Hi Kuo-Jung,
On Fri, 2013-11-29 at 08:59 +0800, Kuo-Jung Su wrote:
No it's a common misunderstanding, I also made the same mistake before. Please check my bug fix for Faraday FTI2C010 I2C driver:
http://patchwork.ozlabs.org/patch/294732/
The address should be rebuild inside the i2c driver in u-boot's I2C model.
Another example could be found at drivers/i2c/soft_i2c.c, line 382 - 389
static int soft_i2c_read (...) { ...... shift = (alen-1) * 8; while(alen-- > 0) { if(write_byte(addr >> shift)) { PRINTD("i2c_read, address not <ACK>ed\n"); return(1); } shift -= 8; } ...... }
However the root cause is the u-boot i2c driver model, the address should never be passed to i2c_read/i2c_write in uint format.
Please take a peak at how ecos defineds the relative i2c routines:
externC cyg_uint32 cyg_i2c_transaction_tx(const cyg_i2c_device*, cyg_bool, const cyg_uint8*, cyg_uint32, cyg_bool); externC cyg_uint32 cyg_i2c_transaction_rx(const cyg_i2c_device*, cyg_bool, cyg_uint8*, cyg_uint32, cyg_bool, cyg_bool);
In this way, the eeprom address would be forced to rebuild in address pointer (i.e., addr[]) as what we did in SPI mode.
Unfortunately I still cannot agree with you. In my opinion I2C driver has nothing to do with current situation.
It's purely how manufacturers of EEPROM use I2C. For example I we use "PCF8594C-2" EEPROM. Here's a datasheet - http://www.nxp.com/documents/data_sheet/PCF8594C_2.pdf
Its capacity is 512 bytes. And as you may see from "Fig 3. Device addressing." Each IC houses 2 virtual EEPROMs (each housing 256 bytes of data).
And if you accept this philosophy you'll understand why "I2C chip address" is modified and why following approach is used in "cmd_eeprom.c" for "CONFIG_SYS_I2C_EEPROM_ADDR_LEN == 1" (which says that EEPROM has address length of 1 byte): ================== addr[0] = offset >> 8; /* block number */ addr[1] = blk_off; /* block offset */ addr[0] |= dev_addr; /* insert device address */ ==================
From source code above you see that virtually it addresses multiple 256
byte EEPROMs.
Regards, Alexey