ref: dc0f1ae1028206a548cc5fad15631d79c212e48a
dir: /sys/src/9/bcm/i2cgpio.c/
/* * I²C bitbang driver using GPIO pins. */ #include "u.h" #include "../port/lib.h" #include "../port/error.h" #include "mem.h" #include "dat.h" #include "fns.h" #include "io.h" #include "../port/i2c.h" typedef struct Ctlr Ctlr; struct Ctlr { uint sda, scl; int delay; }; static void Setpin(uint pin, int val) { gpiosel(pin, val?Input:Output); gpioout(pin, val); } static int Getpin(uint pin) { return gpioin(pin); } static void Delay(Ctlr *ctlr) { microdelay(ctlr->delay); } static int Stretch(Ctlr *ctlr) { ulong to; to = µs(); do { if(Getpin(ctlr->scl)) return 0; } while(µs() - to < 25*1000); return -1; } static int Writebit(Ctlr *ctlr, int bit) { Setpin(ctlr->sda, bit); Delay(ctlr); Setpin(ctlr->scl, 1); Delay(ctlr); if(Stretch(ctlr) < 0) return -1; if(bit && !Getpin(ctlr->sda)) return -2; Setpin(ctlr->scl, 0); return 0; } static int Readbit(Ctlr *ctlr) { int bit; Setpin(ctlr->sda, 1); Delay(ctlr); Setpin(ctlr->scl, 1); if(Stretch(ctlr) < 0) return -1; Delay(ctlr); bit = Getpin(ctlr->sda); Setpin(ctlr->scl, 0); return bit; } static int Readbyte(Ctlr *ctlr, int nack) { int byte, i, e; byte = 0; for(i=0; i<8; i++){ if((e = Readbit(ctlr)) < 0) return e; byte <<= 1; byte |= e; } if((e = Writebit(ctlr, nack)) < 0) return e; return byte; } static int Writebyte(Ctlr *ctlr, int byte) { int i, e; for(i=0; i<8; i++){ if((e = Writebit(ctlr, (byte>>7)&1)) < 0) return e; byte <<= 1; } return Readbit(ctlr); } static int Start(Ctlr *ctlr) { if(!Getpin(ctlr->sda) || !Getpin(ctlr->scl)) return -2; Setpin(ctlr->sda, 0); Delay(ctlr); Setpin(ctlr->scl, 0); return 0; } static int Restart(Ctlr *ctlr) { Setpin(ctlr->sda, 1); Delay(ctlr); Setpin(ctlr->scl, 1); if(Stretch(ctlr) < 0) return -1; Delay(ctlr); return Start(ctlr); } static int Stop(Ctlr *ctlr) { Setpin(ctlr->sda, 0); Delay(ctlr); Setpin(ctlr->scl, 1); if(Stretch(ctlr) < 0){ Setpin(ctlr->sda, 1); return -1; } Delay(ctlr); Setpin(ctlr->sda, 1); Delay(ctlr); return 0; } static int init(I2Cbus *bus) { Ctlr *ctlr = bus->ctlr; ctlr->delay = 1 + (1000000 / (2 * bus->speed)); Setpin(ctlr->sda, 1); Setpin(ctlr->scl, 1); gpiopullup(ctlr->sda); gpiopullup(ctlr->scl); return 0; } static int io(I2Cdev *dev, uchar *pkt, int olen, int ilen) { I2Cbus *bus = dev->bus; Ctlr *ctlr = bus->ctlr; int i, o, v, alen; alen = olen > 0; if(olen > alen && (pkt[0] & 0xF8) == 0xF0) alen++; if((v = Start(ctlr)) < 0) return -1; if(olen > alen) pkt[0] &= ~1; for(o=0; o<olen; o++){ if((v = Writebyte(ctlr, pkt[o])) != 0) goto Stop; } if(ilen <= 0 || olen <= 0) goto Stop; if((pkt[0]&1) == 0){ if((v = Restart(ctlr)) < 0) goto Stop; pkt[0] |= 1; for(i=0; i<alen; i++){ if((v = Writebyte(ctlr, pkt[i])) != 0) goto Stop; } } for(i=1; i<=ilen; i++){ if((v = Readbyte(ctlr, i==ilen)) < 0) goto Stop; pkt[o++] = v; } Stop: if(v == -2) /* arbitration lost */ return -1; Stop(ctlr); return o; } void i2cgpiolink(void) { static Ctlr ctlr1 = { .sda = 2, .scl = 3, }; static I2Cbus i2c1 = {"i2c1", 100*1000, &ctlr1, init, io}; addi2cbus(&i2c1); }