From e3faeb080ba0f4e965ba47a1a1f4847042d595f6 Mon Sep 17 00:00:00 2001
From: Aki <please@ignore.pl>
Date: Sat, 10 Jul 2021 23:14:26 +0200
Subject: Moved keyboard updates to one spot

---
 lc3.c | 64 +++++++++++++++++++++++++++++++++++++++-------------------------
 1 file changed, 39 insertions(+), 25 deletions(-)

diff --git a/lc3.c b/lc3.c
index 6740b48..3dedc7d 100644
--- a/lc3.c
+++ b/lc3.c
@@ -131,33 +131,22 @@ uint16_t check_key()
 	FD_ZERO(&fds);
 	FD_SET(0, &fds);
 	tv.tv_sec = 0;
-	tv.tv_sec = 0;
+	tv.tv_usec = 0;
 	const int r = select(1, &fds, NULL, NULL, &tv);
 	die(r, "check_key select()");
 	return 0 != r;
 }
 
+void update_keyboard()
+{
+	uint8_t c;
+	ssize_t r = read(0, &c, 1);
+	die(r, "read_memory read()");
+	memory[MEMORY_KBDR] = (uint16_t) c;
+}
+
 uint16_t read_memory(const uint16_t address)
 {
-	if (MEMORY_KBSR == address)
-	{
-		if (check_key())
-		{
-			memory[MEMORY_KBSR] |= 1u << 15;
-			uint8_t c;
-			ssize_t r = read(0, &c, 1);
-			die(r, "read_memory read()");
-			memory[MEMORY_KBDR] = (uint16_t) c;
-		}
-		else
-		{
-			memory[MEMORY_KBSR] &= ~(1u << 15);
-		}
-	}
-	else if (MEMORY_DSR == address)
-	{
-		memory[MEMORY_DSR] = 1u << 15;
-	}
 	return memory[address];
 }
 
@@ -189,13 +178,31 @@ void fire(const uint16_t interrupt, const uint16_t priority)
 
 void write_memory(const uint16_t address, const uint16_t value)
 {
-	if (MEMORY_DDR == address)
+	switch (address)
 	{
-		uint8_t c = (uint8_t) value;
-		ssize_t r = write(1, &c, 1);
-		die(r, "write_memory write()");
+		case MEMORY_KBSR:
+		{
+			memory[MEMORY_KBSR] &= 0x8000;
+			memory[MEMORY_KBSR] |= value & 0x7fff;
+			break;
+		}
+		case MEMORY_KBDR:
+		case MEMORY_DSR:
+		{
+			break;
+		}
+		case MEMORY_DDR:
+		{
+			uint8_t c = (uint8_t) value;
+			ssize_t r = write(1, &c, 1);
+			die(r, "write_memory write()");
+		} // fallthrough
+		default:
+		{
+			memory[address] = value;
+			break;
+		}
 	}
-	memory[address] = value;
 }
 
 void update_cond(const uint16_t reg)
@@ -494,6 +501,7 @@ int main(int argc, char ** argv)
 	signal(SIGINT, handle_signal);
 	atexit(restore_terminal);
 	prepare_terminal();
+	memory[MEMORY_DSR] = 0x8000;
 	registers[REGISTER_PC] = MEMORY_USER;
 	registers[REGISTER_PSR] |= FLAG_SUP;
 	registers[REGISTER_SSP] = MEMORY_USER;
@@ -503,7 +511,13 @@ int main(int argc, char ** argv)
 		step(instruction);
 		if (check_key())
 		{
+			update_keyboard();
 			fire(0x80, 4);
+			memory[MEMORY_KBSR] |= 0x8000;
+		}
+		else
+		{
+			memory[MEMORY_KBSR] &= 0x7fff;
 		}
 	}
 }
-- 
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