From fd9ccdbce47d6d3ca1527626249f80e3689bb617 Mon Sep 17 00:00:00 2001
From: Byron Lathi <bslathi19@gmail.com>
Date: Tue, 28 Nov 2023 22:54:26 -0800
Subject: [PATCH] Add serial driver and irq support

---
 sw/kernel/devices/sd_card.c      | 12 +++-
 sw/kernel/devices/serial.h       | 17 ++++++
 sw/kernel/devices/serial.s       | 94 ++++++++++++++++++++++++++++++++
 sw/kernel/interrupts/interrupt.s |  4 +-
 sw/kernel/kernel.c               | 15 ++++-
 5 files changed, 135 insertions(+), 7 deletions(-)
 create mode 100644 sw/kernel/devices/serial.h
 create mode 100644 sw/kernel/devices/serial.s

diff --git a/sw/kernel/devices/sd_card.c b/sw/kernel/devices/sd_card.c
index 8eaf708..4dd6a4e 100644
--- a/sw/kernel/devices/sd_card.c
+++ b/sw/kernel/devices/sd_card.c
@@ -339,12 +339,16 @@ token = 0xFF - response timeout
 *******************************************************************************/
 uint8_t SD_writeSingleBlock(uint32_t addr, uint8_t *buf, uint8_t *token)
 {
+
+    (void)addr;
+    (void)buf;
+    (void)token;
+
+    /*
     uint16_t readAttempts;
     uint8_t res1, read;
     uint16_t i;
 
-    /*
-
     // set token to none
     *token = 0xFF;
 
@@ -391,9 +395,11 @@ uint8_t SD_writeSingleBlock(uint32_t addr, uint8_t *buf, uint8_t *token)
     spi_deselect(0);
     spi_exchange(0xFF);
 
+    return res1;
+
     */
 
-    return res1;
+    return 0;
 }
 
 /*******************************************************************************
diff --git a/sw/kernel/devices/serial.h b/sw/kernel/devices/serial.h
new file mode 100644
index 0000000..2f85df4
--- /dev/null
+++ b/sw/kernel/devices/serial.h
@@ -0,0 +1,17 @@
+#ifndef _SERIAL_H
+#define _SERIAL_H
+
+#include <stdint.h>
+
+void serial_handle_irq();
+
+void serial_init();
+
+void serial_putc(char c);
+void serial_puts(char* s);
+
+
+char serial_getc();
+char serial_getc_nb();
+
+#endif
\ No newline at end of file
diff --git a/sw/kernel/devices/serial.s b/sw/kernel/devices/serial.s
new file mode 100644
index 0000000..0203826
--- /dev/null
+++ b/sw/kernel/devices/serial.s
@@ -0,0 +1,94 @@
+.MACPACK generic
+
+.autoimport
+
+.import _enable_irq, _send_eoi, _uart_txb_block
+
+.importzp tmp1, ptr1
+
+.export _serial_init
+.export _serial_handle_irq
+
+.export _serial_putc, _serial_puts, _serial_getc, _serial_get_nb
+
+.zeropage
+
+last_char: .res 1
+
+
+.code
+
+UART        = $efe6
+UART_TXB    = UART
+UART_RXB    = UART
+UART_STATUS = UART + 1
+
+; Initialize Serial Port
+; No initialization needed, just register irq handler.
+.proc _serial_init
+        lda #<_serial_handle_irq
+        ldx #>_serial_handle_irq
+        jsr pushax
+        lda #$01
+        jsr _register_irq
+        stz last_char
+        rts
+.endproc
+
+; Serial Port IRQ Handler
+; Get the character and store it.
+.proc _serial_handle_irq
+        lda UART_RXB
+        sta last_char
+        ora #$80        ; set msb
+        jsr _send_eoi
+        rti
+.endproc
+
+; Serial Port Get Character
+; If a character has not been received, block until one is.
+.proc _serial_getc
+L1:     lda last_char
+        bpl L1
+        and #$7f
+        sta last_char
+        rts
+.endproc
+
+; Serial Port Get Character Non-Blocking
+; return last character, even if it has already been read.
+; If the character is new, we still clear the new flag.
+.proc _serial_get_nb
+        lda last_char
+        bpl L1
+        and #$7f
+        sta last_char
+L1:     rts
+.endproc
+
+
+; Serial Port Put Character
+; send a single character over the serial port.
+.proc _serial_putc
+        jsr _uart_txb_block
+        cmp #$0a
+        bne @1
+        lda #$0d
+        jsr _uart_txb_block
+@1:     rts
+.endproc
+
+; Send a string over the serial port. Needs stlen
+.proc _serial_puts
+        sta ptr1                ; Store pointer in ptr1
+        stx ptr1+1  
+        ldy #$00                ; initialize y to 0
+L1:     lda (ptr1),y            ; load character from string
+        beq L2                  ; Quit if NULL
+        jsr _uart_txb_block      ; send character (does not change y or ptr1)
+        iny                     ; increment y
+        bne L1                  ; If Y == 0, increment high byte of pointer
+        inc ptr1+1
+        bne L1                  ; if high byte wraps around, give up
+L2:     rts
+.endproc
\ No newline at end of file
diff --git a/sw/kernel/interrupts/interrupt.s b/sw/kernel/interrupts/interrupt.s
index 0344b0a..ede0000 100644
--- a/sw/kernel/interrupts/interrupt.s
+++ b/sw/kernel/interrupts/interrupt.s
@@ -48,7 +48,7 @@ rti
     sta IRQ_CMD_ADDR
     lda IRQ_DAT_ADDR
     ; shift by 2 (oh so only 128 interrupts are supported lol)
-    lsr
+    asl
     tax
     jmp (irq_table,x)
     ; use that to index jump table
@@ -56,6 +56,7 @@ rti
 
 ; void register_irq(void* addr, uint8_t irqn);
 .proc _register_irq
+    asl
     tax
     jsr popa
     sta irq_table,x
@@ -65,6 +66,7 @@ rti
     lda #$00
     jsr pusha
     txa
+    lsr
     jsr _enable_irq
     rts
 .endproc
diff --git a/sw/kernel/kernel.c b/sw/kernel/kernel.c
index 6441fb3..6870a2e 100644
--- a/sw/kernel/kernel.c
+++ b/sw/kernel/kernel.c
@@ -3,6 +3,7 @@
 #include "interrupts/interrupt.h"
 #include "devices/mapper.h"
 #include "devices/rtc.h"
+#include "devices/serial.h"
 
 
 void handle_rtc_interrupt() {
@@ -14,6 +15,8 @@ void handle_rtc_interrupt() {
 
 int main() {
 
+    uint8_t c;
+
     cputs("Kernel\n");
 
     cputs("Init Mapper\n");
@@ -32,9 +35,15 @@ int main() {
 
     asm volatile("cli");
 
-    // cputs("Initialize Serial\n");
-    // // init_serial();
-    // enable_irq(2, IRQ_EDGE);
+    cputs("Initialize Serial\n");
+    serial_init();
+
+    serial_puts("Hello from serial!\n");
+
+    c = serial_getc();
+
+    serial_puts("Got a character!: ");
+    serial_putc(c);
 
     while(1);