# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1541259737 -3600
# Node ID 51cbfbb4c17e00d139836f07d39cd24fb9c9c792
# Parent  254ee12221e275699dd9252be7b494bc13b4c7f3
Maintain separate addresses for updating the display, permitting access to
off-screen framebuffers.

diff -r 254ee12221e2 -r 51cbfbb4c17e examples/vga/main.c
--- a/examples/vga/main.c	Sat Nov 03 14:05:05 2018 +0100
+++ b/examples/vga/main.c	Sat Nov 03 16:42:17 2018 +0100
@@ -163,6 +163,9 @@
                              sprite_width, sprite_height,
                              x, y, 0x8c, 1);
 
+                /* Update the display with the frame details. */
+
+                vga_set_frame(&display_config);
                 wait(delay);
 
                 /* Copy to the display from the store, restoring the original
diff -r 254ee12221e2 -r 51cbfbb4c17e include/vga_display.h
--- a/include/vga_display.h	Sat Nov 03 14:05:05 2018 +0100
+++ b/include/vga_display.h	Sat Nov 03 16:42:17 2018 +0100
@@ -50,9 +50,13 @@
 
     uint32_t line;
 
-    /* Pointers to pixel lines. */
+    /* Screen start address, frame limit, current pixel line. */
+
+    uint8_t *screen_start, *screen_limit, *linedata;
 
-    uint8_t *linedata;
+    /* Screen size, used to wrap the current line pointer. */
+
+    uint32_t screen_size;
 
     /* General display configuration. */
 
@@ -84,6 +88,10 @@
 void vga_configure_zero_channel(int channel, int int_num, int initiating,
                                 uint32_t output);
 
+/* Frame selection. */
+
+void vga_set_frame(display_config_t *display_config);
+
 /* Interrupt handlers. */
 
 void vga_interrupt_handler(void);
diff -r 254ee12221e2 -r 51cbfbb4c17e lib/vga_display.c
--- a/lib/vga_display.c	Sat Nov 03 14:05:05 2018 +0100
+++ b/lib/vga_display.c	Sat Nov 03 16:42:17 2018 +0100
@@ -58,6 +58,10 @@
        Otherwise, transfers are initiated by the line timer. */
 
     vga_display.transfer_int_num = transfer_int_num;
+
+    /* Update the addresses used for the display. */
+
+    vga_set_frame(display_config);
 }
 
 /* Initialise a separate transfer timer if different from the general display
@@ -243,6 +247,17 @@
 
 
 
+/* Update the display addresses from the general display configuration. */
+
+void vga_set_frame(display_config_t *display_config)
+{
+    vga_display.screen_start = display_config->screen_start;
+    vga_display.screen_limit = display_config->screen_limit;
+    vga_display.screen_size = display_config->screen_size;
+}
+
+
+
 /* Display state machine interrupt handler. */
 
 void vga_interrupt_handler(void)
@@ -325,7 +340,7 @@
 
     /* Set the line address. */
 
-    vga_display.linedata = vga_display.display_config->screen_start;
+    vga_display.linedata = vga_display.screen_start;
 
     if (vga_display.line_channels)
         start_visible();
@@ -345,8 +360,8 @@
         {
             vga_display.linedata += cfg->line_length;
 
-            if (vga_display.linedata >= cfg->screen_limit)
-                vga_display.linedata -= cfg->screen_size;
+            if (vga_display.linedata >= vga_display.screen_limit)
+                vga_display.linedata -= vga_display.screen_size;
         }
 
         if (vga_display.line_channels)