It is required to call pid_ioctl function when you set or use SPI. Available commands of pid_ioctl function for SPI are as follows:
|set||lsb||0||set a bit transmission order: MSB first|
|1||set a bit transmission order: LSB first|
|data||8||set a size of data unit: 8 bits|
|16||set a size of data unit: 16 bits|
|div||[N]||set a division: 2/4/8/16/32/64/128/256|
|mode||[M]||set an SPI mode: 0/1/2/3|
|nss||id||N||select a SPI slave, 0 ~ 7|
|dev||uio0||#pin||assign a uio pin as a Slave Select(SS) pin|
|get||rxlen||get the number of pending bytes in receive buffer|
|txlen||get the number of pending bytes in send buffer|
|txfree||get the free send buffer size|
|req||start||request to write data|
|reset||request to reset bus|
You can set SPI mode, bit transmission order, size of data unit and division by using a "set" command.
You can set 0 or 1 for setting SPI bit transmission order and the default value is 0. If this value is set to 0, MSB will be transmitted first. How to set the bit transmission order is as follows:
|Bit Transmission Order||Syntax|
|MSB > LSB||pid_ioctl($pid, "set lsb 0");|
|LSB > MSB||pid_ioctl($pid, "set lsb 1");|
You can set 8 or 16 for setting size of data unit and the default value is 8. How to set the size of data unit is as follows:
|Size of Data Unit||Syntax|
|8 bits||pid_ioctl($pid, "set data 8");|
|16 bits||pid_ioctl($pid, "set data 16");|
Data rate depends on division rate of PHPoC's basic clock and you can choose one of the division rate values of 2 / 4 / 8 / 16 / 32 / 64 / 128 / 256. The default value is 256. How to set the data rate is as follows:
|1 of N||pid_ioctl($pid, "set div N");|
※ Basic clock of P4S-341/P4S-342 is 42MHz. Thus, data rate is approximately 164Kbps when the division rate is set to 256.
You can set one of SPI modes of 0 to 3 and the default value is 3. How to set SPI mode is as follows:
|mode 0||pid_ioctl($pid, "set mode 0");|
|mode 1||pid_ioctl($pid, "set mode 1");|
|mode 2||pid_ioctl($pid, "set mode 2");|
|mode 3||pid_ioctl($pid, "set mode 3");|
When the PHPoC communicates with more than one slave, you can select a slave using the "set nss id" command. PHPoC can communicate with up to 8 SPI slaves. ID can be selected from 0 ~ 7 and the default is 0.
|Select N th slave||pid_ioctl($pid, "set nss N");|
The each slave select(SS) pin of the slave which has an ID 1 to 7 can be set using the "set nss dev" command. A uio device name and a pin number should be specified after this command.
pid_ioctl($pid, "set nss id 1");
pid_ioctl($pid, "set nss dev uio0 4");
pid_ioctl($pid, "set nss id 2");
pid_ioctl($pid, "set nss dev uio0 5");
***※ Note: Slave select pin (SS) of slave ID 0 is fixed to 0th pin of uio0 and can not be changed to another pin.
You can get status of SPI by using "get" command.
How to get the number of pending bytes in receive and send buffer as follows:
|Send buffer||pid_ioctl($pid, "get txlen");|
|Receive buffer||pid_ioctl($pid, "get rxlen");|
How to get the remaining size of send buffer in byte-unit is as follows:
|remaining size of send buffer||pid_ioctl($pid, "get txfree");|
You can request to write data with this command. You should input data to send buffer before using this command. After writing data, you should read data from an SPI slave as much as you sent. How to use this command is as follows:
|Request to Write Data||pid_ioctl($pid, "req start");|
You can reset an SPI bus with this command when communication is bad.
|Request to Request Bus||pid_ioctl($pid, "req reset");|