Change serial port peripheral to match SPIM registers definition.

Still Tx only and keep 0xffffc000 base to allows single
instruction LW and SW access.

Signed-off-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>

3 files changed, 61 insertions, 14 deletions

diff --git a/README.md b/README.md
index 7235409..66ed7e5 100644
--- a/README.md
+++ b/README.md
@@ -90,19 +90,29 @@ Peripherals
 The simulator implements emulation of two peripherals for now.
 
 The firs is simple serial port (UART) which transmission
-(Tx) support only for now. It provides two registers, the
-first is status port. Bit 0 is reserved for notification
-that UART is busy and cannot accept next character.
-The second register is actual Tx buffer. The LSB byte
-of writtent word is transmitted to terminal window.
-Definition of peripheral base address and registers
-offsets follows.
-
+(Tx) support only for now. Actual version implements only
+two registers, the 'SERP_TX_ST_REG' is trasmit status register.
+Bit 0 signals by value 1 that UART is ready and can
+accept next character to be sent.
+The second register 'SERP_TX_DATA_REG' is actual Tx buffer.
+The LSB byte of writtent word is transmitted to terminal
+window. Definition of peripheral base address and registers
+offsets follows including reserve for the future Rx port
+implementation.
 ```
 #define SERIAL_PORT_BASE   0xffffc000
-#define SERP_ST_REG_o            0x00
-#define SERP_ST_REG_TX_BUSY_m     0x1
-#define SERP_TX_REG_o            0x04
+
+#define SERP_RX_ST_REG_o           0x00
+#define SERP_RX_ST_REG_READY_m      0x1
+#define SERP_RX_ST_REG_IE_m         0x2
+
+#define SERP_RX_DATA_REG_o         0x04
+
+#define SERP_TX_ST_REG_o           0x08
+#define SERP_TX_ST_REG_READY_m      0x1
+#define SERP_TX_ST_REG_IE_m         0x2
+
+#define SERP_TX_DATA_REG_o         0x0c
 ```
 
 The another peripheral allows to set three byte values
diff --git a/qtmips_machine/serialport.cpp b/qtmips_machine/serialport.cpp
index 0fc0ad2..9e4177b 100644
--- a/qtmips_machine/serialport.cpp
+++ b/qtmips_machine/serialport.cpp
@@ -35,10 +35,23 @@
 
 #include "serialport.h"
 
+#define SERP_RX_ST_REG_o           0x00
+#define SERP_RX_ST_REG_READY_m      0x1
+#define SERP_RX_ST_REG_IE_m         0x2
+
+#define SERP_RX_DATA_REG_o         0x04
+
+#define SERP_TX_ST_REG_o           0x08
+#define SERP_TX_ST_REG_READY_m      0x1
+#define SERP_TX_ST_REG_IE_m         0x2
+
+#define SERP_TX_DATA_REG_o         0x0c
+
 using namespace machine;
 
 SerialPort::SerialPort() {
-
+    rx_st_reg = 0;
+    tx_st_reg = 0;
 }
 
 SerialPort::~SerialPort() {
@@ -52,9 +65,19 @@ bool SerialPort::wword(std::uint32_t address, std::uint32_t value) {
 #endif
     emit write_notification(address, value);
 
-    if (address == 0x04)
+    switch (address) {
+    case SERP_RX_ST_REG_o:
+        rx_st_reg &= ~SERP_RX_ST_REG_IE_m;
+        rx_st_reg |= value & SERP_RX_ST_REG_IE_m;
+        break;
+    case SERP_TX_ST_REG_o:
+        tx_st_reg &= ~SERP_TX_ST_REG_IE_m;
+        tx_st_reg |= value & SERP_TX_ST_REG_IE_m;
+        break;
+    case SERP_TX_DATA_REG_o:
         emit tx_byte(value & 0xff);
-
+        break;
+    }
     return true;
 }
 
@@ -65,6 +88,17 @@ std::uint32_t SerialPort::rword(std::uint32_t address, bool debug_access) const
     printf("SerialPort::rword address 0x%08lx\n",
            (unsigned long)address);
 #endif
+    switch (address) {
+    case SERP_RX_ST_REG_o:
+        value = rx_st_reg;
+        break;
+    case SERP_RX_DATA_REG_o:
+        value = 0;
+        break;
+    case SERP_TX_ST_REG_o:
+        value = tx_st_reg | SERP_TX_ST_REG_READY_m;
+        break;
+    }
 
     emit read_notification(address, &value);
 
diff --git a/qtmips_machine/serialport.h b/qtmips_machine/serialport.h
index 2b14a7e..add1fe6 100644
--- a/qtmips_machine/serialport.h
+++ b/qtmips_machine/serialport.h
@@ -58,6 +58,9 @@ signals:
 public:
     bool wword(std::uint32_t address, std::uint32_t value);
     std::uint32_t rword(std::uint32_t address, bool debug_access = false) const;
+private:
+    std::uint32_t rx_st_reg;
+    std::uint32_t tx_st_reg;
 };
 
 }