Why does xdata memory work incorrectly in MK?

Question

Microcontrollers

AD89C51RD2 microcontroller, 64 KB on-board memory, 1792 B XRAM. There is a firmware for it with several thousand lines, here are its dimensions: "Program Size: data=76.5 xdata=820 code=38246". The problem occurs precisely with the xdata memory area.
The program has variables that I write to this memory area like:

float         xdata ppk2K72 = 0.9843;
float         xdata ppk2K73 = 0.99698;
float         xdata ppk2K61 = 0.99596;
float         xdata ppk2K62 = 0.99849;

There are more than 100 such variables and they must be stored in memory.
So while these variables were commented out and did not clog memory, the program worked correctly, but as soon as it came time to use them, I reflashed my device, then there were obvious glitches associated with memory overflow. The program displays chaotic characters from memory, overwrites some other variables with incorrect values ​​... The glitch disappears when I free the XDATA memory area, which I have set to the maximum amount of memory:

void initialization()
{
EA =     1; 		// enable interrupts
CKRL =   0xFF;      //Clock Reload Register for calculating core frequency
CKCON0 = 0x01;      // X2 mode for all peripherals
CKCON1 = 0x00;      // X2 for SPI
AUXR |= 0x10;       // XDATA = 1792
IPH0 = 0x00;        // низкий уровень прерываний для всей переферии
IPL0 = 0x00;
//********** UART Mode 1 (8 bit) with int_BRD
PCON |=   0x80;     // SMOD1 = 1
SCON =    0x50;		// uart in mode 1 (8 bit), REN=1
BDRCON &= ~0xEC;     // BRR=0; SRC=0;
BDRCON |= 0x0E;		// TBCK=1;RBCK=1; SPD=1 
BRL =     0xB8;		// 9600 Bds at 11.092MHz 
ES =      1; 	    // Enable serial interrupt
BDRCON |= 0x10;     // Baud rate generator run           

TI = 0;
RI = 0;
}

Answer 1

I can’t say anything, I can advise the forum
electronix.ru/forum/index.php?showforum=74

Answer 2

where is your stack? does not intersect with xdata?

Answer 3

Here is the startup file generated by KEY

$NOMOD51
;------------------------------------------------------------------------------
;  This file is part of the C51 Compiler package
;  Copyright (c) 1988-2005 Keil Elektronik GmbH and Keil Software, Inc.
;  Version 8.01
;
;  *** <<< Use Configuration Wizard in Context Menu >>> ***
;------------------------------------------------------------------------------
;  STARTUP.A51:  This code is executed after processor reset.
;
;  To translate this file use A51 with the following invocation:
;
;     A51 STARTUP.A51
;
;  To link the modified STARTUP.OBJ file to your application use the following
;  Lx51 invocation:
;
;     Lx51 your object file list, STARTUP.OBJ  controls
;
;------------------------------------------------------------------------------
;
;  User-defined <h> Power-On Initialization of Memory
;
;  With the following EQU statements the initialization of memory
;  at processor reset can be defined:
;
; <o> IDATALEN: IDATA memory size <0x0-0x100>
;     <i> Note: The absolute start-address of IDATA memory is always 0
;     <i>       The IDATA space overlaps physically the DATA and BIT areas.
IDATALEN        EQU     80H
;
; <o> XDATASTART: XDATA memory start address <0x0-0xFFFF> 
;     <i> The absolute start address of XDATA memory
XDATASTART      EQU     0     
;
; <o> XDATALEN: XDATA memory size <0x0-0xFFFF> 
;     <i> The length of XDATA memory in bytes.
XDATALEN        EQU     0      
;
; <o> PDATASTART: PDATA memory start address <0x0-0xFFFF> 
;     <i> The absolute start address of PDATA memory
PDATASTART      EQU     0H
;
; <o> PDATALEN: PDATA memory size <0x0-0xFF> 
;     <i> The length of PDATA memory in bytes.
PDATALEN        EQU     0H
;
;</h>
;------------------------------------------------------------------------------
;
;<h> Reentrant Stack Initialization
;
;  The following EQU statements define the stack pointer for reentrant
;  functions and initialized it:
;
; <h> Stack Space for reentrant functions in the SMALL model.
;  <q> IBPSTACK: Enable SMALL model reentrant stack
;     <i> Stack space for reentrant functions in the SMALL model.
IBPSTACK        EQU     0       ; set to 1 if small reentrant is used.
;  <o> IBPSTACKTOP: End address of SMALL model stack <0x0-0xFF>
;     <i> Set the top of the stack to the highest location.
IBPSTACKTOP     EQU     0xFF +1     ; default 0FFH+1  
; </h>
;
; <h> Stack Space for reentrant functions in the LARGE model.      
;  <q> XBPSTACK: Enable LARGE model reentrant stack
;     <i> Stack space for reentrant functions in the LARGE model.
XBPSTACK        EQU     0       ; set to 1 if large reentrant is used.
;  <o> XBPSTACKTOP: End address of LARGE model stack <0x0-0xFFFF>
;     <i> Set the top of the stack to the highest location.
XBPSTACKTOP     EQU     0xFFFF +1   ; default 0FFFFH+1 
; </h>
;
; <h> Stack Space for reentrant functions in the COMPACT model.    
;  <q> PBPSTACK: Enable COMPACT model reentrant stack
;     <i> Stack space for reentrant functions in the COMPACT model.
PBPSTACK        EQU     0       ; set to 1 if compact reentrant is used.
;
;   <o> PBPSTACKTOP: End address of COMPACT model stack <0x0-0xFFFF>
;     <i> Set the top of the stack to the highest location.
PBPSTACKTOP     EQU     0xFF +1     ; default 0FFH+1  
; </h>
;</h>
;------------------------------------------------------------------------------
;
;  Memory Page for Using the Compact Model with 64 KByte xdata RAM
;  <e>Compact Model Page Definition
;
;  <i>Define the XDATA page used for PDATA variables. 
;  <i>PPAGE must conform with the PPAGE set in the linker invocation.
;
; Enable pdata memory page initalization
PPAGEENABLE     EQU     0       ; set to 1 if pdata object are used.
;
; <o> PPAGE number <0x0-0xFF> 
; <i> uppermost 256-byte address of the page used for PDATA variables.
PPAGE           EQU     0
;
; <o> SFR address which supplies uppermost address byte <0x0-0xFF> 
; <i> most 8051 variants use P2 as uppermost address byte
PPAGE_SFR       DATA    0A0H
;
; </e>
;------------------------------------------------------------------------------

