86 lines
2.6 KiB
C
86 lines
2.6 KiB
C
/*
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* pcf8574.c — 8-bit I2C I/O expander.
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*
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* Pins: A0, A1, A2 (address bits, base 0x20), SDA, SCL, INT (open-drain interrupt),
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* P0..P7 (quasi-bidirectional I/O lines).
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*
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* Protocol: master writes 1 byte → drives Px outputs to that pattern.
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* master reads 1 byte → returns the current state of Px lines.
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* (Real PCF8574 quasi-bidirectional behavior simplified: outputs latch the
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* master's writes; reads expose the latched value or external drivers.)
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*/
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#include "velxio-chip.h"
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#include <stdlib.h>
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#define PCF_BASE_ADDR 0x20
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static const char* P_NAMES[8] = {"P0","P1","P2","P3","P4","P5","P6","P7"};
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typedef struct {
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vx_pin A0, A1, A2, INT;
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vx_pin P[8];
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uint8_t latched; /* last value written by the master */
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} chip_state_t;
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static bool on_connect(void* ud, uint8_t addr, bool is_read) { return true; }
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static void update_outputs(chip_state_t* s) {
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for (int i = 0; i < 8; i++) {
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vx_pin_write(s->P[i], (s->latched >> i) & 1 ? VX_HIGH : VX_LOW);
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}
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}
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static bool on_write(void* ud, uint8_t byte) {
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chip_state_t* s = (chip_state_t*)ud;
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s->latched = byte;
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update_outputs(s);
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return true;
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}
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static uint8_t on_read(void* ud) {
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chip_state_t* s = (chip_state_t*)ud;
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/* Reading returns the line state — for outputs we drove, that's `latched`;
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* for inputs (pin read by host), we'd read each pin. Simplification: return
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* the pin reads OR the latch as the current state of each line. */
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uint8_t val = 0;
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for (int i = 0; i < 8; i++) {
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if (vx_pin_read(s->P[i])) val |= (uint8_t)(1 << i);
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}
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return val;
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}
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static void on_stop(void* ud) { /* no-op */ }
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void chip_setup(void) {
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chip_state_t* s = (chip_state_t*)calloc(1, sizeof(chip_state_t));
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s->A0 = vx_pin_register("A0", VX_INPUT);
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s->A1 = vx_pin_register("A1", VX_INPUT);
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s->A2 = vx_pin_register("A2", VX_INPUT);
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s->INT = vx_pin_register("INT", VX_OUTPUT_HIGH); /* open-drain, idle HIGH */
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for (int i = 0; i < 8; i++) {
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s->P[i] = vx_pin_register(P_NAMES[i], VX_OUTPUT_HIGH);
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}
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s->latched = 0xff; /* power-on default per datasheet */
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update_outputs(s);
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uint8_t addr = PCF_BASE_ADDR
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| ((vx_pin_read(s->A2) & 1) << 2)
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| ((vx_pin_read(s->A1) & 1) << 1)
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| ((vx_pin_read(s->A0) & 1));
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vx_i2c_config cfg = {
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.address = addr,
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.scl = vx_pin_register("SCL", VX_INPUT),
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.sda = vx_pin_register("SDA", VX_INPUT),
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.on_connect = on_connect,
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.on_read = on_read,
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.on_write = on_write,
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.on_stop = on_stop,
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.user_data = s,
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};
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vx_i2c_attach(&cfg);
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vx_log("PCF8574 I/O expander ready");
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}
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