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-rw-r--r--stm-fmc.c107
1 files changed, 50 insertions, 57 deletions
diff --git a/stm-fmc.c b/stm-fmc.c
index 698f7af..01e642c 100644
--- a/stm-fmc.c
+++ b/stm-fmc.c
@@ -39,8 +39,6 @@
static SRAM_HandleTypeDef _fmc_fpga_inst;
static HAL_StatusTypeDef _fmc_init_params(void);
-static int _fmc_nwait_idle(void);
-
HAL_StatusTypeDef fmc_init(void)
{
@@ -59,83 +57,78 @@ HAL_StatusTypeDef fmc_init(void)
}
+static int _fmc_nwait_idle(void)
+{
+ int cnt;
+
+ // poll NWAIT (number of iterations is limited)
+ for (cnt=0; cnt<FMC_FPGA_NWAIT_MAX_POLL_TICKS; cnt++)
+ {
+ // read pin state
+ if (HAL_GPIO_ReadPin(FMC_GPIO_PORT_NWAIT, FMC_GPIO_PIN_NWAIT) == FMC_NWAIT_IDLE)
+ return 0;
+ }
+
+ return -1;
+}
+
int fmc_write_32(uint32_t addr, uint32_t *data)
{
// calculate target fpga address
uint32_t ptr = FMC_FPGA_BASE_ADDR + (addr & FMC_FPGA_ADDR_MASK);
- // write data to fpga
- HAL_StatusTypeDef ok = HAL_SRAM_Write_32b(&_fmc_fpga_inst, (uint32_t *)ptr, data, 1);
+ int status =
+ // write data to fpga
+ (HAL_SRAM_Write_32b(&_fmc_fpga_inst, (uint32_t *)ptr, data, 1) != HAL_OK) ||
+ // wait for transaction to complete
+ _fmc_nwait_idle();
- // check for error
- if (ok != HAL_OK) return -1;
-
- // wait for transaction to complete
- int wait = _fmc_nwait_idle();
+ return status;
+}
- // check for timeout
- if (wait != 0) return -1;
+static inline int _fmc_read_32(uint32_t *ptr, uint32_t *data)
+{
+ return
+ // read data from fpga
+ (HAL_SRAM_Read_32b(&_fmc_fpga_inst, (uint32_t *)ptr, data, 1) != HAL_OK) ||
+ // wait for transaction to complete
+ _fmc_nwait_idle();
- // everything went ok
- return 0;
}
-
int fmc_read_32(uint32_t addr, uint32_t *data)
{
// calculate target fpga address
uint32_t ptr = FMC_FPGA_BASE_ADDR + (addr & FMC_FPGA_ADDR_MASK);
- // perform dummy read transaction
- HAL_StatusTypeDef ok = HAL_SRAM_Read_32b(&_fmc_fpga_inst, (uint32_t *)ptr, data, 1);
-
- // check for error
- if (ok != HAL_OK) return -1;
-
- // wait for dummy transaction to complete
- int wait = _fmc_nwait_idle();
-
- // check for timeout
- if (wait != 0) return -1;
-
- // read data from fpga
- ok = HAL_SRAM_Read_32b(&_fmc_fpga_inst, (uint32_t *)ptr, data, 1);
+ /* Pavel says:
+ * The short story is like, on one hand STM32 has a dedicated FMC_NWAIT
+ * pin, that can be used in variable-latency data transfer mode. On the
+ * other hand STM32 also has a very nasty hardware bug associated with
+ * FMC_WAIT, that causes processor to freeze under certain conditions.
+ * Because of this FMC_NWAIT cannot be used and FPGA can't properly signal
+ * to STM32, when data transfer is done. Because of that we have to read
+ * two times.
+ */
- // check for error
- if (ok != HAL_OK) return -1;
+ /* Add some level of reentrancy protection. When running under a
+ * preemptive multitasker, with two threads banging on the fpga, we appear
+ * to sometimes read the wrong value. I think this is because the second
+ * read counts on the first read to put the correct value on the address
+ * bus.
+ */
+ __disable_irq();
- // wait for read transaction to complete
- wait = _fmc_nwait_idle();
+ int status =
+ _fmc_read_32((uint32_t *)ptr, data) ||
+ _fmc_read_32((uint32_t *)ptr, data);
- // check for timeout
- if (wait != 0) return -1;
+ __enable_irq();
- // everything went ok
- return 0;
+ return status;
}
-static int _fmc_nwait_idle()
-{
- int cnt; // counter
-
- // poll NWAIT (number of iterations is limited)
- for (cnt=0; cnt<FMC_FPGA_NWAIT_MAX_POLL_TICKS; cnt++)
- {
- // read pin state
- GPIO_PinState nwait = HAL_GPIO_ReadPin(FMC_GPIO_PORT_NWAIT, FMC_GPIO_PIN_NWAIT);
-
- // stop waiting if fpga is ready
- if (nwait == FMC_NWAIT_IDLE) break;
- }
-
- // check for timeout
- if (cnt >= FMC_FPGA_NWAIT_MAX_POLL_TICKS) return -1;
-
- // ok
- return 0;
-}
-
void fmc_init_gpio(void)
{
GPIO_InitTypeDef GPIO_InitStruct;