from richard miller:

Revised advice message for firmware version compatibility (rev numbering 
was dropped around Jul 2013 and resumed as a timestamp on 19 Aug).

Reference: /n/atom/patch/applied2013/bcm-fw-date
Date: Fri Sep 20 14:42:18 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/9/bcm/main.c	Fri Sep 20 14:41:59 2013
+++ /sys/src/9/bcm/main.c	Fri Sep 20 14:41:59 2013
@@ -10,9 +10,14 @@
 
 #include "reboot.h"
 
+enum {
+	/* space for syscall args, return PC, top-of-stack struct */
+	Ustkheadroom	= sizeof(Sargs) + sizeof(uintptr) + sizeof(Tos),
+};
+
 /* Firmware compatibility */
 #define	Minfirmrev	326770
-#define	Minfirmdate	"22 Jul 2012"
+#define	Minfirmdate	"19 Aug 2013"
 
 /*
  * Where configuration info is left for the loaded programme.
@@ -266,9 +271,10 @@
 	rev = getfirmware();
 	print("firmware: rev %d\n", rev);
 	if(rev < Minfirmrev){
-		print("Sorry, firmware (start.elf) must be at least rev %d (%s)\n",
-			Minfirmrev, Minfirmdate);
-		for(;;){}
+		print("Sorry, firmware (start*.elf) must be at least rev %d"
+		      " or newer than %s\n", Minfirmrev, Minfirmdate);
+		for(;;)
+			;
 	}
 	trapinit();
 	clockinit();
@@ -349,7 +355,7 @@
 	 * of the argument list checked in syscall.
 	 */
 	i = oargblen+1;
-	p = UINT2PTR(STACKALIGN(base + BY2PG - sizeof(Tos) - i));
+	p = UINT2PTR(STACKALIGN(base + BY2PG - Ustkheadroom - i));
 	memmove(p, oargb, i);
 
 	/*
@@ -441,7 +447,7 @@
 	uintptr pa;
 	char *p;
 
-	if((p = getconf("*maxmem")) != nil) {
+	if((p = getconf("*maxmem")) != nil){
 		memsize = strtoul(p, 0, 0) - PHYSDRAM;
 		if (memsize < 16*MB)		/* sanity */
 			memsize = 16*MB;