Hi,
I am using transfer() function in spidev_test.c to verify the data
throughput on phytec LPC3250 board.
2KBytes SPI message is sent out to SPI Slave device.
There is a big delay (80us or so) after every 11 words transmission (
20 us or so, which is reasonable at 8MHz SPI Clock).
==== I am wondering where is this significant delay coming from??? ======
It largely reduced the SPI data througput.
It does not look like 'Linux Kernel Context switch'.
See attached Timing Info on Scope. (TimingOnScope.txt)
SPI board setting is as follows (8MHZ spi clock, 16bit data size,
interrupt transfer)
static struct pl022_config_chip spi1_chip_info = {
.lbm = LOOPBACK_DISABLED,
.com_mode = INTERRUPT_TRANSFER,
.iface = SSP_INTERFACE_MOTOROLA_SPI,
.hierarchy = SSP_MASTER,
.slave_tx_disable = 0,
.endian_tx = SSP_TX_LSB,
.endian_rx = SSP_RX_LSB,
.data_size = SSP_DATA_BITS_16, //SSP_DATA_BITS_8,
.rx_lev_trig = SSP_RX_4_OR_MORE_ELEM,
.tx_lev_trig = SSP_TX_4_OR_MORE_EMPTY_LOC,
.clk_phase = SSP_CLK_FIRST_EDGE, //SSP_CLK_SECOND_EDGE,
.clk_pol = SSP_CLK_POL_IDLE_LOW,
.ctrl_len = SSP_BITS_8,
.wait_state = SSP_MWIRE_WAIT_ZERO,
.duplex = SSP_MICROWIRE_CHANNEL_FULL_DUPLEX,
.cs_control = phy3250_spi1_cs_set,
};
Kernel (2.6.34) is using default 100ms context switch. ' CONFIG_HZ=100. '
Any help is appreciated.
Regards,
Quentin
|<--20us 11words-->|<-- 80us delay -->|<-- Next 11 words....
_ _ _ _ _ _
| | | | ... | | | | ..... | | | | ...............
___| |_| |_ _| |_| |_________ _______| |_| |_
------------------------------------------------------------------------------
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