From 2786ec0940b534f138ffc77ef06948ef7d602e27 Mon Sep 17 00:00:00 2001
From: Byron Lathi <bslathi19@gmail.com>
Date: Sat, 16 Apr 2022 14:56:41 -0500
Subject: [PATCH] Execute code read from the SD card

This will read the data from the sd card, copy it to the originally
linked address (no relocation), then execute it.

I am lazy and wrote it in C using weird function pointer casting but
this would probably be more efficient if it were to be written in
assembly instead.

The test program simply returns 'A', but that is enough to prove that it
is actually running.
---
 sw/main.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/sw/main.c b/sw/main.c
index 99ba2d0..08b05fa 100644
--- a/sw/main.c
+++ b/sw/main.c
@@ -1,5 +1,6 @@
 #include <stdint.h>
 #include <conio.h>
+#include <string.h>
 
 #include "board_io.h"
 #include "uart.h"
@@ -79,7 +80,15 @@ int main() {
 
 	o65_header_t* header;
 	o65_opt_t* o65_opt;
+	uint8_t* seg_ptr;
 
+	uint16_t code_base;
+	uint16_t data_base;
+	uint16_t code_len;
+	uint16_t data_len;
+
+	uint8_t (*exec)(void);
+	uint8_t ret;
 
 	uint16_t reserved_count;
 	uint32_t sectors_per_fat;
@@ -222,6 +231,12 @@ int main() {
 		cprintf("stack: %x\n", header->stack);
 		cprintf("\n");
 
+		code_base = header->tbase;
+		data_base = header->dbase;
+		code_len = header->tlen;
+		data_len = header->dlen;
+
+
 		o65_opt = (o65_opt_t*)(buf + sizeof(o65_header_t));
 		while (o65_opt->olen)
 		{
@@ -246,6 +261,48 @@ int main() {
 			cprintf("\n\n");
 			o65_opt = (o65_opt_t*)((uint8_t*)o65_opt + o65_opt->olen);
 		}
+
+		seg_ptr = (uint8_t*)o65_opt + 1;
+
+		cprintf("Code: \n");
+		for (i = 0; i < code_len; i++) {
+			cprintf("%x ", seg_ptr[i]);
+		}
+		cprintf("\n\n");
+
+		memcpy((uint8_t*)code_base, seg_ptr, code_len);
+
+		seg_ptr+=code_len;
+
+		cprintf("Data: \n");
+		for (i = 0; i < data_len; i++) {
+			cprintf("%x ", seg_ptr[i]);
+		}
+		cprintf("\n\n");
+
+		memcpy((uint8_t*)data_base, seg_ptr, data_len);
+
+		cprintf("Memory Copied!\n");
+		cprintf("Code: \n");
+		for (i = 0; i < code_len; i++) {
+			cprintf("%x ", ((uint8_t*)code_base)[i]);
+		}
+		cprintf("\n\n");
+		cprintf("Data: \n");
+		for (i = 0; i < data_len; i++) {
+			cprintf("%x ", ((uint8_t*)data_base)[i]);
+		}
+		cprintf("\n\n");
+
+		exec = (int(*)(void))code_base;
+
+		ret = 0;
+
+		ret = (*exec)();
+
+		cprintf("ret: %x\n", ret);
+
+
 	}