Analyzing NOR Flash Timing (S3C2440)

The timing of the programmable access cycle of the S3C2440 memory controller is:

The time parameters (Tacc, Tacs, Tcoh, etc.) in the above figure are all programmable.

Let's take a look at the timing of NOR Flash:

All we need to do is set the timing of the S3C2440 Nor Flash controller (BANK0 of the memory controller) to meet the timing of the Nor Flash chip.

The reference range of each parameter can be obtained through the AC CHARACTERISTICS of Nor Flash.

Combining the two pictures of the Nor Flash chip, we can get the following information:

After sending the address data (Addresses), you need to wait for Taa (required to be greater than or equal to 70ns) time for the address data to be valid;

After sending the chip select signal (CE#), you need to wait for Tce (required to be greater than or equal to 70ns) time before the chip select signal is valid;

After sending the read signal (OE#), you need to wait for the Toe time (required to be greater than or equal to 30ns) for the read signal to be valid;

For simplicity, we send out the address data (Addresses), chip select signal (CE#), and read signal (OE#) at the same time, and then let them all wait for 70ns (wait for the signal to be valid). Corresponding to the read timing diagram of the Nor Flash controller of S3C2440, the address signal A[24:0], chip select signal nGCS, and read signal nOE need to be sent out at the same time, and keep Tacc greater than or equal to 70ns.

According to the reference manual of S3C2240, Nor Flash is connected to BANKCON0, so we only need to set BANKCON0.

The default value of Tacc is 14 clocks. When the system is powered on, a 12MHz crystal oscillator is used. HCLK=12MHz, Tacc=(1000/12*14)≈1166ns. This value is very large and can almost meet all Nor Flash requirements.

After startup, set HCLK to 100MHz, T=1000/100=10ns, Tacc needs to be greater than or equal to 70ns, so set Tacc equal to 101, 8 clocks.

#include "s3c2440_soc.h"

void bank0_tacc_set(int val)

{

BANKCON0 = val << 8;

}