SD_command assembly rewrite

sw/bootloader/devices/sd_card.c

@@ -94,6 +94,7 @@ void SD_powerUpSeq()
 /*******************************************************************************
  Send command to SD card
 *******************************************************************************/
+/*
 void SD_command(uint8_t cmd, uint32_t arg, uint8_t crc)
 {
     // transmit command to sd card
@@ -108,6 +109,7 @@ void SD_command(uint8_t cmd, uint32_t arg, uint8_t crc)
     // transmit crc
     spi_exchange(crc|0x01);
 }
+*/
 
 /*******************************************************************************
  Read R1 from SD card

sw/bootloader/devices/sd_card_asm.s

@@ -0,0 +1,32 @@
+.export _SD_command
+
+.importzp sp
+
+.autoimport on
+
+; void SD_command(uint8_t cmd, uint32_t arg, uint8_t crc)
+
+; The plan: push crc to stack, load arg into tmp1 through 4
+
+.proc   _SD_command:    near
+
+        pha                     ; Push CRC to cpu stack
+        ldy     #$04
+        lda     (sp),y          ; Load CMD
+        ora     #$40            ; start bit
+        jsr     _spi_exchange
+
+        dey
+arg_loop:                       ; send ARG
+        lda     (sp),y
+        jsr     _spi_exchange      
+        dey
+        bpl     arg_loop
+
+        pla                     ; Pull CRC from stack
+        ora     #$01            ; stop bit
+        jsr     _spi_exchange
+        jsr     incsp5          ; pop all off stack
+        rts
+
+.endproc