Add an enable flag for the Videx support

Author: markadev

docs/Usage.md

@@ -4,6 +4,9 @@ After you load on the firmware for your respective Apple II system (II+ or IIe)
 the VGA card is generally plug-and-play. Plug it in, power on your Apple II
 and that's it.
 
+There are some optional features and other controls that can be changed using the
+menu-based Configuration disk or by directly using `POKE` commands.
+
 
 ## Soft Monochrome Mode
 
@@ -56,7 +59,9 @@ This register controls enablement of some features of the card
 
 | bit(s) | Description
 | ------ | -----------
-|  7:2   | reserved
+|  7:4   | reserved
+|   3    | Setting to 1 will disable Videx VideoTerm support (II+ only)
+|   2    | Setting to 1 will enable Videx VideoTerm support (II+ only)
 |   1    | Setting to 1 will disable simulated scanline rendering
 |   0    | Setting to 1 will enable simulated scanline rendering
 

pico/config.c

@@ -7,6 +7,9 @@
 #include "buffers.h"
 #include "colors.h"
 #include "textfont/textfont.h"
+#ifdef APPLE_MODEL_IIPLUS
+#include "videx_vterm.h"
+#endif
 
 
 // A block of flash is reserved for storing configuration persistently across power cycles
@@ -32,11 +35,18 @@ struct config {
 
     // magic word determines if the stored configuration is valid
     uint32_t magic_word;
+
+    // Add new fields after here. When reading the config use the IS_STORED_IN_CONFIG macro
+    // to determine if the field you're looking for is actually present in the stored config.
+
+    uint8_t videx_vterm_enabled;
 };
 
 // This is a compile-time check to ensure the size of the config struct fits within one flash erase sector
 typedef char config_struct_size_check[(sizeof(struct config) <= FLASH_SECTOR_SIZE) - 1];
 
+#define IS_STORED_IN_CONFIG(cfg, field) ((offsetof(struct config, field) + sizeof((cfg)->field)) <= (cfg)->size)
+
 
 extern uint8_t __persistent_data_start[];
 static struct config *cfg = (struct config *)__persistent_data_start;
@@ -54,6 +64,16 @@ void config_load() {
     mono_bg_color = cfg->mono_bg_color;
     mono_fg_color = cfg->mono_fg_color;
     memcpy(character_rom, cfg->character_rom, CHARACTER_ROM_SIZE);
+
+#ifdef APPLE_MODEL_IIPLUS
+    if(IS_STORED_IN_CONFIG(cfg, videx_vterm_enabled)) {
+        if(cfg->videx_vterm_enabled) {
+            videx_vterm_enable();
+        } else {
+            videx_vterm_disable();
+        }
+    }
+#endif
 }
 
 
@@ -63,6 +83,9 @@ void config_load_defaults() {
     mono_bg_color = mono_bg_colors[1];
     mono_fg_color = mono_fg_colors[1];
     memcpy(character_rom, default_character_rom, CHARACTER_ROM_SIZE);
+#ifdef APPLE_MODEL_IIPLUS
+    videx_vterm_disable();
+#endif
 }
 
 
@@ -71,6 +94,7 @@ void config_save() {
     const int new_config_size = (sizeof(struct config) + FLASH_PAGE_SIZE - 1) & -FLASH_PAGE_SIZE;
     struct config *new_config = malloc(new_config_size);
     memset(new_config, 0xff, new_config_size);
+    memset(new_config, 0, sizeof(struct config));
 
     new_config->size = sizeof(struct config);
     new_config->scanline_emulation = soft_scanline_emulation;
@@ -79,6 +103,9 @@ void config_save() {
     new_config->mono_fg_color = mono_fg_color;
     memcpy(new_config->character_rom, character_rom, CHARACTER_ROM_SIZE);
     new_config->magic_word = MAGIC_WORD_VALUE;
+#ifdef APPLE_MODEL_IIPLUS
+    new_config->videx_vterm_enabled = videx_vterm_enabled;
+#endif
 
     const uint32_t flash_offset = (uint32_t)cfg - XIP_BASE;
     flash_range_erase(flash_offset, FLASH_SECTOR_SIZE);

pico/device_regs.c

@@ -5,6 +5,9 @@
 #include "colors.h"
 #include "config.h"
 #include "textfont/textfont.h"
+#ifdef APPLE_MODEL_IIPLUS
+#include "videx_vterm.h"
+#endif
 
 
 static unsigned int char_write_offset;
@@ -18,6 +21,12 @@ void device_write(uint_fast8_t reg, uint_fast8_t data) {
             soft_scanline_emulation = true;
         if(data & 0x02)
             soft_scanline_emulation = false;
+#ifdef APPLE_MODEL_IIPLUS
+        if(data & 0x04)
+            videx_vterm_enable();
+        if(data & 0x08)
+            videx_vterm_disable();
+#endif
         break;
 
