combined pchw and embedded into tiny. added section on arm to README

R=rsc
CC=golang-dev
https://golang.org/cl/194151

src/pkg/runtime/embedded/README

-small embedded target for arm
-define the c function write to make debug output work
-
-

src/pkg/runtime/embedded/mem.c

-// Copyright 2010 The Go Authors.  All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-#include "runtime.h"
-#include "malloc.h"
-
-// Assume there's an arbitrary amount of memory starting at "end".
-
-void*
-SysAlloc(uintptr ask)
-{
-	static byte *p;
-	extern byte end[];
-	byte *q;
-	
-	if(p == nil) {
-		p = end;
-		p += 7 & -(uintptr)p;
-	}
-	ask += 7 & -ask;
-
-	q = p;
-	p += ask;
-	·memclr(q, ask);
-	return q;
-}
-
-void
-SysFree(void *v, uintptr n)
-{
-	USED(v, n);
-}
-
-void
-SysUnused(void *v, uintptr n)
-{
-	USED(v, n);
-}
-

src/pkg/runtime/pchw/386/signal.c

-// nothing to see here

src/pkg/runtime/pchw/os.h

-// nothing to see here

src/pkg/runtime/pchw/thread.c

-// Copyright 2010 The Go Authors.  All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-#include "runtime.h"
-
-int8 *goos = "pchw";
-
-extern void ·write(int32 fd, void *v, int32 len, int32 cap);	// slice, spelled out
-
-int32
-write(int32 fd, void *v, int32 len)
-{
-	·write(fd, v, len, len);
-	return len;
-}
-
-void
-minit(void)
-{
-}
-
-void
-osinit(void)
-{
-}
-
-void
-initsig(void)
-{
-}
-
-void
-exit(int32)
-{
-	for(;;);
-}
-
-// single processor, no interrupts,
-// so no need for real concurrency or atomicity
-
-void
-newosproc(M *m, G *g, void *stk, void (*fn)(void))
-{
-	USED(m, g, stk, fn);
-	throw("newosproc");
-}
-
-void
-lock(Lock *l)
-{
-	if(m->locks < 0)
-		throw("lock count");
-	m->locks++;
-	if(l->key != 0)
-		throw("deadlock");
-	l->key = 1;
-}
-
-void
-unlock(Lock *l)
-{
-	m->locks--;
-	if(m->locks < 0)
-		throw("lock count");
-	if(l->key != 1)
-		throw("unlock of unlocked lock");
-	l->key = 0;
-}
-
-void
-noteclear(Note *n)
-{
-	n->lock.key = 0;
-}
-
-void
-notewakeup(Note *n)
-{
-	n->lock.key = 1;
-}
-
-void
-notesleep(Note *n)
-{
-	if(n->lock.key != 1)
-		throw("notesleep");
-}
-

src/pkg/runtime/tiny/386/signal.c

+// just the write function
+
+extern void ·write(int32 fd, void *v, int32 len, int32 cap);	// slice, spelled out
+
+int32
+write(int32 fd, void *v, int32 len)
+{
+	·write(fd, v, len, len);
+	return len;
+}

src/pkg/runtime/pchw/README → src/pkg/runtime/tiny/README

 This directory contains a simple example of how one might
-start Go running on bare hardware.  It is very primitive but
-can run go/test/sieve.go, the concurrent prime sieve, on a
-uniprocessor.  It has only been tested using the Bochs emulator.
+start Go running on bare hardware. There is currently code
+for 386 and arm.
+
+
+386
+
+It is very primitive but can run go/test/sieve.go, the concurrent
+prime sieve, on a uniprocessor.  It has only been tested using the
+Bochs emulator.
 
 To run, first build the tools by running all.bash with GOARCH=386
 and GOOS set to your normal GOOS (linux, darwin).  Then:
 
-	export GOOS=pchw
+	export GOOS=tiny
 	cd $GOROOT/src/pkg/runtime
 	make clean
 	make install
-	cd pchw
+	cd tiny
 	8g $GOROOT/test/sieve.go
 	8l sieve.8
 	8l -a sieve.8 >sieve.asm	# can consult sieve.asm for debugging
@@ -22,8 +28,43 @@ You may have to tweak the .bochsrc depending on your system,
 and you may need to install the Bochs emulator.
 
 
+ARM
+
+First build the toolchain using GOARCH=arm and GOOS=linux. When
+you build your embedded code set GOARCH=tiny.
+
+	export GOOS=tiny
+	cd $GOROOT/src/pkg/runtime
+	make clean
+	make install
+
+On arm the tiny runtime doesn't define a low level write function. You can either
+define a stub if you don't need debug output, or more usefully, define it to
+print to some debug serial port. Here is a sample function that prints to
+the DBGU on an at91sam7s:
+
+#define DBGU_CSR  ((uint32*)   0xFFFFF214) // (DBGU) Channel Status Register
+#define US_TXRDY        ((uint32) 0x1 <<  1) // (DBGU) TXRDY Interrupt
+#define DBGU_THR  ((uint32*)   0xFFFFF21C) // (DBGU) Transmitter Holding Register
+
+int32
+write(int32 fd, void* b, int32 n)
+{
+	uint32 i;
+	uint8* s = (uint8*)b;
+
+	for (i = 0; i < n; i++) {
+		while ((*DBGU_CSR & US_TXRDY) == 0) {
+		}
+		*DBGU_THR = *s;
+		s++;
+	}
+	return n;
+}
+
+
 
-The bootblock is from MIT's xv6 project and carries this notice:
+The 386 bootblock is from MIT's xv6 project and carries this notice:
 
     The xv6 software is:
     

src/pkg/runtime/embedded/thread.c → src/pkg/runtime/tiny/thread.c

@@ -4,7 +4,7 @@
 
 #include "runtime.h"
 
-int8 *goos = "embedded";
+int8 *goos = "tiny";
 
 void
 minit(void)