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LPC11C24: Proper CAN timings

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This commit is contained in:
Pavel Kirienko
2015-08-24 15:43:16 +03:00
parent b334dbbfe5
commit 03ed261477
2 changed files with 28 additions and 27 deletions
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libuavcan_drivers/lpc11c24/driver/include/uavcan_lpc11c24/can.hpp
+1 -1
View File
@@ -33,7 +33,7 @@ public:
* Returns negative value if the requested baudrate can't be used.
* Returns zero if OK.
*/
int init(uavcan::uint32_t baudrate);
int init(uavcan::uint32_t bitrate);
bool hasReadyRx() const;
bool hasEmptyTx() const;
libuavcan_drivers/lpc11c24/driver/src/can.cpp
+27 -26
View File
@@ -121,40 +121,41 @@ public:
RxQueue rx_queue;
int computeBaudrate(std::uint32_t baud_rate, std::uint32_t can_api_timing_cfg[2])
struct BitTimingSettings
{
const std::uint32_t pclk = Chip_Clock_GetMainClockRate();
const std::uint32_t clk_per_bit = pclk / baud_rate;
for (std::uint32_t div = 0; div <= 15; div++)
std::uint32_t canclkdiv;
std::uint32_t canbtr;
bool isValid() const { return canbtr != 0; }
};
/**
* http://www.bittiming.can-wiki.info
*/
BitTimingSettings computeBitTimings(std::uint32_t bitrate)
{
if (Chip_Clock_GetSystemClockRate() == 48000000) // 48 MHz is optimal for CAN timings
{
for (std::uint32_t quanta = 1; quanta <= 32; quanta++)
switch (bitrate)
{
for (std::uint32_t segs = 3; segs <= 17; segs++)
{
if (clk_per_bit == (segs * quanta * (div + 1)))
{
segs -= 3;
const std::uint32_t seg1 = segs / 2;
const std::uint32_t seg2 = segs - seg1;
const std::uint32_t can_sjw = (seg1 > 3) ? 3 : seg1;
can_api_timing_cfg[0] = div;
can_api_timing_cfg[1] = ((quanta - 1) & 0x3F) |
(can_sjw & 0x03) << 6 |
(seg1 & 0x0F) << 8 |
(seg2 & 0x07) << 12;
return 0;
}
}
case 1000000: return BitTimingSettings{ 0, 0x0505 }; // 8 quanta, 87.5%
case 500000: return BitTimingSettings{ 0, 0x1c05 }; // 16 quanta, 87.5%
case 250000: return BitTimingSettings{ 0, 0x1c0b }; // 16 quanta, 87.5%
case 125000: return BitTimingSettings{ 0, 0x1c17 }; // 16 quanta, 87.5%
default: return BitTimingSettings{ 0, 0 };
}
}
return -1;
else
{
return BitTimingSettings{ 0, 0 };
}
}
} // namespace
CanDriver CanDriver::self;
int CanDriver::init(uavcan::uint32_t baudrate)
int CanDriver::init(uavcan::uint32_t bitrate)
{
CriticalSectionLocker locker;
@@ -167,12 +168,12 @@ int CanDriver::init(uavcan::uint32_t baudrate)
* C_CAN init
*/
Chip_Clock_EnablePeriphClock(SYSCTL_CLOCK_CAN);
static std::uint32_t can_api_init_table[2];
if (computeBaudrate(baudrate, can_api_init_table) != 0)
auto bit_timings = computeBitTimings(bitrate);
if (!bit_timings.isValid())
{
return -1;
}
LPC_CCAN_API->init_can(can_api_init_table, true);
LPC_CCAN_API->init_can(reinterpret_cast<std::uint32_t*>(&bit_timings), true);
static CCAN_CALLBACKS_T ccan_callbacks =
{
canRxCallback,