     // soft-monochrome color setting
@@ -55,7 +64,7 @@ void device_write(uint_fast8_t reg, uint_fast8_t data) {
 // command value.
 //
 // Note: some of these commands could take a long time (relative to 6502 bus cycles) so
-// some bus activity may be missed. Other projects like the Analog-V2 delegate this execution
+// some bus activity may be missed. Other projects like the V2-Analog delegate this execution
 // to the other (VGA) core to avoid this. Maybe do this if the missed bus cycles become a noticable
 // issue; I only expect it would happen when some config is being saved, which is not done often.
 void execute_device_command(uint_fast8_t cmd) {

pico/render.c

@@ -37,7 +37,7 @@ void render_loop() {
             break;
         default:
 #ifdef APPLE_MODEL_IIPLUS
-            if(videx_vterm_80col_enabled) {
+            if(videx_vterm_enabled && videx_vterm_80col_enabled) {
                 render_videx_text();
             } else
 #endif

pico/videx_vterm.c

@@ -7,6 +7,7 @@
 #include "vga.h"
 
 
+volatile bool videx_vterm_enabled;        // true -> the videx card is enabled
 volatile bool videx_vterm_80col_enabled;  // true -> the annunciator to enable 80-columns is on
 volatile bool videx_vterm_mem_selected;   // true -> videx memory is accessible at $C800-$CFFF
 volatile uint8_t videx_vram[2048];
@@ -40,8 +41,10 @@ static uint_fast32_t videx_cursor_mask = 0;
 static uint64_t videx_next_flash_tick = 0;
 
 
+// Initialize VideoTerm state
+//
+// Only called from the abus core
 void videx_vterm_init() {
-    // initializing registers
     videx_banknum = 0;
     videx_crtc_idx = 0;
     videx_crtc_regs[0] = 0x7b;
@@ -63,8 +66,29 @@ void videx_vterm_init() {
 }
 
 
+// Enable the VideoTerm support
+//
+// Only called from the abus core
+void videx_vterm_enable() {
+    videx_vterm_enabled = true;
+}
+
+
+// Disable the VideoTerm support
+//
+// Only called from the abus core
+void videx_vterm_disable() {
+    videx_vterm_enabled = false;
+}
+
+
 // Shadow accesses to card registers in $C0n0 - $C0nF range
+//
+// Only called from the abus core
 void videx_vterm_shadow_register(bool is_write, uint_fast16_t address, uint_fast8_t data) {
+    if(!videx_vterm_enabled)
+        return;
+
     // select the video memory bank
     videx_banknum = (address & 0x000c) >> 2;
 
@@ -84,7 +108,12 @@ void videx_vterm_shadow_register(bool is_write, uint_fast16_t address, uint_fast
 
 
 // Shadow bus accesses to the $C800-$CFFF memory space
+//
+// Only called from the abus core
 void videx_vterm_shadow_c8xx(bool is_write, uint_fast16_t address, uint_fast8_t value) {
+    if(!videx_vterm_enabled)
+        return;
+
     if(!videx_vterm_mem_selected)
         return;
 
@@ -104,6 +133,9 @@ void videx_vterm_shadow_c8xx(bool is_write, uint_fast16_t address, uint_fast8_t
 }
 
 
+// Update the internal VideoTerm flashing state
+//
+// Only called from the render core
 void videx_vterm_update_flasher() {
     uint64_t now = time_us_64();
     if(now > videx_next_flash_tick) {
@@ -196,6 +228,9 @@ static void render_videx_text_line(unsigned int line, uint text_base_addr, uint
 }
 
 
+// Render a screen of VideoTerm text mode
+//
+// Only called from the render core
 void render_videx_text() {
     vga_prepare_frame();
     // Skip 25 lines to center vertically

pico/videx_vterm.h

@@ -4,10 +4,13 @@
 #include <stdbool.h>
 
 
+extern volatile bool videx_vterm_enabled;
 extern volatile bool videx_vterm_80col_enabled;
 extern volatile bool videx_vterm_mem_selected;
 
 extern void videx_vterm_init();
+extern void videx_vterm_enable();
+extern void videx_vterm_disable();
 extern void videx_vterm_shadow_register(bool is_write, uint_fast16_t address, uint_fast8_t data);
 extern void videx_vterm_shadow_c8xx(bool is_write, uint_fast16_t address, uint_fast8_t value);