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* reading through i2c specs, little comment cleanup

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* add a few notes for future i2c bit-bangers
* cleanup of tracing
* no real functional change


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@42777 a95241bf-73f2-0310-859d-f6bbb57e9c96
This commit is contained in:
Alexander von Gluck IV 2011-09-29 15:03:49 +00:00
parent 17f2def171
commit 495a05fa9f
1 changed files with 30 additions and 23 deletions
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53
src/add-ons/accelerants/common/i2c.c
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@ -14,6 +14,7 @@
#include <OS.h> #include <OS.h>
#include <string.h> #include <string.h>
//#define TRACE_I2C //#define TRACE_I2C
#ifdef TRACE_I2C #ifdef TRACE_I2C
#ifdef __cplusplus #ifdef __cplusplus
@ -26,7 +27,11 @@ void _sPrintf(const char *format, ...);
#endif #endif
//! Timining for 100kHz bus (fractional parts are rounded up) /*!
I2c timings, rounded up (Phillips 1995 i2c bus specification, p20)
*/
//! Timing for standard mode i2c (100kHz max)
const static i2c_timing kTiming100k = { const static i2c_timing kTiming100k = {
.buf = 5, .buf = 5,
.hd_sta = 4, .hd_sta = 4,
@ -38,8 +43,8 @@ const static i2c_timing kTiming100k = {
.r = 2, .r = 2,
.f = 2, .f = 2,
.su_sto = 4, .su_sto = 4,
// as these are unspecified, we use half a clock cycle as a safe guess // these are unspecified, use half a clock cycle as a safe guess
.start_timeout = 5, .start_timeout = 5,
.byte_timeout = 5, .byte_timeout = 5,
.bit_timeout = 5, .bit_timeout = 5,
@ -47,8 +52,7 @@ const static i2c_timing kTiming100k = {
.ack_timeout = 5 .ack_timeout = 5
}; };
// timing for 400 kHz bus //! Timing for fast mode i2c (400kHz max)
// (argh! heavy up-rounding here)
const static i2c_timing kTiming400k = { const static i2c_timing kTiming400k = {
.buf = 2, .buf = 2,
.hd_sta = 1, .hd_sta = 1,
@ -60,8 +64,8 @@ const static i2c_timing kTiming400k = {
.r = 1, .r = 1,
.f = 1, .f = 1,
.su_sto = 1, .su_sto = 1,
// see kTiming100k // these are unspecified, use half a clock cycle as a safe guess
.start_timeout = 2, .start_timeout = 2,
.byte_timeout = 2, .byte_timeout = 2,
.bit_timeout = 2, .bit_timeout = 2,
@ -71,7 +75,7 @@ const static i2c_timing kTiming400k = {
/*! /*!
There's no spin in user space, but we need it to wait a couple There's no spin in user space, but we need it to wait a couple
of microseconds only of microseconds only
(in this case, snooze has much too much overhead) (in this case, snooze has much too much overhead)
*/ */
@ -121,7 +125,7 @@ send_start_condition(const i2c_bus *bus)
status = wait_for_clk(bus, bus->timing.start_timeout); status = wait_for_clk(bus, bus->timing.start_timeout);
if (status != B_OK) { if (status != B_OK) {
TRACE("send_start_condition(): Timeout sending start condition\n"); TRACE("%s: Timeout sending start condition\n", __func__);
return status; return status;
} }
@ -149,7 +153,7 @@ send_stop_condition(const i2c_bus *bus)
// to make the slave release bus control // to make the slave release bus control
status = wait_for_clk(bus, bus->timing.ack_timeout); status = wait_for_clk(bus, bus->timing.ack_timeout);
if (status != B_OK) { if (status != B_OK) {
TRACE("send_stop_condition(): Timeout sending stop condition\n"); TRACE("%s: Timeout sending stop condition\n", __func__);
return status; return status;
} }
@ -175,7 +179,7 @@ send_bit(const i2c_bus *bus, uint8 bit, int timeout)
status = wait_for_clk(bus, timeout); status = wait_for_clk(bus, timeout);
if (status != B_OK) { if (status != B_OK) {
TRACE("send_bit(): Timeout when sending next bit\n"); TRACE("%s: Timeout when sending next bit\n", __func__);
return status; return status;
} }
@ -201,7 +205,7 @@ send_acknowledge(const i2c_bus *bus)
status = wait_for_clk(bus, bus->timing.ack_start_timeout); status = wait_for_clk(bus, bus->timing.ack_start_timeout);
if (status != B_OK) { if (status != B_OK) {
TRACE("send_acknowledge(): Timeout when sending acknowledge\n"); TRACE("%s: Timeout when sending acknowledge\n", __func__);
return status; return status;
} }
@ -218,8 +222,8 @@ send_acknowledge(const i2c_bus *bus)
break; break;
if (system_time() - startTime > bus->timing.ack_timeout) { if (system_time() - startTime > bus->timing.ack_timeout) {
TRACE("send_acknowledge(): Slave didn't acknowledge byte within ack_timeout: %ld\n", TRACE("%s: slave didn't acknowledge byte within ack_timeout: %ld\n",
bus->timing.ack_timeout); __func__, bus->timing.ack_timeout);
return B_TIMEOUT; return B_TIMEOUT;
} }
@ -228,7 +232,7 @@ send_acknowledge(const i2c_bus *bus)
