From 7dbdf1ee0a064e9b2c5fedd7bd4e2b67f0532b09 Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <kwojtus@protonmail.com>
Date: Tue, 17 Dec 2019 17:01:41 +0100
Subject: make things work again on real hw (setting system mode moved to
 boot.S)

---
 psr.h | 55 -------------------------------------------------------
 1 file changed, 55 deletions(-)

(limited to 'psr.h')

diff --git a/psr.h b/psr.h
index dfbb878..9809fc4 100644
--- a/psr.h
+++ b/psr.h
@@ -64,59 +64,4 @@ inline static PSR_t read_CPSR(void)
   return CPSR;
 }
 
-//// Write function not working for some reason... Assembly from gcc
-//// looks ok. Needs checking on real hw.
-
-//inline static void write_CPSR(PSR_t CPSR)
-//{
-  // write to current program status register and synchronize context
-  //  asm("msr cpsr, %0\n\r"
-  //      "isb" :: "r" (CPSR.raw) : "memory");
-//}
-
-inline static void set_system_mode(void)
-{
-  // hack to fix an unexplained bug; volatile needed in case of
-  // compilation with optimizations
-  volatile PSR_t CPSR __attribute__((unused)) = read_CPSR();
-
-  //// there are 2 ways of changing mode, both with the same
-  //// problem (see the long comment below)
-
-  //// way 1
-  // CPSR.fields.M_4_0 = MODE_SYSTEM;
-  // write to current program status register and synchronize context
-  // asm("msr cpsr, %0\n\r"
-  //     "isb":: "r" (CPSR.raw) : "memory");  
-
-  //// way 2
-  asm("cps #0b11111\n\r"
-      "isb" ::: "memory");
-}
-
-// The thing with writing to cpsr is weird. I used to have a single
-// function that would set the system mode by:
-//   1. reading the cpsr
-//   2. modifying the value using bit shifts and logical or
-//   3. writing the value back
-// When introducing structs and bitfields I wanted to have separate
-// functions for reading and writing the cpsr and have code up the
-// call stack handle value modification. For some reason this didn't
-// work - all would just hang when writing the CPSR. It turned out
-// everything works if i call read_CPSR() from the same function, in
-// which i write to cpsr. And I don't even need to use the value
-// I read. I can just discard it (we're compiling without
-// optimizations, so read_CPSR() is still called) and use the value
-// passed as argument. I noticed an even weirder thing: the 2nd way
-// of changing mode (cps instruction) doesn't work normally, but,
-// just as msr, it does work when I call read_CPSR() before it. Even
-// weirder - I cannot replace read_CPSR() with the actual assembly it
-// does, because it stops working again! Asm generated by gcc looks
-// ok, so Idk, maybe its some qemu issue (haven't tested on real RPi
-// yet). I seem to have experienced uart printing inserted here and
-// there do the same magic read_CPSR() does (but, again, not always).
-// Unfortunately, nop repeated several hundreds times (or a recursive
-// nop function, that just calls itself a given number of times)
-// doesn't have this magical property :(
-
 #endif // PSR_H
-- 
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