doc/README: documents and readme for NDS32 arch

Documents and READMEs for NDS32 architecture.
It patch also provides usage of SoC AG101 and board ADP-AG101.

Signed-off-by: Macpaul Lin <macpaul@andestech.com>

1 files changed, 21 insertions, 3 deletions

diff --git a/README b/README
index eb9ade9ad4..c6b179cb62 100644
--- a/README
+++ b/README
@@ -183,6 +183,10 @@ Directory Hierarchy:
       /mips32           Files specific to MIPS32 CPUs
       /xburst           Files specific to Ingenic XBurst CPUs
     /lib                Architecture specific library files
+  /nds32                Files generic to NDS32 architecture
+    /cpu                CPU specific files
+      /n1213            Files specific to Andes Technology N1213 CPUs
+    /lib                Architecture specific library files
   /nios2                Files generic to Altera NIOS2 architecture
     /cpu                CPU specific files
     /lib                Architecture specific library files
@@ -3156,7 +3160,7 @@ Low Level (hardware related) configuration options:
                 globally (CONFIG_CMD_MEM).
 
 - CONFIG_SKIP_LOWLEVEL_INIT
-                [ARM, MIPS only] If this variable is defined, then certain
+                [ARM, NDS32, MIPS only] If this variable is defined, then certain
                 low level initializations (like setting up the memory
                 controller) are omitted and/or U-Boot does not
                 relocate itself into RAM.
@@ -3723,8 +3727,8 @@ details; basically, the header defines the following image properties:
   Currently supported: Linux, NetBSD, VxWorks, QNX, RTEMS, LynxOS,
   INTEGRITY).
 * Target CPU Architecture (Provisions for Alpha, ARM, AVR32, Intel x86,
-  IA64, MIPS, Nios II, PowerPC, IBM S390, SuperH, Sparc, Sparc 64 Bit;
-  Currently supported: ARM, AVR32, Intel x86, MIPS, Nios II, PowerPC).
+  IA64, MIPS, NDS32, Nios II, PowerPC, IBM S390, SuperH, Sparc, Sparc 64 Bit;
+  Currently supported: ARM, AVR32, Intel x86, MIPS, NDS32, Nios II, PowerPC).
 * Compression Type (uncompressed, gzip, bzip2)
 * Load Address
 * Entry Point
@@ -4417,6 +4421,20 @@ On Nios II, the ABI is documented here:
     Note: on Nios II, we give "-G0" option to gcc and don't use gp
     to access small data sections, so gp is free.
 
+On NDS32, the following registers are used:
+
+        R0-R1:  argument/return
+        R2-R5:  argument
+        R15:    temporary register for assembler
+        R16:    trampoline register
+        R28:    frame pointer (FP)
+        R29:    global pointer (GP)
+        R30:    link register (LP)
+        R31:    stack pointer (SP)
+        PC:     program counter (PC)
+
+    ==> U-Boot will use R10 to hold a pointer to the global data
+
 NOTE: DECLARE_GLOBAL_DATA_PTR must be used with file-global scope,
 or current versions of GCC may "optimize" the code too much.