stuff

boot.asm

@@ -1,12 +1,13 @@
 STACK_TOP = 0xFFFF
-; At 500 kHz the CPU has about 500 T-states per millisecond.
+; At 1 MHz the CPU has about 1000 T-states per millisecond.
 ; The inner delay loop below costs about 26 T-states per taken iteration:
 ;   dec hl  =  6T
 ;   ld a,h  =  4T
 ;   or l    =  4T
 ;   jr nz   = 12T
-; 500 / 26 = 19.2, so 20 iterations is the nearest simple whole-number choice.
+; 1000 / 26 = 38.5. Use 40 iterations to retain the previous calibration,
-DELAY_LOOPS_PER_MS = 20
+; which used 20 iterations at 500 kHz.
+DELAY_LOOPS_PER_MS = 40
 
         .globl _main
         .globl _delay_ms
@@ -99,7 +100,7 @@ _io_in::
 
 ; Approximate millisecond delay.
 ; Input: HL = delay in milliseconds.
-; For CLK_SPEED = 500000 Hz this uses 20 inner iterations per ms.
+; For CLK_SPEED = 1000000 Hz this uses 40 inner iterations per ms.
 _delay_ms::
         ld      a, h
         or      l

main.c

@@ -1,117 +1,65 @@
 #include "boot.h"
 
-/*
+#define VID_CMD    0x80
- * 6850 ACIA test wiring assumption:
+#define VID_DAT    0x81
- *   /CS2 is driven by not-A5, so the ACIA is selected when A5 = 1.
+#define VID_CMD_SET_TEXT_MODE       0
- *   RS is assumed to be wired to A0, giving:
+#define VID_CMD_SET_PIXEL_MODE      1
- *     0x20 = status/control
+#define VID_CMD_CLR                 2
- *     0x21 = data
+#define VID_CMD_TEXT_POS_X          3
- */
+#define VID_CMD_TEXT_POS_Y          5
-#define ACIA_CTRL_STATUS 0x20
+#define VID_CMD_PIXEL_POS_X         4
-#define ACIA_DATA        0x21
+#define VID_CMD_PIXEL_POS_Y         6
 
-#define ACIA_STATUS_RDRF 0x01
+void putc(char c){
-#define ACIA_STATUS_TDRE 0x02
+    io_out(VID_DAT, c);
-
-#define ACIA_CMD_MASTER_RESET 0x03
-#define ACIA_CMD_8N1_DIV1     0x14
-
-/*
- * Z80 CTC wiring assumption:
- *   /CE is driven by not-A4, so use 0x10 as the base address.
- *   A0 and A1 select channels 0 through 3.
- */
-#define CTC_CHANNEL_0          0x10
-#define CTC_CHANNEL_1          0x11
-#define CTC_CHANNEL_2          0x12
-#define CTC_CHANNEL_3          0x13
-
-#define CTC_CMD_RESET          0x03
-#define CTC_CMD_COUNTER_RISING 0x4F
-#define CTC_TEST_TIME_CONSTANT 52
-
-static void acia_init(void)
-{
-    io_out(ACIA_CTRL_STATUS, ACIA_CMD_MASTER_RESET);
-    io_out(ACIA_CTRL_STATUS, ACIA_CMD_8N1_DIV1);
 }
 
-static void ctc_init(void)
+void puts(char * s){
-{
+    while(*s){
-    /* Leave unused channels in reset. */
+        putc(*s);
-    io_out(CTC_CHANNEL_1, CTC_CMD_RESET);
+        s++;
-    io_out(CTC_CHANNEL_2, CTC_CMD_RESET);
-    io_out(CTC_CHANNEL_3, CTC_CMD_RESET);
-
-    /*
-     * Channel 0: counter mode, rising-edge trigger, no interrupt. CLK/TRG0
-     * must be connected to the 500 kHz clock.  Writing the time constant
-     * starts the counter, and ZC/TO0 produces a pulse at:
-     *
-     *     500000 / 52 = 9615.4 Hz
-     *
-     * This is the closest integer division to 9600 Hz (about +0.16%).
-     */
-    io_out(CTC_CHANNEL_0, CTC_CMD_COUNTER_RISING);
-    io_out(CTC_CHANNEL_0, CTC_TEST_TIME_CONSTANT);
-}
-
-static uint8_t acia_status(void)
-{
-    return io_in(ACIA_CTRL_STATUS);
-}
-
-static void acia_putc(uint8_t value)
-{
-    while ((acia_status() & ACIA_STATUS_TDRE) == 0) {
-    }
-    io_out(ACIA_DATA, value);
-}
-
-static uint8_t acia_getc_nonblocking(uint8_t *value)
-{
-    if ((acia_status() & ACIA_STATUS_RDRF) == 0) {
-        return 0;
-    }
-
-    *value = io_in(ACIA_DATA);
-    return 1;
-}
-
-static void acia_puts(const char *text)
-{
-    while (*text) {
-        acia_putc((uint8_t)*text++);
     }
 }
 
 void main(void)
 {
-    uint8_t cnt = 0;
+    delay_ms(100);
-    uint8_t ch = 0;
-
-    io_out(PIO_A_CTRL, 0x0F);
-    io_out(PIO_A_DATA, 0x00);
-
-    ctc_init();
-    acia_init();
-    acia_puts("ACIA 6850 test ready\r\n");
 
     for(;;){
-        uint8_t status = acia_status();
+        io_out(VID_CMD, VID_CMD_TEXT_POS_X);
+        io_out(VID_DAT, 0);
+        io_out(VID_CMD, VID_CMD_TEXT_POS_Y);
+        io_out(VID_DAT, 0);
+        io_out(VID_CMD, VID_CMD_SET_TEXT_MODE);
+        io_out(VID_CMD, VID_CMD_CLR);
 
-        if (acia_getc_nonblocking(&ch)) {
+
-            io_out(PIO_A_DATA, ch);
+        for(uint8_t i=0; i<18; i++){
-            acia_putc(ch);
+            putc('0'+i);
-            if (ch == '\r') {
+            puts("\r\n");
-                acia_putc('\n');
-            }
-            delay_ms(50);
         }
 
-        acia_putc((uint8_t)('0' + (cnt & 0x07)));
+        delay_ms(2000);
-        acia_puts("\r\n");
+
-        cnt++;
+
-        delay_ms(250);
+        io_out(VID_CMD, VID_CMD_SET_PIXEL_MODE);
+        io_out(VID_CMD, VID_CMD_CLR);
+
+        for(uint8_t y=0; y<255; y++){
+            uint16_t py = 160 + y;
+            uint16_t px = 256;
+
+            io_out(VID_CMD, VID_CMD_PIXEL_POS_X);
+            io_out(VID_DAT, px&0xff);
+            io_out(VID_DAT, px>>8);
+            io_out(VID_CMD, VID_CMD_PIXEL_POS_Y);
+            io_out(VID_DAT, py&0xff);
+            io_out(VID_DAT, py>>8);
+            io_out(VID_CMD, VID_CMD_SET_PIXEL_MODE);
+            for(uint8_t x=0; x<32; x++)
+                io_out(VID_DAT, 0xff);
+        }
+
+        delay_ms(2000);
     }
 }