Hello all.
This is proving to be more complicated than it seemed (or I am more clumsy than I thought).
I think I've made some progress, but basically I'm still at the same point.
On the one hand, I've found [1] a keyboard driver among the qmk ones, which does something very similar to what I'm trying to do; it controls the rows from the pins of a promicro and reads the column values from three shift-registers (SN74HC165). It reads the shift-registers via SPI, as I want to do. The code in matrix.c is quite simple, almost to copy it directly.
On the other hand, following this advice:
MMcM wrote: ↑13 Nov 2022, 23:54
It might be profitable to google around for some Arduino code that talks to one of these devices via SPI. The SPI routines are similar enough that you can probably crib off it.
I found a page where it explains how to control a MCP23S08 like the one I have, from arduino [2].
Now for the bad news. Although everything seems to be well configured, I still don't have a correct reading of the MCP23S08 values. The code I have now is the following:
Code: Select all
void matrix_init_custom(void) {
// init SPI
spi_init();
spi_start(SPI_MATRIX_CHIP_SELECT_PIN, false, 0, SPI_MATRIX_DIVISOR);
setPinOutput(SPI_MATRIX_CHIP_SELECT_PIN);
writePinHigh(SPI_MATRIX_CHIP_SELECT_PIN);
}
bool matrix_scan_custom(matrix_row_t current_matrix[]) {
bool changed = false;
static matrix_row_t current_row_value = 0;
// Read from SPI the matrix
writePinLow(SPI_MATRIX_CHIP_SELECT_PIN);
wait_ms(20); // delay needed (?)
//matrix_output_select_delay();
writePinHigh(SPI_MATRIX_CHIP_SELECT_PIN);
spi_status_t read_result = spi_read();
if (read_result >= 0) {
/* only if SPI read successful: populate the matrix row with the
state of the 8 consecutive column bits */
uprintf("read_result = %i\n",(uint8_t)read_result);
}
return changed;
}
Whether the pins have signal or not, it always reads the same values; 0 or 127, with some values in between (120,64,96) if I pass a high enough value to wait_ms() (20ms seems correct.). Also, I've noticed that if I don't include a slight delay, it always reads 0. But as I said, it's independent of whether the GPx pins have a signal or not.
MMcM wrote: ↑13 Nov 2022, 23:54
You should look at the return value from spi_receive. If I am not mistaken, the only time this device will send you anything is
when you write a register that you want to read.
I think the next thing to do is write some subroutines to read and write the MCP registers. You can do that without the MCP being connected to the matrix at all. If you pick a read/write one, like the pull-up register, you can verify that you read back what you wrote. Then you can proceed to configure them for the actual scan.
And another thing that has surprised me is that, with the spi functions of qmk (spi_master.h), it is not clear how to select which io expander to read from in case of having several in series, nor how to control the registers... It may also be something above my level.
Thanks in advance
[1]
https://github.com/qmk/qmk_firmware/tre ... d/dqz11n1g
[2]
https://www.instructables.com/MCP23S08-With-Arduino/