gios: initialize uart, flush uart

src/asm/gios/bootstrap.S

@@ -9,10 +9,21 @@ loop:
     jzre done
     jre loop
 done:
-    .ldsrc greeting
-    .lddst uart_send_string
+    .lddst uart_init        ; initialize uart
+    puship
     jmpdst
+
+    .ldsrc greeting         ; write greeting to uart
+    .lddst uart_send_string 
+    puship
+    jmpdst
+
+    .lddst uart_flush       ; wait until flushed
+    puship
+    jmpdst
+
     halt
+
 ;
 ; ROM data
 ;

src/asm/gios/ports.S

@@ -8,6 +8,10 @@ UART_0_RBR:
 .global UART_0_THR
 UART_0_THR:
 
+.org 0x2013
+.global UART_0_LCR
+UART_0_LCR:
+
 .org 0x2015
 .global UART_0_LSR
 UART_0_LSR:

src/asm/gios/serial.S

+.global uart_init
 .global uart_send_byte
 .global uart_send_string
+.global uart_flush
+
+uart_init:
+    .ldsrc UART_0_LCR
+    .lddst UART_0_LCR
+    ld r0               ; set DLAB
+    imm r1, 0b10000000
+    or r0, r1
+    st r0
+
+    .lddst UART_0_RBR   ; set DLL
+    imm r2, 4
+    st r2
+
+    .lddst UART_0_THR   ; set DLM
+    imm r2, 0
+    st r2
+
+    neg r1              ; reset DLAB
+    .lddst UART_0_LCR
+    and r0, r1
+    st r0
+
+    pop r6              ; ret
+    pop r7
+    jmpdst
 
 ; send the byte in r0 to the uart
 ; if the transmit register is not empty, waits for it to become empty
@@ -29,8 +56,9 @@ uart_send_string:
 
     push r4
     push r5
+    .lddst uart_send_byte
     puship
-    jre uart_send_byte
+    jmpdst
     pop r5
     pop r4
 
@@ -46,3 +74,16 @@ _uart_send_string_done:
     pop r7
     jmpdst
 
+; wait until uart is finished (TEMT=1)
+;
+uart_flush:
+    .ldsrc UART_0_LSR   ; load LSR
+    ld r0
+    imm r1, 0b01000000  ; bit6 = TEMT
+    and r0, r1
+    jzre uart_flush     ; loop until TEMT = 1
+
+    pop r6
+    pop r7
+    jmpdst              ; ret
+