From 80584d7aac412fb739b661fc59666c7fa6baf90e Mon Sep 17 00:00:00 2001
From: Abe Kabakoff <occamsshavingkit@gmail.com>
Date: Sat, 18 Jul 2026 17:50:08 +0200
Subject: [PATCH] fix: initialize SPI callback union member for SPI-mode builds
 (AUD-003)
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The WIZCHIP global initializer at wizchip_conf.c:256-277 only initialized
the IF.BUS union member (iodata_t (*)(uint32_t) signatures), even when
_WIZCHIP_IO_MODE_ selected SPI mode. W5500 SPI access calls through
IF.SPI._read_byte (uint8_t (*)(void)) and IF.SPI._write_byte
(void (*)(uint8_t)) — incompatible signatures through the wrong union
member, which can HardFault or corrupt memory on common ARM ABIs.

Fix: when _WIZCHIP_IO_MODE_ has the SPI bit set, initialize IF.SPI
with the existing wizchip_spi_readbyte/wizchip_spi_writebyte stubs
(return 0 / no-op) and NULL burst callbacks. BUS mode keeps its
existing initialization under #else.
---
 Ethernet/wizchip_conf.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/Ethernet/wizchip_conf.c b/Ethernet/wizchip_conf.c
index 9409b60..7eb7253 100644
--- a/Ethernet/wizchip_conf.c
+++ b/Ethernet/wizchip_conf.c
@@ -264,6 +264,16 @@ _WIZCHIP  WIZCHIP = {
         wizchip_cs_select,
         wizchip_cs_deselect
     },
+#if (_WIZCHIP_IO_MODE_ & _WIZCHIP_IO_MODE_SPI_)
+    {
+        .SPI = {
+            ._read_byte   = wizchip_spi_readbyte,
+            ._write_byte  = wizchip_spi_writebyte,
+            ._read_burst  = 0,
+            ._write_burst = 0
+        }
+    }
+#else
     {
         {
             //M20150601 : Rename the function
@@ -274,6 +284,7 @@ _WIZCHIP  WIZCHIP = {
         },
 
     }
+#endif
 };