Posted on May 11, 2013 at 16:20 I noticed the CPAL
uses spin type
waits including at least one in an interrupt (see code below). Thes
e are u
sed
v
ia the MACRO
__CPAL_I2C_TIMEOUT
. I have some concern
with the one in the interrupt handl
er below because it appears to spin for 302 us = 20,536 cyles. The wait is on the B
TF flag which there is an interrupt for
(see table from STMf
4XX
reference manual.
Is there are reason
a spin wait
is done o
n the BTF rather than using the interrupt? I may want to optimize my code to recover the cyles. Were I to take a guess is would be that BTF is usu
ally not used in DMA transfers and is t
h
i
s not specially turned on in this case
.
For my cause it looks li
ke the wait occurs in the last two transmi
tted bytes
.
If sw
itching from DMA to interrupt mode saves 20
,
536
cycles on a single
write
I
may be
better off using
interrupt
mode.
Does ST have any opi
nion of th
e
relat
ive
efficiency
of Interrupt vs DMA in CPAL?
From cpal_i2c.c:
uint32_t
CPAL_I2C_DMA_TX_IRQHandler
(CPAL_InitTypeDef* pDevInitStruct)
{
/* Reinitialize Timeout Value to default (no timeout initiated) */
pDevInitStruct->wCPAL_Timeout = CPAL_I2C_TIMEOUT_DEFAULT;
CPAL_LOG(''\n\r\n\rLOG <CPAL_I2C_DMA_TX_IRQHandler> : I2C Device TX DMA '');
/*------------- If TC interrupt ------------*/
if((__CPAL_I2C_HAL_GET_DMATX_TCIT(pDevInitStruct->CPAL_Dev)) != 0)
{
CPAL_LOG(''\n\rLOG : I2C Device TX Complete'');
/* Update remaining number of data */
pDevInitStruct->pCPAL_TransferTx->wNumData = 0;
/* Call DMA TX TC UserCallback */
CPAL_I2C_DMATXTC_UserCallback(pDevInitStruct);
/* If DMA Normal mode */
if ((pDevInitStruct->wCPAL_Options & CPAL_OPT_DMATX_CIRCULAR) == 0)
{
/* If Master Mode selected */
if (pDevInitStruct->CPAL_Mode == CPAL_MODE_MASTER)
{
#ifdef CPAL_I2C_MASTER_MODE
/* Disable DMA Request */
__CPAL_I2C_HAL_DISABLE_DMAREQ(pDevInitStruct->CPAL_Dev);
/* Wait until BTF flag is set */
__CPAL_I2C_TIMEOUT(__CPAL_I2C_HAL_GET_BTF(pDevInitStruct->CPAL_Dev), CPAL_I2C_TIMEOUT_BTF);
/* No Stop Condition Generation option bit not selected */
if ((pDevInitStruct->wCPAL_Options & CPAL_OPT_I2C_NOSTOP) == 0)
John
