AM335x GPMC Timing Optimal Settings

Guilherme Costa

Hello,

I'm working with a custom am335x board, using kernel version 3.6.12, a MT29F1G08ABBDAH4-IT:D NAND memory, and JFFS2 partitions, and I'm currently trying to optimize the memory throughput.

Currently, this is my average write speed:

root@AM335x:/mnt/extra# dd if=/dev/urandom of=test bs=256k count=40
40+0 records in
40+0 records out
10485760 bytes (10.0MB) copied, 14.042668 seconds, 729.2KB/s

I had a worse results before, but I messed around with the GPMC timing settings and managed to improve them to the current level. :)

This is my current gpmc_timing configuration (values are in nanoseconds and GPMC_FCLK is 100MHz):

static struct gpmc_timings am335x_nand_timings = {
   .sync_clk = 0,

   .cs_on = 0,
   .cs_rd_off = 20,
   .cs_wr_off = 20,

   .adv_on = 0,
   .adv_rd_off = 20,
   .adv_wr_off = 20,
   .we_off = 10,     
   .oe_off = 10,     

   .access = 20,
   .rd_cycle = 20,
   .wr_cycle = 20,

   .wr_access = 20,
   .wr_data_mux_bus = 0,
};

I know that the GPMC timing configuration depends on a set of rules that must be followed, and that multiple configurations may work (with better or worse performances). So, this is my question: is there a guide showing how to obtain the optimal configuration values?

Regards,

Guilherme

over 9 years ago

0 Titusrathinaraj Stalin over 9 years ago

TI__Guru** 116100 points

Please refer to the following TI wikis.
processors.wiki.ti.com/.../StarterWare_GPMC
processors.wiki.ti.com/.../Tips_for_configuring_OMAP35x,_AM35x,_and_AM-DM37x_GPMC_registers
processors.wiki.ti.com/.../Linux_Core_NAND_User's_Guide

0 Guilherme Costa over 9 years ago in reply to Titusrathinaraj Stalin

Intellectual 635 points

Titus,

I've followed the guides you posted, as well as checked out the TRM for the AM335x and Micron's manual for my memory model. I've arrived at the following configurations:

static struct gpmc_timings am335x_nand_timings = {                              
   .sync_clk = 0,                                                               
                                                                                
   .cs_on = 0,                                                                  
   .cs_rd_off = 40,                                                             
   .cs_wr_off = 30,                                                             
                                                                                
   .adv_on = 0,                                                                 
   .adv_rd_off = 40,                                                            
   .adv_wr_off = 30,                                                            
   .we_off = 10,                                                                
   .oe_off = 20,                                                                
                                                                                
   .access = 20,                                                                
   .rd_cycle = 40,                                                              
   .wr_cycle = 30,                                                              
                                                                                
   //Not used on AM335x                                                   
   .wr_access = 0,                                                              
   .wr_data_mux_bus = 0,                                                        
};

With these, my board boots just fine. However, it is my understanding that I should try to set my timing equal to, or greater than the minimum recommended by the manufacturer. This is where things get tricky: the manual says that the minimum WE# pulse width is 12ns when Vcc = 1.8V (p. 77), which, I believe, is controlled by setting we_off. However, my board only boots if we_off = 10. I've looked everywhere in the manuals trying to find some limitation to we_off based on the other values, but had no luck.

What am I missing? Is my interpretation correct?

Regards,

Guilherme

0 Guilherme Costa over 9 years ago in reply to Guilherme Costa

Intellectual 635 points

Found out what the problem was. I had misunderstood the meaning of the we_off configuration in the memory datasheet. It should be around 10ns (as it is configured), not 12ns.

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AM335x GPMC Timing Optimal Settings