From ecb1db7159975775150472a5f3d737759decd123 Mon Sep 17 00:00:00 2001
From: Alan Cox <alan@linux.intel.com>
Date: Tue, 25 Oct 2016 21:47:09 +0100
Subject: [PATCH] pdp11: initial low level bits (incomplete)

---
 Kernel/lowlevel-pdp11.S | 91 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)
 create mode 100644 Kernel/lowlevel-pdp11.S

diff --git a/Kernel/lowlevel-pdp11.S b/Kernel/lowlevel-pdp11.S
new file mode 100644
index 00000000..38491f38
--- /dev/null
+++ b/Kernel/lowlevel-pdp11.S
@@ -0,0 +1,91 @@
+#include "kernel-pdp11.def"
+
+	.globl _di
+	.globl _ei
+	.globl _irqrestore
+	.globl _doexec
+	.globl ___udivhi3
+	.globl ___umodhi3
+	.globl _abort
+	.globl outr0hex
+	.globl outstring
+
+/*	Probably should go to ipl6 not ipl7 to allow profiling ?
+
+	This is slightly odd compared with most machines. Rather than
+	having special move to/from control register instructions the
+	status register actually lives at the very top of the unibus device
+	address space - for now 077776 and the other control registers work
+	in a very similar way */
+
+_di:
+	mov 0177776,r0
+	bis 0340,0177776
+	rts pc
+_ei:
+	mov 0177776,r0
+	bic 0340,0177776
+	rts pc
+_irqrestore:
+	mov 2(sp),0177776
+	rts pc
+
+
+/*	FIXME: need correct code for MMU supervisor/user case */
+
+_doexec:
+#if CONFIG_PDP11_04
+	mov 2(sp),r0			/* Jump address */
+	mov $_udata+U_DATA__U_ISP,sp	/* user stack = kernel for simple */
+	clr -(sp)
+	move r0,-(sp)
+	clr r0
+	clr r1
+	clr r2
+	clr r3
+	clr r4
+	clr r5
+	rtt
+#else
+	mov 2(sp),r0
+	mov $_udata+U_DATA__U_ISP,r1
+	mov r1,0177717		/* user mode stack pointer */
+	mov $_udata+512,sp	/* rewind to the top of kernel stack */
+
+	/* PSW is
+	   [mode.2][prevmode.2][grs][revid.2][cissusp][pri.3][flags]
+	   00: kernel 01: supervisor, 11 user*/
+
+	/* Make a trap frame */
+	mov $0xC000,-(sp)	/* user, was kernel */
+	mov r0,-(sp)
+	clr r0			/* no leaks */
+	clr r1
+	clr r2
+	clr r3
+	clr r4
+	clr r5
+	rtt			/* IRQ on, user space return */
+#endif
+	
+
+___udivhi3:
+___umodhi3:
+_abort:
+	rts pc
+
+outr0hex:
+	rts pc
+
+outstring:
+	mov r1,-(sp)
+	mov r0,r1
+1:
+	movb (r1)+,r0
+	tstb r0
+	beq 2f
+	jsr pc,outchar
+	jmp 1
+2:
+	mov (sp)+,r1
+	rts pc
-- 
2.34.1