TRACE("send_acknowledge(): Success!\n"); TRACE("send_acknowledge(): Success!\n");
// make sure we've waited at least t_high // make sure we've waited at least t_high
spin(bus->timing.high); spin(bus->timing.high);
bus->set_signals(bus->cookie, 0, 1); bus->set_signals(bus->cookie, 0, 1);
@ -244,10 +248,10 @@ send_byte(const i2c_bus *bus, uint8 byte, bool acknowledge)
{ {
int i; int i;
//TRACE("send_byte(byte = %x)\n", byte); //TRACE("%s: (byte = %x)\n", __func__, byte);
for (i = 7; i >= 0; --i) { for (i = 7; i >= 0; --i) {
status_t status = send_bit(bus, byte >> i, status_t status = send_bit(bus, byte >> i,
i == 7 ? bus->timing.byte_timeout : bus->timing.bit_timeout); i == 7 ? bus->timing.byte_timeout : bus->timing.bit_timeout);
if (status != B_OK) if (status != B_OK)
return status; return status;
@ -266,6 +270,7 @@ send_slave_address(const i2c_bus *bus, int slaveAddress, bool isWrite)
{ {
status_t status; status_t status;
TRACE("%s: 0x%X\n", __func__, slaveAddress);
status = send_byte(bus, (slaveAddress & 0xfe) | !isWrite, true); status = send_byte(bus, (slaveAddress & 0xfe) | !isWrite, true);
if (status != B_OK) if (status != B_OK)
return status; return status;
@ -279,7 +284,7 @@ send_slave_address(const i2c_bus *bus, int slaveAddress, bool isWrite)
// - 0000 1xxx |-> reserved // - 0000 1xxx |-> reserved
// - 1111 1xxx | // - 1111 1xxx |
// - 1111 0xxx - 10 bit address (second byte contains remaining 8 bits) // - 1111 0xxx - 10 bit address (second byte contains remaining 8 bits)
// the lsb is 0 for write and 1 for read (except for general call address) // the lsb is 0 for write and 1 for read (except for general call address)
if ((slaveAddress & 0xff) != 0 && (slaveAddress & 0xf8) != 0xf0) if ((slaveAddress & 0xff) != 0 && (slaveAddress & 0xf8) != 0xf0)
return B_OK; return B_OK;
@ -302,7 +307,7 @@ receive_bit(const i2c_bus *bus, bool *bit, int timeout)
// wait for slave to raise clock // wait for slave to raise clock
status = wait_for_clk(bus, timeout); status = wait_for_clk(bus, timeout);
if (status != B_OK) { if (status != B_OK) {
TRACE("receive_bit(): Timeout waiting for bit sent by slave\n"); TRACE("%s: Timeout waiting for bit sent by slave\n", __func__);
return status; return status;
} }
@ -319,7 +324,7 @@ receive_bit(const i2c_bus *bus, bool *bit, int timeout)
// let it settle and leave it low for minimal time // let it settle and leave it low for minimal time
// to make sure slave has finished bit transmission too // to make sure slave has finished bit transmission too
*bit = data; *bit = data;
return B_OK; return B_OK;
} }
@ -360,7 +365,7 @@ receive_byte(const i2c_bus *bus, uint8 *resultByte, bool acknowledge)
static status_t static status_t
send_bytes(const i2c_bus *bus, const uint8 *writeBuffer, ssize_t writeLength) send_bytes(const i2c_bus *bus, const uint8 *writeBuffer, ssize_t writeLength)
{ {
TRACE("send_bytes(length = %ld)\n", writeLength); TRACE("%s: (length = %ld)\n", __func__, writeLength);
for (; writeLength > 0; --writeLength, ++writeBuffer) { for (; writeLength > 0; --writeLength, ++writeBuffer) {
status_t status = send_byte(bus, *writeBuffer, true); status_t status = send_byte(bus, *writeBuffer, true);
@ -376,7 +381,7 @@ send_bytes(const i2c_bus *bus, const uint8 *writeBuffer, ssize_t writeLength)
static status_t static status_t
receive_bytes(const i2c_bus *bus, uint8 *readBuffer, ssize_t readLength) receive_bytes(const i2c_bus *bus, uint8 *readBuffer, ssize_t readLength)
{ {
TRACE("receive_bytes(length = %ld)\n", readLength); TRACE("%s: (length = %ld)\n", __func__, readLength);
for (; readLength > 0; --readLength, ++readBuffer) { for (; readLength > 0; --readLength, ++readBuffer) {
status_t status = receive_byte(bus, readBuffer, readLength > 1); status_t status = receive_byte(bus, readBuffer, readLength > 1);
@ -423,7 +428,7 @@ i2c_send_receive(const i2c_bus *bus, int slaveAddress, const uint8 *writeBuffer,
return send_stop_condition(bus); return send_stop_condition(bus);
err: err:
TRACE("i2c_send_receive(): Cancelling transmission\n"); TRACE("%s: Cancelling transmission\n", __func__);
send_stop_condition(bus); send_stop_condition(bus);
return status; return status;
} }
@ -432,6 +437,7 @@ err:
void void
i2c_get100k_timing(i2c_timing *timing) i2c_get100k_timing(i2c_timing *timing)
{ {
// AKA standard i2c mode
memcpy(timing, &kTiming100k, sizeof(i2c_timing)); memcpy(timing, &kTiming100k, sizeof(i2c_timing));
} }
@ -439,5 +445,6 @@ i2c_get100k_timing(i2c_timing *timing)
void void
i2c_get400k_timing(i2c_timing *timing) i2c_get400k_timing(i2c_timing *timing)
{ {
// AKA fast i2c mode
memcpy(timing, &kTiming400k, sizeof(i2c_timing)); memcpy(timing, &kTiming400k, sizeof(i2c_timing));
} }