91 lines
2.5 KiB
C
91 lines
2.5 KiB
C
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/*
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* eeprom-24c01.c — Velxio custom chip implementing a 24C01-class I2C EEPROM.
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*
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* 128 bytes (datasheet says 1 Kbit = 128 × 8). Address pins A0..A2 set the
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* three low bits of the 7-bit I2C address (base 0x50).
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*
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* Protocol on the I2C bus:
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* write 1 byte → set the read/write address pointer
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* write 2+ bytes → first sets address pointer, rest stores data sequentially
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* read → returns memory at pointer, autoincrements
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*
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* Build:
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* bash scripts/compile-chip.sh sdk/examples/eeprom-24c01.c fixtures/eeprom-24c01.wasm
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*/
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#include "velxio-chip.h"
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#include <stdlib.h>
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#include <string.h>
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#define EEPROM_BASE_ADDR 0x50
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#define EEPROM_SIZE 128
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typedef enum {
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ST_IDLE, /* before any byte after addressing */
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ST_HAS_POINTER, /* received the pointer byte; further writes are data */
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} ee_state;
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typedef struct {
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vx_pin a0, a1, a2;
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uint8_t pointer;
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uint8_t mem[EEPROM_SIZE];
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ee_state state;
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} chip_state_t;
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static bool i2c_connect(void* ud, uint8_t address, bool is_read) {
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chip_state_t* s = (chip_state_t*)ud;
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/* On a fresh transaction, reads use the existing pointer; writes restart. */
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if (!is_read) s->state = ST_IDLE;
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return true; /* ACK */
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}
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static uint8_t i2c_read(void* ud) {
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chip_state_t* s = (chip_state_t*)ud;
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uint8_t b = s->mem[s->pointer & (EEPROM_SIZE - 1)];
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s->pointer = (s->pointer + 1) & (EEPROM_SIZE - 1);
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return b;
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}
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static bool i2c_write(void* ud, uint8_t byte) {
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chip_state_t* s = (chip_state_t*)ud;
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if (s->state == ST_IDLE) {
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s->pointer = byte & (EEPROM_SIZE - 1);
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s->state = ST_HAS_POINTER;
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} else {
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s->mem[s->pointer & (EEPROM_SIZE - 1)] = byte;
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s->pointer = (s->pointer + 1) & (EEPROM_SIZE - 1);
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}
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return true; /* ACK */
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}
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static void i2c_stop(void* ud) {
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chip_state_t* s = (chip_state_t*)ud;
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s->state = ST_IDLE;
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}
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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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uint8_t addr = EEPROM_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 = i2c_connect,
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.on_read = i2c_read,
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.on_write = i2c_write,
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.on_stop = i2c_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("24C01 EEPROM ready");
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}
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