From cfebe5feb55777bb377ff310b8cde03f3e0c25ff Mon Sep 17 00:00:00 2001
From: Christian Cunningham <cc@localhost>
Date: Fri, 4 Feb 2022 00:05:50 -0700
Subject: Access Uart through rotating buffer

---
 include/drivers/uart.h |  3 +++
 src/cpu/irq.c          |  3 +++
 src/drivers/uart.c     | 38 ++++++++++++++++++++++++++++++++++++++
 src/sys/core.c         |  1 +
 4 files changed, 45 insertions(+)

diff --git a/include/drivers/uart.h b/include/drivers/uart.h
index b83732f..1491f20 100644
--- a/include/drivers/uart.h
+++ b/include/drivers/uart.h
@@ -9,6 +9,9 @@ extern void uart_char(unsigned char c);
 extern void uart_string(char* message);
 extern void uart_hex(unsigned long data);
 
+void uart_init();
+void* uart_print(char*);
+void uart_flush(void);
 void uart_10(unsigned long);
 void uart_hexn(unsigned long);
 
diff --git a/src/cpu/irq.c b/src/cpu/irq.c
index 2197067..15603b9 100644
--- a/src/cpu/irq.c
+++ b/src/cpu/irq.c
@@ -84,6 +84,9 @@ unsigned long c_fiq_handler(void)
 		if (counter % 0x6000 == 0) {
 			counter = 0;
 		}
+		if (counter % 0x8 == 0) {
+			add_thread(uart_flush, 0, 5);
+		}
 		if (counter % 0x30 == 0) {
 			return 1;
 		} 
diff --git a/src/drivers/uart.c b/src/drivers/uart.c
index f6fe79b..c5514ce 100644
--- a/src/drivers/uart.c
+++ b/src/drivers/uart.c
@@ -1,5 +1,43 @@
 #include <drivers/uart.h>
 
+#define UART_BUFFER_SIZE 0x100
+struct UartBuffer {
+	char buffer[UART_BUFFER_SIZE];
+	unsigned long roffset;
+	unsigned long woffset;
+} ubuffer;
+
+void uart_init(void)
+{
+	ubuffer.roffset = 0;
+	ubuffer.woffset = 0;
+}
+
+// s = zero-terminated string
+void* uart_print(char* s)
+{
+	char* ptr = s;
+	while (1) {
+		if (*ptr == 0)
+			break;
+		ubuffer.buffer[ubuffer.woffset] = *ptr;
+		if ((ubuffer.woffset+1)%UART_BUFFER_SIZE == ubuffer.roffset)
+			return ptr;
+		ubuffer.woffset++;
+		ubuffer.woffset %= UART_BUFFER_SIZE;
+		ptr += 1;
+	}
+	return 0;
+}
+
+void uart_flush(void)
+{
+	while (ubuffer.roffset != ubuffer.woffset) {
+		uart_char(ubuffer.buffer[ubuffer.roffset++]);
+		ubuffer.roffset %= UART_BUFFER_SIZE;
+	}
+}
+
 void uart_10(unsigned long val)
 {
 	unsigned long t = val;
diff --git a/src/sys/core.c b/src/sys/core.c
index b29412f..d761336 100644
--- a/src/sys/core.c
+++ b/src/sys/core.c
@@ -28,6 +28,7 @@ void sysinit(void)
 	stimeh = *(unsigned long*)SYS_TIMER_CHI;
 	stimel = *(unsigned long*)SYS_TIMER_CLO;
 	*(unsigned long*) SYS_TIMER_C0 = 60000000 + stimeh; // 60 second trigger
+	uart_init();
 	///...
 
 	// Route GPU interrupts to Core 0
-- 
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