I am wanting to increase the length of one of my characteristics used when my device is acting as a peripheral. When I increase the size of my characteristic, the softdevice requires a large amount of extra RAM (more RAM than I can spare) but if I remove one 2 byte field from this characteristic then the softdevice requires no extra RAM. Why is this?
Key points about my device:
- s332 v5.0
- NRF52832
- SDK v14.2.
- 8 central connections
- 5 peripheral connections
- The characteristic in question supports notifications and reads
- hvn_tx_queue_size is set to 30
My original structure is
typedef struct{ uint8_t gps_state; /**< GPS State */ uint8_t num_satellites; /**< Number of GNSS satellites */ uint16_t gps_accuracy; /**< Accuracy in (m)*/} ble_gps_t;
My original scatter file is
; *************************************************************; *** Scatter-Loading Description File generated by uVision ***; *************************************************************LR_IROM1 0x0002D000 0x00046000 { ; load region size_region ER_IROM1 0x0002D000 0x00046000 { ; load address = execution address *.o (RESET, +First) *(InRoot$$Sections) .ANY (+RO) } RW_IRAM1 0x20009340 UNINIT 0x00000100 { ; RW data *(.noinit) } RW_IRAM2 0x20009440 0x00006BC0 { ; RW data .ANY (+RW +ZI) }}
If I change my characteristic to
typedef struct{ uint8_t gps_valid; /**< GPS valid */ uint8_t num_satellites; /**< Number of GNSS satellites */ uint16_t gps_accuracy; /**< Accuracy in (m)*/ int32_t latitude; int32_t longitude; int32_t speed; uint8_t fix_ok : 1; uint8_t heading_valid : 1; uint8_t differential_soln : 1; uint8_t carrier_soln : 2; uint8_t _unused : 3; uint32_t horizontal_accuracy; uint16_t pdop;} __attribute__((packed)) ble_gps_t;
Then increasing the softdevice RAM allocation by 448 bytes (which is about as much as I can spare) still isn't enough for all my services to be initialised, I get NRF_ERROR_NO_MEM when calling sd_ble_gatts_characteristic_add.
But, if I remove the pdop field, so my characteristic is now
typedef struct{ uint8_t gps_valid; /**< GPS valid */ uint8_t num_satellites; /**< Number of GNSS satellites */ uint16_t gps_accuracy; /**< Accuracy in (m)*/ int32_t latitude; int32_t longitude; int32_t speed; uint8_t fix_ok : 1; uint8_t heading_valid : 1; uint8_t differential_soln : 1; uint8_t carrier_soln : 2; uint8_t _unused : 3; uint32_t horizontal_accuracy;} __attribute__((packed)) ble_gps_t;
Then I don't need to change my scatter file at all.
Why do those extra 2 bytes mean the softdevice requires so much more RAM?
