEN_OUTPUT_1 = $0a
+GOLDEN_OUTPUT_2 = $08
+GOLDEN_OUTPUT_3 = $00

sw/kernel/devices/multiplier.h

@@ -0,0 +1,12 @@
+#ifndef _MULTIPLER_H
+#define _MULTIPLER_H
+
+#include <stdint.h>
+
+/* Multiply 2 integers into 1 long */
+uint32_t lmulii(uint16_t a, uint16_t b);
+
+/* Multiply 2 integers into 1 integer, discarding upper bits. */
+uint16_t imulii(uint16_t a, uint16_t b);
+
+#endif

sw/kernel/devices/multiplier.s

@@ -0,0 +1,36 @@
+.include "io.inc65"
+
+.MACPACK generic
+
+.import popax
+.importzp sreg
+
+.export _lmulii, _imulii
+
+.code
+
+.proc _lmulii
+    sta MULTIPLIER_BL
+    stx MULTIPLIER_BH
+    jsr popax
+    sta MULTIPLIER_AL
+    stx MULTIPLIER_AH
+    lda MULTIPLIER_OHL
+    sta sreg
+    lda MULTIPLIER_OHH
+    sta sreg+1
+    lda MULTIPLIER_OLL
+    ldx MULTIPLIER_OLH
+    rts
+.endproc
+
+.proc _imulii
+    sta MULTIPLIER_BL
+    stx MULTIPLIER_BH
+    jsr popax
+    sta MULTIPLIER_AL
+    stx MULTIPLIER_AH
+    lda MULTIPLIER_OLL
+    ldx MULTIPLIER_OLH
+    rts
+.endproc