From 75b5488b8d217c1d602bc4646e99e9af053107a8 Mon Sep 17 00:00:00 2001
From: Paul Mathieu <paulmathieu@google.com>
Date: Sat, 13 Mar 2021 15:49:28 -0800
Subject: [PATCH] uart: upgrade C api

---
 uart/echo.c    |  6 ++++--
 uart/ledctrl.c |  4 +++-
 uart/uart.c    | 20 ++++++++++----------
 uart/uart.h    | 17 ++++++++++-------
 4 files changed, 27 insertions(+), 20 deletions(-)

diff --git a/uart/echo.c b/uart/echo.c
index 4d78baf..9cfb9b3 100644
--- a/uart/echo.c
+++ b/uart/echo.c
@@ -1,9 +1,11 @@
 #include "uart.h"
 
+#define uart0 ((struct uart*)0xc010)
+
 int main() {
   while (1) {
-    char c = uart_read();
-    uart_write(c);
+    char c = uart_read(uart0);
+    uart_write(uart0, c);
   }
 
   // never returns
diff --git a/uart/ledctrl.c b/uart/ledctrl.c
index 38fdddd..c5c49fb 100644
--- a/uart/ledctrl.c
+++ b/uart/ledctrl.c
@@ -1,13 +1,15 @@
 #include "led.h"
 #include "uart.h"
 
+#define uart0 ((struct uart*)0xc010)
+
 int main() {
   int c;
   int led = 0;
 
   while (1) {
     led_write(1 << led);
-    c = uart_read();
+    c = uart_read(uart0);
 
     if (c == 'a') {
       led++;
diff --git a/uart/uart.c b/uart/uart.c
index debb0b7..098d8de 100644
--- a/uart/uart.c
+++ b/uart/uart.c
@@ -1,23 +1,23 @@
 #include "uart.h"
 
-int uart_rx_available() {
-  return (*UART_STATUS & UART_STATUS_RXNE_msk) != 0;
+int uart_rx_available(struct uart* uart) {
+  return uart->flags & UART_STATUS_RXNE_msk != 0;
 }
 
-int uart_tx_available() {
-  return (*UART_STATUS & UART_STATUS_TXE_msk) != 0;
+int uart_tx_available(struct uart* uart) {
+  return uart->flags & UART_STATUS_TXE_msk != 0;
 }
 
-void uart_write(const char c) {
-  while (!uart_tx_available()) {
+void uart_write(struct uart* uart, const char c) {
+  while (!uart_tx_available(uart)) {
   }
 
-  *UART_DATA = c;
+  uart->data = c;
 }
 
-char uart_read() {
-  while (!uart_rx_available()) {
+char uart_read(struct uart* uart) {
+  while (!uart_rx_available(uart)) {
   }
 
-  return *UART_DATA;
+  return uart->data;
 }
diff --git a/uart/uart.h b/uart/uart.h
index 726691d..e5266af 100644
--- a/uart/uart.h
+++ b/uart/uart.h
@@ -1,13 +1,16 @@
-#define UART_BASE 0xc010
-#define UART_DATA   ((volatile char*) (UART_BASE + 0x00))
-#define UART_STATUS ((volatile char*) (UART_BASE + 0x02))
+#pragma once
 
 #define UART_STATUS_RXNE_pos 1
 #define UART_STATUS_RXNE_msk (1 << UART_STATUS_RXNE_pos)
 #define UART_STATUS_TXE_pos  0
 #define UART_STATUS_TXE_msk  (1 << UART_STATUS_TXE_pos)
 
-int uart_rx_available();
-int uart_tx_available();
-void uart_write(const char c);
-char uart_read();
+struct uart {
+  volatile uint8_t data;
+  volatile uint16_t flags;
+};
+
+int uart_rx_available(struct uart* uart);
+int uart_tx_available(struct uart* uart);
+void uart_write(struct uart* uart, const char c);
+char uart_read(struct uart* uart);