; Standard SFR Symbols 
ACC     DATA    0E0H
B       DATA    0F0H
SP      DATA    81H
DPL     DATA    82H
DPH     DATA    83H

                NAME    ?C_STARTUP


?C_C51STARTUP   SEGMENT   CODE
?STACK          SEGMENT   IDATA

                RSEG    ?STACK
                DS      1

                EXTRN CODE (?C_START)
                PUBLIC  ?C_STARTUP

                CSEG    AT      0
?C_STARTUP:     LJMP    STARTUP1

                RSEG    ?C_C51STARTUP

STARTUP1:

IF IDATALEN <> 0
                MOV     R0,#IDATALEN - 1
                CLR     A
IDATALOOP:      MOV     @R0,A
                DJNZ    R0,IDATALOOP
ENDIF

IF XDATALEN <> 0
                MOV     DPTR,#XDATASTART
                MOV     R7,#LOW (XDATALEN)
  IF (LOW (XDATALEN)) <> 0
                MOV     R6,#(HIGH (XDATALEN)) +1
  ELSE
                MOV     R6,#HIGH (XDATALEN)
  ENDIF
                CLR     A
XDATALOOP:      MOVX    @DPTR,A
                INC     DPTR
                DJNZ    R7,XDATALOOP
                DJNZ    R6,XDATALOOP
ENDIF

IF PPAGEENABLE <> 0
                MOV     PPAGE_SFR,#PPAGE
ENDIF

IF PDATALEN <> 0
                MOV     R0,#LOW (PDATASTART)
                MOV     R7,#LOW (PDATALEN)
                CLR     A
PDATALOOP:      MOVX    @R0,A
                INC     R0
                DJNZ    R7,PDATALOOP
ENDIF

IF IBPSTACK <> 0
EXTRN DATA (?C_IBP)

                MOV     ?C_IBP,#LOW IBPSTACKTOP
ENDIF

IF XBPSTACK <> 0
EXTRN DATA (?C_XBP)

                MOV     ?C_XBP,#HIGH XBPSTACKTOP
                MOV     ?C_XBP+1,#LOW XBPSTACKTOP
ENDIF

IF PBPSTACK <> 0
EXTRN DATA (?C_PBP)
                MOV     ?C_PBP,#LOW PBPSTACKTOP
ENDIF

                MOV     SP,#?STACK-1

; This code is required if you use L51_BANK.A51 with Banking Mode 4
;<h> Code Banking
; <q> Select Bank 0 for L51_BANK.A51 Mode 4
#if 0   
;     <i> Initialize bank mechanism to code bank 0 when using L51_BANK.A51 with Banking Mode 4.
EXTRN CODE (?B_SWITCH0)
                CALL    ?B_SWITCH0      ; init bank mechanism to code bank 0
#endif
;</h>
                LJMP    ?C_START

                END