[ECOS] bugs on spi API
liang rainti
rainti_1212@hotmail.com
Tue Jul 26 10:26:00 GMT 2005
hi,all,
i am writing a qspi drivers on mcf5272 for eCos, the qspi has a
character:read and write in a transfer at one time. Referering generic SPI
API, cyg_spi_transfer( ) function can read spi device a transfer at one
time or write that. But read operation and write operation can not be
finished at the same time in the transfer( ) function.
eg.
A typical transaction might involve the following. First a command
should be sent to the device, consisting of four bytes. The device
will then respond with a single status byte, zero for failure,
non-zero for success. If successful then the device can accept another
n bytes of data, and will generate a 2-byte response including a
checksum. The device's chip select should remain asserted throughout.
The code for this would look something like:
#include <cyg/io/spi.h>
#include <cyg/hal/hal_io.h> // Defines the SPI devices
cyg_spi_transaction_begin(hal_spi_eprom);
// Interrupt-driven transfer, four bytes of command
!!! cyg_spi_transaction_transfer(hal_spi_eprom, 0, 4, command, NULL, 0);
// Read back the status
!!! cyg_spi_transaction_transfer(hal_spi_eprom, 0, 1, NULL, status, 0);
Why not be
cyg_spi_transaction_transfer(hal_spi_eprom,0,4,command,status,0)??? This
will be OK??? I am wondering.
if (!status[0]) {
// Command failed, generate some extra ticks to drop the chip
select
cyg_spi_transaction_tick(hal_spi_eprom, 0, 1);
} else {
// Transfer the data, then read back the final status. The
// chip select should be dropped at the end of this.
cyg_spi_transaction_transfer(hal_spi_eprom, 0, n, data, NULL, 0);
cyg_spi_transaction_transfer(hal_spi_eprom, 0, 2, NULL, status, 1);
// Code for checking the final status should go here
}
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