Cirrus-logic EP73xx Manual de usuario descargar pdf (Pagina 82)

7-2 EP7309/11/12 User’s Manual - DS508UM4

SDRAM Controller

Programming Example

;*****************************************************************************

; Sample initialization code for the SDRAM controller on the EDB7312:

;*****************************************************************************

;

ldr r0,=0x80000000 ; internal registers

ldr r3,=0x2000 ; local offset for memory

add r4,r3,r0 ; add & store offset in r4

mov r1,#0x522 ; CASLAT=2, SDSIZE=64 Mb, SDWIDTH=16, CLKCTL=0, SDACTIVE=1

str r1,[r4,#0x300] ; store in SDCONF

mov r1,#0x100 ; REFRATE=7.11 µS at 36 MHz BCLK

str r1,[r4,#0x340] ; store value in SDRFPR

;

Operational Overview

System Initialization

When the EP73xx encounters a power-on reset or a user reset, the SDRAM controller

is disabled. To configure the SDRAM controller:

1. Before initializing the controller, insure that the ENDP67 bit in the

SYSCON3 register is set to its default value of 0, and the DRAMZ bit in

SYSCON2 is set for the appropriate SDRAM access width.

2. Load the requested refresh rate into the SDRFPR register.

3. Write the SDCONF with a configuration word containing the desired

CASLAT, SDSIZE, SDWIDTH,and CLKCTL for your SDRAM devices plus

a 1 in the SDACTIVE bit field to activate the controller.

4. Cache (MMU) must be enabled for the SDRAM memory regions allocated

to the system software.

Immediately after initializing the controller, the SDRAM controller:

1. Sends a PRECHARGE command to all configured SDRAM banks.

2. Sends a LOAD MODE REGISTER command to all SDRAM devices in all

banks.

3. Loadsthe mode registers on all SDRAM devices with a configurationword

containing the CAS latency set in the CASLAT bits of SDCONF, a burst

length of 4, and the configuration bits to enable sequential programmed

length bursts.

4. Performs eight CBR (auto) refresh cycles to complete the initialization

sequence.

1 2 ... 77 78 79 80 81 82 83 84 85 86 87 ... 157 158

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Cirrus-logic EP73xx Manual de usuario Pagina 82