From fdf44365e56c3741f47cbd421a57f0d074a5492c Mon Sep 17 00:00:00 2001
From: Miquel Sabaté Solà <mikisabate@gmail.com>
Date: Thu, 23 Jan 2025 16:14:12 +0100
Subject: fx: Provide an example of PPU bank switching
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Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
---
 shared/mmc3.s | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100644 shared/mmc3.s

(limited to 'shared/mmc3.s')

diff --git a/shared/mmc3.s b/shared/mmc3.s
new file mode 100644
index 0000000..b3f484a
--- /dev/null
+++ b/shared/mmc3.s
@@ -0,0 +1,23 @@
+;;; Useful macros and constants for development on the MMC3 chip.
+
+.scope MMC3
+    BANK_SELECT = $8000
+    BANK_DATA   = $8001
+    MIRRORING   = $A000
+    RAM_PROTECT = $A001
+    IRQ_LATCH   = $C000
+    IRQ_RELOAD  = $C001
+    IRQ_DISABLE = $E000
+    IRQ_ENABLE  = $E001
+.endscope
+
+.macro BANK_REGISTER_SET REGISTER_ID, REGISTER_VALUE
+    .if REGISTER_ID < 0 || REGISTER_ID > 7
+        .error "bad value for REGISTER_ID when bank switching"
+    .endif
+
+    lda #REGISTER_ID
+    sta MMC3::BANK_SELECT
+    lda #REGISTER_VALUE
+    sta MMC3::BANK_DATA
+.endmacro
-- 
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