From 7092cc8f77947159976133e17a85e60fdefc9a02 Mon Sep 17 00:00:00 2001
From: Byron Lathi <bslathi19@gmail.com>
Date: Sun, 10 Apr 2022 17:55:51 -0500
Subject: [PATCH] Add SD card software interface

Adds a function to send a command to the sd card.
---
 sw/io.inc65  |  3 +++
 sw/main.c    |  4 ++++
 sw/sd_card.h |  8 ++++++++
 sw/sd_card.s | 27 +++++++++++++++++++++++++++
 4 files changed, 42 insertions(+)
 create mode 100644 sw/sd_card.h
 create mode 100644 sw/sd_card.s

diff --git a/sw/io.inc65 b/sw/io.inc65
index 5e87bc2..3586e7c 100644
--- a/sw/io.inc65
+++ b/sw/io.inc65
@@ -11,4 +11,7 @@ SW          = LED
 MM_CTRL		= $7ff7
 MM_DATA		= $7fe0
 
+SD_ARG      = $7ff8
+SD_CMD      = $7ffc
+
 IRQ_STATUS  = $7fff
diff --git a/sw/main.c b/sw/main.c
index 4f894d8..aea99c8 100644
--- a/sw/main.c
+++ b/sw/main.c
@@ -4,6 +4,7 @@
 #include "board_io.h"
 #include "uart.h"
 #include "mapper.h"
+#include "sd_card.h"
 
 int main() {
     int i;
@@ -46,6 +47,9 @@ int main() {
 	cprintf("Reading from 0x4000: %x\n", *(unsigned int*)(0x4000));
 	cprintf("Reading from 0x5000: %x\n", *(unsigned int*)(0x5000));
 
+	sd_card_command(0, 0);
+	sd_card_command(0x000001aa, 8);
+
     while (1) {
 
         sw = sw_read();
diff --git a/sw/sd_card.h b/sw/sd_card.h
new file mode 100644
index 0000000..1cd59af
--- /dev/null
+++ b/sw/sd_card.h
@@ -0,0 +1,8 @@
+#ifndef _SD_CARD_H
+#define _SD_CARD_H
+
+#include <stdint.h>
+
+void sd_card_command(uint32_t arg, uint8_t cmd);
+
+#endif
\ No newline at end of file
diff --git a/sw/sd_card.s b/sw/sd_card.s
new file mode 100644
index 0000000..f6c6ed6
--- /dev/null
+++ b/sw/sd_card.s
@@ -0,0 +1,27 @@
+.include "io.inc65"
+
+.importzp sp, sreg
+
+.export _sd_card_command
+
+.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