ipodvideo: detect ram size at boot (doesn't actually get USED yet)

This is the first step to allowing a single build which will work on any ipodvideo.

A global variable, probed_ramsize, is initialised to either 32 or 64 early in boot.


git-svn-id: svn://svn.rockbox.org/rockbox/trunk@27937 a1c6a512-1295-4272-9138-f99709370657

firmware/target/arm/crt0-pp.S

@@ -137,6 +137,24 @@ pad_skip:
     mov    r1, #0
     str    r1, [r2]
 
+#if defined(IPOD_VIDEO)
+    /* detect 32mb vs 64mb model */
+    /* we do this here because after SDRAM is remapped, we already assumed */
+    /* its size to be whatever we were compiled for. */
+
+    mov    r2, #0x12000000
+    mov    r3, #64
+    strb   r3, [r2, #-1]   /* first write 64 to last byte of first 32MB bank */
+
+    mov    r2, #0x14000000
+    mov    r3, #32
+    strb   r3, [r2, #-1]   /* now write 32 to last byte of second 32MB bank */
+
+    /* now the last word of the first 32MB bank tells you the RAM size */
+    /* since on a 32MB model both writes will touch the same actual location */
+    /* this is read later on in boot */
+#endif
+
     mov    r2, #0x40000000
     ldr    r3, =remap_start
     ldr    r4, =remap_end

firmware/target/arm/system-pp502x.c

@@ -42,6 +42,10 @@ extern void SERIAL0(void);
 static struct corelock cpufreq_cl SHAREDBSS_ATTR;
 #endif
 
+#if defined(IPOD_VIDEO) && !defined(BOOTLOADER)
+unsigned char probed_ramsize;
+#endif
+
 void __attribute__((interrupt("IRQ"))) irq_handler(void)
 {
     if(CURRENT_CORE == CPU)
@@ -518,6 +522,13 @@ void system_init(void)
 #else
         pp_set_cpu_frequency(CPUFREQ_MAX);
 #endif
+
+#if defined(IPOD_VIDEO)
+        /* crt0-pp.S wrote the ram size to the last byte of the first 32MB
+           ram bank. See the comment there for how we determine it. */
+        volatile unsigned char *end32 = (volatile unsigned char *)0x01ffffff;
+        probed_ramsize = *end32;
+#endif
     }
 
     init_cache();

firmware/target/arm/system-target.h

@@ -172,6 +172,10 @@ static inline void wake_core(int core)
 #define HAVE_CPUCACHE_FLUSH
 #endif
 
+#if defined(IPOD_VIDEO) && !defined(BOOTLOADER)
+extern unsigned char probed_ramsize;
+#endif
+
 #endif /* CPU_PP */
 
 #endif /* SYSTEM_TARGET_H */